Kohler CV18, CV730, CV20, CV26, CV22 Service Manual

COMMAND CV17-750

VERTICAL CRANKSHAFT

SERVICE MANUAL

Contents

Section 1. Safety and General Information ............................................................................

Section 2. Tools & Aids ..........................................................................................................

Section 3. Troubleshooting .....................................................................................................

Section 4. Air Cleaner and Air Intake System ........................................................................

Section 5. Fuel System and Governor....................................................................................

Section 5B. Electronic Fuel Injection (EFI) Fuel System ......................................................

Section 6. Lubrication System ................................................................................................

1

2

3

4

5

5B

6

Section 7. Retractable Starter .................................................................................................

Section 8. Electrical System and Components .....................................................................

Section 9. Disassembly ...........................................................................................................

Section 10. Inspection and Reconditioning ...........................................................................

Section 11. Reassembly...........................................................................................................

7

8

9

10

11

Safety and General Information

Section 1

Safety and General Information

Safety Precautions

To ensure safe operation please read the following statements and understand their meaning. Also
refer to your equipment manufacturer's manual for other important safety information. This manual
contains safety precautions which are explained below. Please read carefully.

WARNING

Warning is used to indicate the presence of a hazard that can cause severe personal injury, death,
or substantial property damage if the warning is ignored.

CAUTION

Caution is used to indicate the presence of a hazard that will or can cause minor personal injury or
property damage if the caution is ignored.

Section 1

1

NOTE

Note is used to notify people of installation, operation, or maintenance information that is important
but not hazard-related.

For Y our Safety!

These precautions should be followed at all times. Failure to follow these precautions could result in injury to yourself
and others.

WARNING

Accidental Starts can cause
severe injury or death.

Disconnect and ground spark plug
leads before servicing.

Accidental Starts!

Disabling engine. Accidental starting
can cause severe injury or death.

Before working on the engine or
equipment, disable the engine as follows:

1) Disconnect the spark plug lead(s). 2)
Disconnect negative (-) battery cable
from battery.

WARNING

Rotating Parts can cause severe
injury.

Stay away while engine is in
operation.

Rotating Parts!

Keep hands, feet, hair, and clothing away
from all moving parts to prevent injury.
Never operate the engine with covers,
shrouds, or guards removed.

Hot Parts can cause severe burns.

Do not touch engine while operating
or just after stopping.

Hot Parts!

Engine components can get extremely
hot from operation. To prevent severe
burns, do not touch these areas while the
engine is running—or immediately after
it is turned off. Never operate the engine
with heat shields or guards removed.

WARNING

1.1

Section 1
Safety and General Information

WARNING

Explosive Fuel can cause fires
and severe burns.

Do not fill the fuel tank while the
engine is hot or running.

Explosive Fuel!

Gasoline is extremely flammable and its
vapors can explode if ignited. Store
gasoline only in approved containers, in
well ventilated, unoccupied buildings,
away from sparks or flames. Do not fill
the fuel tank while the engine is hot or
running, since spilled fuel could ignite if
it comes in contact with hot parts or
sparks from ignition. Do not start the
engine near spilled fuel. Never use
gasoline as a cleaning agent.

WARNING

Cleaning Solvents can cause severe
injury or death.

Use only in well ventilated areas
away from ignition sources.

Flammable Solvents!

Carburetor cleaners and solvents are
extremely flammable. Keep sparks,
flames, and other sources of ignition
away from the area. Follow the cleaner
manufacturer’s warnings and
instructions on its proper and safe use.
Never use gasoline as a cleaning agent.

WARNING WARNING

Carbon Monoxide can cause severe
nausea, fainting or death.

Avoid inhaling exhaust fumes, and
never run the engine in a closed
building or confined area.

Lethal Exhaust Gases!

Engine exhaust gases contain poisonous
carbon monoxide. Carbon monoxide is
odorless, colorless, and can cause death if
inhaled. Avoid inhaling exhaust fumes,
and never run the engine in a closed
building or confined area.

WARNING

Uncoiling Spring can cause severe
injury.

Wear safety goggles or face
protection when servicing
retractable starter.

Spring Under T ension!

Retractable starters contain a powerful,
recoil spring that is under tension.
Always wear safety goggles when
servicing retractable starters and
carefully follow instructions in
"Retractable Starter" Section 7 for
relieving spring tension.

Explosive Gas can cause fires and
severe acid burns.

Charge battery only in a well
ventilated area. Keep sources of
ignition away.

Explosive Gas!

Batteries produce explosive hydrogen gas
while being charged. To prevent a fire or
explosion, charge batteries only in well
ventilated areas. Keep sparks, open
flames, and other sources of ignition
away from the battery at all times. Keep
batteries out of the reach of children.
Remove all jewelry when servicing
batteries.

Before disconnecting the negative
(-) ground cable, make sure all switches
are OFF. If ON, a spark will occur at the
ground cable terminal which could cause
an explosion if hydrogen gas or gasoline
vapors are present.

CAUTION

Electrical Shock can cause injury.

Do not touch wires while engine is
running.

Electrical Shock!

Never touch electrical wires or
components while the engine is running.
They can be sources of electrical shock.

1.2

Engine Identification Numbers

When ordering parts, or in any communication
involving an engine, always give the Model,
Specification and Serial Numbers, including letter
suffixes if there are any.

The engine identification numbers appear on a decal,
or decals, affixed to the engine shrouding. See Figure
1-1. An explanation of these numbers is shown in
Figure 1-2.

Section 1

Safety and General Information

1

Identification
Decal

Figure 1-1. Engine Identification Decal Location.

A. Model No.

Command Engine
Vertical Crankshaf t

Horsepower

17 = 17 HP
18 = 18 HP
20 = 20 HP
22 = 22 HP
23 = 23 HP
25 = 25 HP
26 = 26 HP

B. Spec. No.

Engine Model Code
Code Model

72 CV17
61 CV18
65 CV20
67 CV22 (624 cc)
69 CV25
75 CV22/23 (674 cc)
79 CV26

C V 18 S

or

61500

Numerical Designation

730
740
745
750

or

Variation of
Basic Engine

Version Code

S = Electric Start

CV730-0001
CV740-0001
CV745-0001
CV750-0001

Complete Spec Number
(Incorporating Model No.
with V ariation No. of
Basic Spec.)

C. Serial No.

Year Manufactured Code
Code Year

21 1991
22 1992
23 1993
24 1994
25 1995
26 1996
27 1997
28 1998
29 1999

Figure 1-2. Explanation of Engine Identification Numbers.

3305810334

Factory Code

Code Year

30 2000
31 2001
32 2002
33 2003
34 2004
35 2005
36 2006
37 2007

1.3

Section 1
Safety and General Information

Oil Recommendations

Using the proper type and weight of oil in the
crankcase is extremely important. So is checking oil
daily and changing oil regularly. Failure to use the
correct oil, or using dirty oil, causes premature engine
wear and failure.

Oil T ype

Use high-quality detergent oil of API (American
Petroleum Institute) Service Class SG, SH, SJ or
higher. Select the viscosity based on the air

temperature at the time of operation as shown in the
following table.

**

*Use of synthetic oil having 5W-20 or 5W-30 rating is
acceptable, up to 40°F.
**Synthetic oils will provide better starting in extreme
cold (below -10

NOTE: Using other than service class SG, SH, SJ or

NOTE: Synthetic oils meeting the listed

A logo or symbol on oil containers identifies the API
service class and SAE viscosity grade. See Figure 1-3.

°F).

higher oil or extending oil change intervals
longer than recommended can cause engine
damage.

classifications may be used with oil changes
performed at the recommended intervals.
However, to allow piston rings to properly
seat, a new or rebuilt engine should be
operated for at least 50 hours using standard
petroleum based oil before switching to
synthetic oil.

*

Refer to Section 6 - “Lubrication System” for detailed
procedures on checking the oil, changing the oil and
changing the oil filter.

Fuel Recommendations

WARNING: Explosive Fuel!

Gasoline is extremely flammable and its vapors can explode if
ignited. Before servicing the fuel system, make sure there are no
sparks, open flames or other sources of ignition nearby as these
can ignite gasoline vapors. Disconnect and ground the spark
plug leads to prevent the possibility of sparks from the ignition
system.

General Recommendations

Purchase gasoline in small quantities and store in clean,
approved containers. A container with a capacity of 2
gallons or less with a pouring spout is recommended.
Such a container is easier to handle and helps eliminate
spillage during refueling.

Do not use gasoline left over from the previous season,
to minimize gum deposits in your fuel system and to
ensure easy starting.

Do not add oil to the gasoline.

Do not overfill the fuel tank. Leave room for the fuel to
expand.

Fuel Type

For best results, use only clean, fresh, unleaded gasoline
with a pump sticker octane rating of 87 or higher. In
countries using the Research method, it should be 90
octane minimum.

Unleaded gasoline is recommended as it leaves less
combustion chamber deposits and reduces harmful
exhaust emissions. Leaded gasoline is not
recommended and must not be used on EFI engines, or
on other models where exhaust emissions are
regulated.

Gasoline/Alcohol blends

Gasohol (up to 10% ethyl alcohol, 90% unleaded
gasoline by volume) is approved as a fuel for Kohler
engines. Other gasoline/alcohol blends are not
approved.

Figure 1-3. Oil Container Logo.

1.4

Gasoline/Ether blends

Methyl Tertiary Butyl Ether (MTBE) and unleaded
gasoline blends (up to a maximum of 15% MTBE by
volume) are approved as a fuel for Kohler engines.
Other gasoline/ether blends are not approved.

Periodic Maintenance Instructions

Section 1

Safety and General Information

WARNING: Accidental St arts!

Disabling engine. Accidental starting can cause severe injury or death. Before working on the engine or equipment,
disable the engine as follows: 1) Disconnect the spark plug lead(s). 2) Disconnect negative (-) battery cable from battery.

Maintenance Schedule

These required maintenance procedures should be performed at the frequency stated in the table. They should
also be included as part of any seasonal tune-up.

Maintenance RequiredFrequency

• Fill fuel tank. Section 5

Daily or Before

Starting Engine

Every 25 Hours

Every 100 Hours

Every 200 Hours

Every 250 Hours

Annually or

Every 500 Hours
Every 500 Hours

Every 1500 Hours

¹Perform these maintenance procedures more frequently under extremely dusty, dirty conditions.
²Only required for Denso starters. Not necessary on Delco starters. Have a Kohler Engine Service Dealer perform this service.
³Cleanout Kits 25 755 20-S (black) or 25 755 21-S (gold) allow cooling areas to be cleaned without removing shrouds.

• Check oil level. Section 6

• Check air cleaner for dirty

• Check air intake and cooling areas, clean as necessary1. Section 4

• Service precleaner element1. Section 4

• Replace air cleaner element

• Change oil. (More frequently under severe conditions.) Section 6

• Remove cooling shrouds and clean cooling areas

• Check oil cooler fins, clean as necessary (if equipped). Section 6

• Check spark plug condition and gap. Section 8

• Change oil filter. Section 6

• Check fuel filter (carbureted models) Section 5

• Replace heavy-duty air cleaner element and check inner element1. Section 4

• Have bendix starter drive serviced2. Section 8

• Have solenoid shift starter disassembled and cleaned2. Section 8

• Have crankshaft splines lubricated2. Section 2

• Replace fuel filter1 (EFI engines). Section 5B

1

, loose, or damaged parts. Section 4

1

. Section 4

1,3

. Section 4

Refer to:

1

Storage

If the engine will be out of service for two months or
more, use the following storage procedure:

1. Clean the exterior surfaces of the engine. On
Electronic Fuel Injected (EFI) engines, avoid
spraying water at the wiring harness or any of
the electrical components.

2. Change the oil and oil filter while the engine is
still warm from operation. See “Change Oil and
Oil Filter” in Section 6.

3. The fuel system must be completely emptied, or
the gasoline must be treated with a stabilizer to
prevent deterioration. If you choose to use a
stabilizer, follow the manufacturer’s
recommendations, and add the correct amount
for the capacity of the fuel system.

Fill the fuel tank with clean, fresh gasoline. Run
the engine for 2 to 3 minutes to get stabilized fuel
into the rest of the system. Close the fuel shut-off
valve when the unit is being stored or
transported.

To empty the system, run the engine until the
tank and the system is empty.

4. Remove the spark plugs and add one tablespoon
of engine oil into each spark plug hole. Install the
spark plugs, but do not connect the plug leads.
Crank the engine two or three revolutions.

5. On equipment with an EFI engine, disconnect the
battery or use a battery minder to keep the
battery charged during storage.

6. Store the engine in a clean, dry place.

1.5

Section 1
Safety and General Information

Dimensions in millimeters.
Inch equivalents shown in [ ].

Figure 1-4. Typical Engine Dimensions CV Series with Standard Flat Air Cleaner.

1.6

Section 1

Safety and General Information

Dimensions in millimeters.
Inch equivalents shown in [ ].

1

Figure 1-5. Typical Engine Dimensions CV Series with Commercial Mower Air Cleaner.

1.7

Section 1
Safety and General Information

Dimensions in millimeters.
Inch equivalents shown in [ ].

Figure 1-6. T ypical Engine Dimensions CV EFI Series with Heavy-Duty Air Cleaner.

1.8

Section 1

Safety and General Information

General Specifications

Power (@3600 RPM, exceeds Society of Automotive Engineers-Small Engine Test Code J1940.)

CV17 ...........................................................................................................................................12.7 kW (17 HP)

CV18 ...........................................................................................................................................13.4 kW (18 HP)

CV20 ...........................................................................................................................................14.9 kW (20 HP)

CV22 ...........................................................................................................................................16.4 kW (22 HP)

CV23 ...........................................................................................................................................17.2 kW (23 HP)

CV25,CV730 ..............................................................................................................................18.6 kW (25 HP)

CV26 ...........................................................................................................................................19.4 kW (26 HP)

CV740 .........................................................................................................................................20.1 kW (27 HP)

CV745 .........................................................................................................................................20.9 kW (28 HP)

CV750 .........................................................................................................................................22.4 kW (30 HP)

Peak Torque

CV17 @ 2200 RPM .................................................................................................................... 35.9 N·m (28.7 ft. lb.)

CV18 @ 2200 RPM .................................................................................................................... 42.5 N·m (31.4 ft. lb.)

CV20 @ 2400 RPM .................................................................................................................... 45.1 N·m (33.3 ft. lb.)

CV22 @ 2200 RPM .................................................................................................................... 49.6 N·m (36.6 ft. lb.)

CV23 @ 2400 RPM .................................................................................................................... 54.5 N·m (40.2 ft. lb.)

CV25,CV730 @ 2400 RPM........................................................................................................ 55.6 N·m (41.0 ft. lb.)

CV26 @ 2800 RPM .................................................................................................................... 54.2 N·m (40.0 ft. lb.)

CV740 @ 2800 RPM .................................................................................................................. 56.9 N·m (42.0 ft. lb.)

CV745 @ 2400 RPM .................................................................................................................. 60.0 N·m (44.3 ft. lb.)

CV750 @ 2600 RPM .................................................................................................................. 63.8 N·m (47.1 ft. lb.)

1

1

Bore

CV17 ...........................................................................................................................................73 mm (2.87 in.)

CV18,CV20,CV22 (624 cc) ....................................................................................................... 77 mm (3.03 in.)

CV22/23 (674 cc) ....................................................................................................................... 80 mm (3.15 in.)

CV25,CV26,CV730-750 ........................................................................................................... 83 mm (3.27 in.)

Stroke

CV17-745 ...................................................................................................................................67 mm (2.64 in.)

CV750 .........................................................................................................................................69 mm (2.7 in.)

Displacement

CV17 ...........................................................................................................................................561 cc (34 cu. in.)

CV18,CV20,CV22 (624 cc) ....................................................................................................... 624 cc (38 cu. in.)

CV22/23 (674 cc) ....................................................................................................................... 674 cc (41 cu. in.)

CV25,CV26,CV730-745 ........................................................................................................... 725 cc (44 cu. in.)

CV750 .........................................................................................................................................755 cc (46 cu. in.)

Compression Ratio

CV17 ...........................................................................................................................................8.2:1

CV18,CV20,CV22/23 ................................................................................................................8.5:1

CV25,CV26,CV730-745 ........................................................................................................... 9.0:1

CV750 .........................................................................................................................................9.4:1

Dry Weight

CV17,CV18,CV20,CV22/23 ..................................................................................................... 41 kg (90 lb.)

CV25,CV26,CV730-745 ........................................................................................................... 43 kg (94 lb.)

CV750 .........................................................................................................................................48 kg (105 lb.)

1

Values are in Metric units. Values in parentheses are English equivalents. Lubricate threads with engine oil

prior to assembly.

1.9

Section 1
Safety and General Information

General Specifications1 cont.

Oil Capacity (w/filter) - approximate,

determined by oil filter and oil cooler used:........................................................ 1.6-1.8 L (1.7-1.9 U.S. qt.)

Angle of Operation - Maximum (At Full Oil Level) All Directions .................. 25°

Blower Housing and Sheet Metal

M5 Fasteners Torque ................................................................................................ 6.2 N·m (55 in. lb.) into new holes

4.0 N·m (35 in. lb.) into used holes

M6 Fasteners Torque ................................................................................................ 10.7 N·m (95 in. lb.) into new holes

7.3 N·m (65 in. lb.) into used holes

Rectifier-Regulator Fastener Torque ..................................................................... 1.4 N·m (12.6 in. lb.)

Camshaft

End Play (With Shim) .............................................................................................. 0.076/0.127 mm (0.0030/0.0050 in.)

Running Clearance ................................................................................................... 0.025/0.063 mm (0.0010/0.0025 in.)

Bore I.D.

New ..................................................................................................................... 20.000/20.025 mm (0.7874/0.7884 in.)

Max. Wear Limit ................................................................................................ 20.038 mm (0.7889 in.)

Camshaft Bearing Surface O.D.

New ..................................................................................................................... 19.962/19.975 mm (0.7859/0.7864 in.)

Max. Wear Limit ................................................................................................ 19.959 mm (0.7858 in.)

Carburetor and Intake Manifold

Intake Manifold Mounting Fastener Torque

Torque in Two Stages ........................................................................................ first to 7.4 N·m (66 in. lb.)

finally to 9.9 N·m (88 in. lb.)

Carburetor Mounting Nut Torque ......................................................................... 6.2-7.3 N·m (55-65 in. lb.)

Connecting Rod

Cap Fastener Torque (torque in increments)

8 mm straight shank ......................................................................................... 22.7 N·m (200 in. lb.)

8 mm step-down ............................................................................................... 14.7 N·m (130 in. lb.)

6 mm straight shank ......................................................................................... 11.3 N·m (100 in. lb.)

Connecting Rod-to-Crankpin Running Clearance

New ..................................................................................................................... 0.030/0.055 mm (0.0012/0.0022 in.)

Max. Wear Limit ................................................................................................ 0.070 mm (0.0028 in.)

Connecting Rod-to-Crankpin Side Clearance ...................................................... 0.26/0.63 mm (0.0102/0.0248 in.)

Connecting Rod-to-Piston Pin Running Clearance............................................. 0.015/0.028 mm (0.0006/0.0011 in.)

Piston Pin End I.D.

New ..................................................................................................................... 17.015/17.023 mm (0.6699/0.6702 in.)

Max. Wear Limit ................................................................................................ 17.036 mm (0.6707 in.)

1

Values are in Metric units. Values in parentheses are English equivalents. Lubricate threads with engine oil

prior to assembly.

1.10

Section 1

Safety and General Information

Crankcase

Governor Cross Shaft Bore I.D.

6 mm Shaft

New ..............................................................................................................6.025/6.050 mm (0.2372/0.2382 in.)

Max. Wear Limit ........................................................................................6.063 mm (0.2387 in.)

8 mm Shaft

New ..............................................................................................................8.025/8.075 mm (0.3159/0.3179 in.)

Max. Wear Limit ........................................................................................8.088 mm (0.3184 in.)

Breather Cover Fastener Torque ........................................................................ 7.3 N·m (65 in. lb.)

Oil Drain Plug Torque .......................................................................................... 13.6 N·m (10 ft. lb.)

Oil Pan

Oil Pan Fastener Torque ...................................................................................... 24.4 N·m (216 in. lb.)

Crankshaft

End Play (Free) ......................................................................................................0.070/0.590 mm (0.0028/0.0230 in.)

Crankshaft Bore (In Crankcase)

New ................................................................................................................. 40.965/41.003 mm (1.6128/1.6143 in.)

Max. Wear Limit ............................................................................................41.016 mm (1.6148 in.)

1

Crankshaft to Sleeve Bearing (Crankcase)

Running Clearance - New ............................................................................0.03/0.09 mm (0.0012/0.0035 in.)

Crankshaft Bore (In Oil Pan) - New ...................................................................40.987/40.974 mm (1.6136/1.6131 in.)

Crankshaft Bore (In Oil Pan)-to-Crankshaft

Running Clearance - New ............................................................................0.039/0.074 mm (0.0015/0.0029 in.)

Flywheel End Main Bearing Journal

O.D. - New ......................................................................................................40.913/40.935 mm (1.6107/1.6116 in.)

O.D. - Max. Wear Limit .................................................................................40.84 mm (1.608 in.)

Max. Taper ...................................................................................................... 0.022 mm (0.0009 in.)

Max. Out-of-Round .......................................................................................0.025 mm (0.0010 in.)

Oil Pan End Main Bearing Journal

O.D. - New ......................................................................................................40.913/40.935 mm (1.6107/1.6116 in.)

O.D. - Max. Wear Limit .................................................................................40.84 mm (1.608 in.)

Max. Taper ...................................................................................................... 0.022 mm (0.0009 in.)

Max. Out-of-Round .......................................................................................0.025 mm (0.0010 in.)

Connecting Rod Journal

O.D. - New ......................................................................................................35.955/35.973 mm (1.4156/1.4163 in.)

O.D. - Max. Wear Limit .................................................................................35.94 mm (1.415 in.)

Max. Taper ...................................................................................................... 0.018 mm (0.0007 in.)

Max. Out-of-Round .......................................................................................0.025 mm (0.0010 in.)

Crankshaft T.I.R.

PTO End, Crank in Engine ............................................................................ 0.279 mm (0.0110 in.)

Entire Crank, in V-Blocks ............................................................................. 0.10 mm (0.0039 in.)

1.11

Section 1
Safety and General Information

Cylinder Bore

Cylinder Bore I.D.

New - CV17 ............................................................................................. 73.006/73.031 mm (2.8742/2.8752 in.)

New - CV18,CV20,CV22 (624 cc) ......................................................... 77.000/77.025 mm (3.0315/3.0325 in.)

New - CV22/23 (674 cc) ......................................................................... 80.000/80.025 mm (3.1496/3.1506 in.)

New - CV25,CV26,CV730-750 ............................................................. 82.988/83.013 mm (3.2672/3.2682 in.)

Max. Wear Limit - CV17........................................................................ 73.070 mm (2.8757 in.)

Max. Wear Limit - CV18,CV20,CV22 (624 cc) .................................... 77.063 mm (3.0340 in.)

Max. Wear Limit - CV22/23 (674 cc) .................................................... 80.065 mm (3.1522 in.)

Max. Wear Limit - CV25,CV26,CV730-750 ........................................ 83.051 mm (3.2697 in.)

Max. Out-of-Round CV17 ..................................................................... 0.13 mm (0.0051 in.)

Max. Out-of-Round CV18-750 ............................................................. 0.12 mm (0.0047 in.)

Max. Taper ............................................................................................... 0.05 mm (0.0020 in.)

Cylinder Head

Cylinder Head Fastener Torque

Hex Flange Nut - Torque in Two Stages .............................................. first to 16.9 N·m (150 in. lb.)

finally to 33.9 N·m (300 in. lb.)

Head Bolt - Torque in Two Stages ........................................................ first to 22.6 N·m (200 in. lb.)

finally to 41.8 N·m (370 in. lb.)

Max. Out-of-Flatness ..................................................................................... 0.076 mm (0.003 in.)

Rocker Arm Screw Torque ........................................................................... 11.3 N·m (100 in. lb.)

Fan/Flywheel

Fan Fastener Torque ...................................................................................... 9.9 N·m (88 in. lb.)

Flywheel Retaining Screw Torque .............................................................. 66.4 N·m (49 ft. lb.)

Governor

Governor Cross Shaft-to-Crankcase Running Clearance

6 mm Shaft .............................................................................................. 0.013/0.075 mm (0.0005/0.0030 in.)

8 mm Shaft .............................................................................................. 0.025/0.126 mm (0.0009/0.0049 in.)

Governor Cross Shaft O.D.

6 mm Shaft

New ....................................................................................................... 5.975/6.012 mm (0.2352/0.2367 in.)

Max. Wear Limit .................................................................................. 5.962 mm (0.2347 in.)

8 mm Shaft

New ....................................................................................................... 7.949/8.000 mm (0.3129/0.3149 in.)

Max. Wear Limit .................................................................................. 7.936 mm (0.3124 in.)

Governor Gear Shaft-to-Governor

Gear Running Clearance ....................................................................... 0.015/0.140 mm (0.0006/0.0055 in.)

Governor Gear Shaft O.D.

New .......................................................................................................... 5.990/6.000 mm (0.2358/0.2362 in.)

Max. Wear Limit ..................................................................................... 5.977 mm (0.2353 in.)

Governor Lever Nut Torque ........................................................................ 6.8 N·m (60 in. lb.)

1.12

Section 1

Safety and General Information

Ignition

Spark Plug Type (Champion® or Equivalent) .............................................RC12YC, XC12YC, or Platinum 3071

Spark Plug Gap ............................................................................................... 0.76 mm (0.030 in.)

Spark Plug Torque .......................................................................................... 24.4-29.8 N·m (18-22 ft. lb.)

Ignition Module Air Gap ...............................................................................0.28/0.33 mm (0.011/0.013 in.)

Ignition Module Fastener Torque ................................................................. 4.0-6.2 N·m (35-55 in. lb.)

Speed Sensor Air Gap (EFI engines) ............................................................. 1.50 ± 0.25 mm (0.059 ± 0.010 in.)

Muffler

Muffler Retaining Nuts Torque .................................................................... 24.4 N·m (216 in. lb.)

Oil Filter

Oil Filter Torque .............................................................................................. 3/4 - 1 turn after gasket contact

Oil Cooler

Oil Cooler/Adapter Nipple Torque .............................................................. 27 N·m (20 ft. lb.)

1

Piston, Piston Rings, and Piston Pin

Piston-to-Piston Pin Running Clearance ....................................................0.006/0.017 mm (0.0002/0.0007 in.)

Piston Pin Bore I.D.

New ........................................................................................................... 17.006/17.012 mm (0.6695/0.6698 in.)

Max. Wear Limit ......................................................................................17.025 mm (0.6703 in.)

Piston Pin O.D.

New ........................................................................................................... 16.995/17.000 mm (0.6691/0.6693 in.)

Max. Wear Limit ......................................................................................16.994 mm (0.6691 in.)

Top Compression Ring-to-Groove Side Clearance

CV17 ..........................................................................................................0.040/0.085 mm (0.0016/0.0033 in.)

CV18,CV20,CV22 (624 cc) ...................................................................... 0.040/0.080 mm (0.0016/0.0031 in.)

CV22/23 (674 cc) ...................................................................................... 0.030/0.076 mm (0.0012/0.0030 in.)

CV25,CV26,CV730-750 .......................................................................... 0.025/0.048 mm (0.0010/0.0019 in.)

Middle Compression Ring-to-Groove Side Clearance

CV17 ..........................................................................................................0.030/0.080 mm (0.0012/0.0031 in.)

CV18,CV20,CV22 (624 cc) ...................................................................... 0.040/0.080 mm (0.0016/0.0031 in.)

CV22/23 (674 cc) ...................................................................................... 0.030/0.076 mm (0.0012/0.0030 in.)

CV25,CV26,CV730-750 .......................................................................... 0.015/0.037 mm (0.0006/0.0015 in.)

Oil Control Ring-to-Groove Side Clearance

CV17 ..........................................................................................................0.046/0.201 mm (0.0018/0.0079 in.)

CV18,CV20,CV22 (624 cc) ...................................................................... 0.060/0.202 mm (0.0024/0.0080 in.)

CV22/23 (674 cc) ...................................................................................... 0.046/0.196 mm (0.0018/0.0077 in.)

CV25,CV26,CV730-750 .......................................................................... 0.026/0.176 mm (0.0010/0.0070 in.)

1.13

Section 1
Safety and General Information

Piston, Piston Rings, and Piston Pin cont.

Top and Middle Compression Ring End Gap

New Bore - CV17

Top Ring ............................................................................................... 0.180/0.380 mm (0.0071/0.0150 in.)

Middle Ring ......................................................................................... 0.180/0.440 mm (0.0071/0.0173 in.)

New Bore - CV18,CV20,CV22 (624 cc) ................................................. 0.25/0.45 mm (0.0098/0.0177 in.)

New Bore - CV22 (674 cc) .......................................................................0.18/0.46 mm (0.0071/0.0181 in.)

New Bore - CV25,CV26,CV730-750 ..................................................... 0.25/0.56 mm (0.0100/0.0224 in.)

Used Bore (Max.) - CV17

Top Ring ............................................................................................... 0.70 mm (0.028 in.)

Middle Ring ......................................................................................... 0.90 mm (0.035 in.)

Used Bore (Max.) - CV18,CV20,CV22 (624 cc) ..................................... 0.77 mm (0.030 in.)

Used Bore (Max.) - CV22/23 (674 cc) ..................................................... 0.80 mm (0.0315 in.)

Used Bore (Max.) - CV25,CV26,CV730-750 ......................................... 0.94 mm (0.037 in.)

Piston Thrust Face O.D.²

New - CV17 ..............................................................................................72.966/72.984 mm (2.8727/2.8734 in.)

New - CV18,CV20,CV22 (624 cc) .......................................................... 76.967/76.985 mm (3.0302/3.0309 in.)

New - CV22/23 (674 cc) .......................................................................... 79.963/79.979 mm (3.1481/3.1488 in.)

New - CV25,CV26,CV730-750 .............................................................. 82.986 mm (3.2671 in.)

Max. Wear Limit - CV17......................................................................... 72.839 mm (2.8677 in.)

Max. Wear Limit - CV18,CV20,CV22 (624 cc) .....................................76.840 mm (3.0252 in.)

Max. Wear Limit - CV22 (674 cc) ........................................................... 79.831 mm (3.1430 in.)

Max. Wear Limit - CV25,CV26,CV730-750 .........................................82.841 mm (3.2614 in.)

Piston Thrust Face-to-Cylinder Bore² Running Clearance

New - CV17 ..............................................................................................0.022/0.065 mm (0.0009/0.0026 in.)

New - CV18,CV20,CV22 (624 cc) .......................................................... 0.014/0.057 mm (0.0005/0.0022 in.)

New - CV22/23 (674 cc) .......................................................................... 0.021/0.062 mm (0.0008/0.0024 in.)

New - CV25,CV26,CV730-750 .............................................................. 0.001/0.045 mm (0.039/0.0018 in.)

Speed Control Bracket

Fastener Torque............................................................................................... 10.7 N·m (95 in. lb.) into new holes

7.3 N·m (65 in. lb.) into used holes

Starter Assembly

Thru Bolt Torque

UTE/Johnson Electric, Eaton (Inertia Drive)......................................... 4.5-5.7 N·m (40-50 in. lb.)

Nippondenso (Solenoid Shift)................................................................ 4.5-7.5 N·m (40-84 in. lb.)

Delco-Remy (Solenoid Shift) .................................................................. 5.6-9.0 N·m (49-79 in. lb.)

Mounting Screw Torque (All) ....................................................................... 15.3 N·m (135 in. lb.)

Brush Holder Mounting Screw Torque

Delco-Remy Starter ................................................................................. 2.5-3.3 N·m (22-29 in. lb.)

Solenoid (Starter)

Mounting Hardware Torque

Nippondenso Starter .............................................................................. 6.0-9.0 N·m (53-79 in. lb.)

Delco-Remy Starter ................................................................................. 4.0-6.0 N·m (35-53 in. lb.)

Nut, Positive (+) Brush Lead Torque

Nippondenso Starter .............................................................................. 8.0-12.0 N·m (71-106 in. lb.)

Delco-Remy Starter ................................................................................. 8.0-11.0 N·m (71-97 in. lb.)

²Measure 6 mm (0.236 in.) above the bottom of the piston skirt at right angles to the piston pin.

1.14

Section 1

Safety and General Information

Stator

Mounting Screw Torque ................................................................................ 6.2 N·m (55 in. lb.)

Valve Cover

Valve Cover Fastener Torque

Gasket Style Cover ..................................................................................3.4 N·m (30 in. lb.)

Black O-Ring Style Cover

w/Shoulder Screws ............................................................................5.6 N·m (50 in. lb.)

w/Flange Screws and Spacers ..........................................................9.9 N·m (88 in. lb.)

Yellow or Brown O-Ring Style Cover w/Integral Metal Spacers..... 6.2 N·m (55 in. lb.)

Valves and Valve Lifters

Hydraulic Valve Lifter to Crankcase Running Clearance ........................ 0.0241/0.0501 mm (0.0009/0.0020 in.)

Intake Valve Stem-to-Valve Guide Running Clearance ........................... 0.038/0.076 mm (0.0015/0.0030 in.)

Exhaust Valve Stem-to-Valve Guide Running Clearance ........................ 0.050/0.088 mm (0.0020/0.0035 in.)

Intake Valve Guide I.D.

New ........................................................................................................... 7.038/7.058 mm (0.2771/0.2779 in.)

Max. Wear Limit ......................................................................................7.134 mm (0.2809 in.)

1

Exhaust Valve Guide I.D.

New ........................................................................................................... 7.038/7.058 mm (0.2771/0.2779 in.)

Max. Wear Limit ......................................................................................7.159 mm (0.2819 in.)

Valve Guide Reamer Size

Standard ...................................................................................................7.048 mm (0.2775 in.)

0.25 mm O.S. .............................................................................................7.298 mm (0.2873 in.)

Intake Valve Minimum Lift ...........................................................................8.07 mm (0.3177 in.)

Exhaust Valve Minimum Lift ....................................................................... 8.07 mm (0.3177 in.)

Nominal Valve Seat Angle ............................................................................ 45°

1.15

Section 1
Safety and General Information

General Torque Values

Metric Fastener T orque Recommendations for St andard Applications

Tightening Torque: N·m (in. lb.) + or - 10%

Property Class

4.8

Size
M4 1.2 (11) 1.7 (15) 2.9 (26) 4.1 (36) 5.0 (44) 2.0 (18)
M5 2.5 (22) 3.2 (28) 5.8 (51) 8.1 (72) 9.7 (86) 4.0 (35)
M6 4.3 (38) 5.7 (50) 9.9 (88) 14.0 (124) 16.5 (146) 6.8 (60)
M8 10.5 (93) 13.6 (120) 24.4 (216) 33.9 (300) 40.7 (360) 17.0 (150)

5.8

8.8 10.9 12.9

Noncritical

Fasteners

Into Aluminum

Tightening Torque: N·m (ft. lb.) + or - 10%

Property Class

4.8

M10 21.7 (16) 27.1 (20) 47.5 (35) 66.4 (49) 81.4 (60) 33.9 (25)
M12 36.6 (27) 47.5 (35) 82.7 (61) 116.6 (86) 139.7 (103) 61.0 (45)
M14 58.3 (43) 76.4 (55) 131.5 (97) 184.4 (136) 219.7 (162) 94.9 (70)

5.8

8.8

10.9

12.9

Noncritical

Fasteners

Into Aluminum

1.16

Safety and General Information

English Fastener T orque Recommendations for St andard Applications

Section 1

Tightening Torque: N·m (in. lb.) + or - 20%

Bolts, Screws, Nuts and Fasteners
Assembled Into Cast Iron or Steel

Grade 2 Grade 5 Grade 8

Size
8-32 2.3 (20) 2.8 (25) --------- 2.3 (20)
10-24 3.6 (32) 4.5 (40) --------- 3.6 (32)
10-32 3.6 (32) 4.5 (40) --------- ---------
1/4-20 7.9 (70) 13.0 (115) 18.7 (165) 7.9 (70)
1/4-28 9.6 (85) 15.8 (140) 22.6 (200) ---------
5/16-18 17.0 (150) 28.3 (250) 39.6 (350) 17.0 (150)
5/16-24 18.7 (165) 30.5 (270) --------- ---------
3/8-16 29.4 (260) --------- --------- ---------
3/8-24 33.9 (300) --------- --------- ---------

Grade 2 or 5
Fasteners Into
Aluminum

Tightening Torque: N·m (ft. lb.) + or - 20%

Size
5/16-24 --------- ---------- 40.7 (30) --------­3/8-16 --------- 47.5 (35) 67.8 (50) --------­3/8-24 --------- 54.2 (40) 81.4 (60) --------­7/16-14 47.5 (35) 74.6 (55) 108.5 (80) --------­7/16-20 61.0 (45) 101.7 (75) 142.4 (105) --------­1/2-13 67.8 (50) 108.5 (80) 155.9 (115) --------­1/2-20 94.9 (70) 142.4 (105) 223.7 (165) --------­9/16-12 101.7 (75) 169.5 (125) 237.3 (175) --------­9/16-18 135.6 (100) 223.7 (165) 311.9 (230) --------­5/8-11 149.2 (110) 244.1 (180) 352.6 (260) --------­5/8-18 189.8 (140) 311.9 (230) 447.5 (330) --------­3/4-10 199.3 (150) 332.2 (245) 474.6 (350) --------­3/4-16 271.2 (200) 440.7 (325) 637.3 (470) ---------

1

Torque

Conversions

N·m = in. lb. x 0.113
N·m = ft. lb. x 1.356
in. lb. = N·m x 8.85
ft. lb. = N·m x 0.737

1.17

Section 2

Section 2

Tools & Aids

Tools & Aids

Certain quality tools are designed to help you perform specific disassembly, repair, and reassembly procedures.
By using tools designed for the job, you can properly service engines easier, faster, and safer! In addition, you’ll
increase your service capabilities and customer satisfaction by decreasing engine downtime.

Here is the list of tools and their source.

Separate Tool Suppliers:

Kohler Tools
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2.1

Section 2
Tools & Aids

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Section 2

Tools & Aids

2

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2.3

Section 2
Tools & Aids

Special Tools You Can Make

Flywheel Holding Tool

A flywheel holding tool can be made out of an old
junk flywheel ring gear as shown in Figure 2-1, and
used in place of a strap wrench.

1. Using an abrasive cut-off wheel, cut out a six
tooth segment of the ring gear as shown.

2. Grind off any burrs or sharp edges.

3. Invert the segment and place it between the
ignition bosses on the crankcase so that the tool
teeth engage the flywheel ring gear teeth. The
bosses will lock the tool and flywheel in
position for loosening, tightening or removing
with a puller.

2. Remove the studs of a Posi-Lock rod or grind off
the aligning steps of a Command rod, so the joint
surface is flat.

3. Find a 1 in. long capscrew with the correct
thread size to match the threads in the
connecting rod.

4. Use a flat washer with the correct I.D. to slip on
the capscrew and approximately 1” O.D. (Kohler
Part No. 12 468 05-S). Assemble the capscrew
and washer to the joint surface of the rod, as
shown in Figure 2-2.

Figure 2-1. Flywheel Holding Tool.

Rocker Arm/Crankshaft Tool

A spanner wrench to lift the rocker arms or turn the
crankshaft may be made out of an old junk connecting
rod.

1. Find a used connecting rod from a 10 HP or
larger engine. Remove and discard the rod cap.

Figure 2-2. Rocker Arm/Crankshaf t T ool.

2.4

Section 3

Troubleshooting

Troubleshooting Guide

When troubles occur, be sure to check the simple
causes which, at first, may seem too obvious to be
considered. For example, a starting problem could be
caused by an empty fuel tank.

Some general common causes of engine troubles are
listed below. Use these to locate the causing factors.
Refer to the specific section(s) within this service
manual for more detailed information.

Engine Cranks But Will Not Start

1. Empty fuel tank.

2. Fuel shut-off valve closed.

3. Poor fuel, dirt or water in the fuel system.

4. Clogged fuel line.

5. Spark plug lead(s) disconnected.

6. Key switch or kill switch in “off” position.

7. Faulty spark plugs.

8. Faulty ignition module(s).

9. SMART-SPARK
models).

10. Carburetor solenoid malfunction.

11. Diode in wiring harness failed in open circuit
mode.

12. Vacuum fuel pump malfunction, or oil in vacuum
hose.

13. Vacuum hose to fuel pump leaking/cracked.

14. Battery connected backwards.

15. Safety interlock system engaged.

Engine Starts But Does Not Keep Running

1. Restricted fuel tank cap vent.

2. Poor fuel, dirt or water in the fuel system.

3. Faulty or misadjusted choke or throttle controls.

4. Loose wires or connections that short the kill
terminal of ignition module to ground.

5. Faulty cylinder head gasket.

6. Faulty carburetor.

7. Vacuum fuel pump malfunction, or oil in vacuum
hose.

8. Leaking/cracked vacuum hose to fuel pump.

9. Intake system leak.

malfunction (applicable

™

Section 3

Troubleshooting

10. Diode in wiring harness failed in open circuit
mode.

Engine Starts Hard

1. PTO drive is engaged.

2. Dirt or water in the fuel system.

3. Clogged fuel line.

4. Loose or faulty wires or connections.

5. Faulty or misadjusted choke or throttle controls.

6. Faulty spark plugs.

7. Low compression.

8. Faulty ACR mechanism (equipped models).

9. Weak spark.

10. Fuel pump malfunction causing lack of fuel.

11. Engine overheated-cooling/air circulation
restricted.

12. Quality of fuel.

13. Flywheel key sheared.

14. Intake system leak.

Engine Will Not Crank

1. PTO drive is engaged.

2. Battery is discharged.

3. Safety interlock switch is engaged.

4. Loose or faulty wires or connections.

5. Faulty key switch or ignition switch.

6. Faulty electric starter or solenoid.

7. Seized internal engine components.

Engine Runs But Misses

1. Dirt or water in the fuel system.

2. Spark plug lead disconnected.

3. Poor quality of fuel.

4. Faulty spark plug(s).

5. Loose wires or connections that intermittently
ground the ignition kill circuit.

6. Engine overheated.

7. Faulty ignition module or incorrect air gap.

8. Carburetor adjusted incorrectly.

9. SMART-SPARK
models).

malfunction (applicable

™

3

3.1

Section 3
Troubleshooting

Engine Will Not Idle

1. Dirt or water in the fuel system.

2. Stale fuel and/or gum in carburetor.

3. Faulty spark plugs.

4. Fuel supply inadequate.

5. Idle fuel adjusting needle improperly set (some
models).

6. Idle speed adjusting screw improperly set.

7. Low compression.

8. Restricted fuel tank cap vent.

9. Engine overheated-cooling system/air circulation
problem.

Engine Overheats

1. Air intake/grass screen, cooling fins, or cooling
shrouds clogged.

2. Excessive engine load.

3. Low crankcase oil level.

4. High crankcase oil level.

5. Faulty carburetor.

6. Lean fuel mixture.

7. SMART-SPARK
models).

Engine Knocks

1. Excessive engine load.

2. Low crankcase oil level.

3. Old or improper fuel.

4. Internal wear or damage.

5. Hydraulic lifter malfunction.

6. Quality of fuel.

7. Incorrect grade of oil.

Engine Loses Power

1. Low crankcase oil level.

2. High crankcase oil level.

3. Dirty air cleaner element.

4. Dirt or water in the fuel system.

5. Excessive engine load.

6. Engine overheated.

7. Faulty spark plugs.

8. Low compression.

9. Exhaust restriction.

10. SMART-SPARK™ malfunction (applicable
models).

11. Low battery.

12. Incorrect governor setting.

malfunction (applicable

™

Engine Uses Excessive Amount of Oil

1. Incorrect oil viscosity/type.

2. Clogged or improperly assembled breather.

3. Breather reed broken.

4. Worn or broken piston rings.

5. Worn cylinder bore.

6. Worn valve stems/valve guides.

7. Crankcase overfilled.

8. Blown head gasket/overheated.

Oil Leaks from Oil Seals, Gaskets

1. Crankcase breather is clogged or inoperative.

2. Breather reed broken.

3. Loose or improperly torqued fasteners.

4. Piston blowby, or leaky valves.

5. Restricted exhaust.

External Engine Inspection

Before cleaning or disassembling the engine, make a
thorough inspection of its external appearance and
condition. This inspection can give clues to what
might be found inside the engine (and the cause)
when it is disassembled.

• Check for buildup of dirt and debris on the
crankcase, cooling fins, grass screen, and other
external surfaces. Dirt or debris on these areas are
causes of higher operating temperatures and
overheating.

• Check for obvious fuel and oil leaks, and
damaged components. Excessive oil leakage can
indicate a clogged or improperly-assembled
breather, worn/damaged seals and gaskets, or
loose or improperly-torqued fasteners.

• Check the air cleaner cover and base for damage
or indications of improper fit and seal.

• Check the air cleaner element. Look for holes,
tears, cracked or damaged sealing surfaces, or
other damage that could allow unfiltered air into
the engine. Also note if the element is dirty or
clogged. These could indicate that the engine has
been under serviced.

• Check the carburetor throat for dirt. Dirt in the
throat is further indication that the air cleaner is
not functioning properly.

3.2

• Check the oil level. Note if the oil level is within
the operating range on the dipstick, or if it is low
or overfilled.

Section 3

Troubleshooting

• Check the condition of the oil. Drain the oil into a
container - the oil should flow freely. Check for
metal chips and other foreign particles.

Sludge is a natural by-product of combustion; a
small accumulation is normal. Excessive sludge
formation could indicate overrich carburetion,
weak ignition, overextended oil change intervals
or wrong weight or type of oil was used, to name
a few.

NOTE: It is good practice to drain oil at a

location away from the workbench. Be
sure to allow ample time for complete
drainage.

Cleaning the Engine

After inspecting the external condition of the engine,
clean the engine thoroughly before disassembling it.
Also clean individual components as the engine is
disassembled. Only clean parts can be accurately
inspected and gauged for wear or damage. There are
many commercially available cleaners that will
quickly remove grease, oil, and grime from engine
parts. When such a cleaner is used, follow the

manufacturer’s instructions and safety precautions
carefully.

To test the crankcase vacuum with the manometer:

1. Insert the stopper/hose into the oil fill hole. Leave
the other tube of manometer open to atmosphere.
Make sure the shut off clamp is closed.

2. Start the engine and run at no-load high speed
(3200 to 3750 RPM).

3. Open the clamp and note the water level in the
tube.

The level in the engine side should be a
minimum of 10.2 cm (4 in.) above the level in the
open side.

If the level in the engine side is less than
specified (low/no vacuum), or the level in the
engine side is lower than the level in the open
side (pressure), check for the conditions in the
table below.

4. Close the shut off clamp before stopping the
engine.

To test the crankcase vacuum with the Vacuum/
Pressure Gauge Kit:

3

Make sure all traces of the cleaner are removed before
the engine is reassembled and placed into operation.
Even small amounts of these cleaners can quickly
break down the lubricating properties of engine oil.

Basic Engine Tests

Crankcase Vacuum Test

A partial vacuum should be present in the crankcase
when the engine is operating. Pressure in the
crankcase (normally caused by a clogged or
improperly assembled breather) can cause oil to be
forced out at oil seals, gaskets, or other available spots.

Crankcase vacuum is best measured with either a
water manometer, or a vacuum gauge (see Section 2).
Complete instructions are provided in the kits.

1. Remove the dipstick or oil fill plug/cap.

2. Install the adapter into the oil fill/dipstick tube
opening.

3. Push the barbed fitting on the gauge solidly into
the hole in the adapter.

4. Start the engine and bring it up to operating
speed (3200-3600 RPM).

5. Check the reading on the gauge. If the reading is
to the left of “0” on the gauge, vacuum or
negative pressure is indicated. If the reading is to
the right of “0” on the gauge, positive pressure is
present.

Crankcase vacuum should be 4-10 (inches of
water). If the reading is below specification, or if
pressure is present, check the following table for
possible causes and remedies.

3.3

Section 3
Troubleshooting

Possible Cause Solution

No Crankcase Vacuum/Pressure in Crankcase

1. Crankcase breather clogged or inoperative.

2. Seals and/or gaskets leaking. Loose or
improperly torqued fasteners.

3. Piston blowby or leaky valves (confirm by
inspecting components).

4. Restricted exhaust.

Compression T est

Some of these engines are equipped with an automatic
compression release (ACR) mechanism. Because of the
ACR mechanism, it is difficult to obtain an accurate
compression reading. As an alternative, perform a
cylinder leakdown test.

Cylinder Leakdown T est

A cylinder leakdown test can be a valuable alternative
to a compression test. By pressurizing the combustion
chamber from an external air source you can
determine if the valves or rings are leaking, and how
badly.

Cylinder Leakdown Tester (see Section 2) is a
relatively simple, inexpensive leakdown tester for
small engines. The tester includes a quick disconnect
for attaching the adapter hose, and a holding tool.

Leakdown T est Instructions

1. Run the engine for 3-5 minutes to warm it up.

2. Remove the spark plug(s) and the air filter from
engine.

3. Rotate the crankshaft until the piston (of cylinder
being tested) is at top dead center of the
compression stroke. Hold the engine in this
position while testing. The holding tool supplied
with the tester can be used if the PTO end of the
crankshaft is accessible. Lock the holding tool
onto the crankshaft. Install a 3/8" breaker bar into
the hole/slot of the holding tool, so it is
perpendicular to both the holding tool and
crankshaft PTO.

1. Disassemble breather, clean parts thoroughly,
reassemble, and recheck pressure.

2. Replace all worn or damaged seals and gaskets.
Make sure all fasteners are tightened securely.
Use appropriate torque values and sequences
when necessary.

3. Recondition piston, rings, cylinder bore, valves,
and valve guides.

4. Repair/replace restricted muffler/exhaust
system.

If the flywheel end is more accessible, use a
breaker bar and socket on the flywheel nut/
screw to hold it in position. An assistant may be
needed to hold the breaker bar during testing. If
the engine is mounted in a piece of equipment, it
may be possible to hold it by clamping or
wedging a driven component. Just be certain that
the engine cannot rotate off of TDC in either
direction.

4. Install the adapter into the spark plug hole, but
do not attach it to the tester at this time.

5. Connect an air source of at least 50 psi to the
tester.

6. Turn the regulator knob in the increase
(clockwise) direction until the gauge needle is in
the yellow “set” area at the low end of the scale.

7. Connect the tester quick-disconnect to the
adapter hose while firmly holding the engine at
TDC. Note the gauge reading and listen for
escaping air at the carburetor intake, exhaust
outlet, and crankcase breather.

8. Check the test results against the following table:

3.4

Section 3

Troubleshooting

Leakdown Test Results

Air escaping from crankcase breather ......................................................Rings or cylinder worn.

Air escaping from exhaust system ............................................................Defective exhaust valve/improper seating.

Air escaping from carburetor..................................................................... Defective intake valve/improper seating.

Gauge reading in “low” (green) zone........................................................ Piston rings and cylinder in good condition.

Gauge reading in “moderate” (yellow) zone............................................ Engine is still usable, but there is some

wear present. Customer should start
planning for overhaul or replacement.

Gauge reading in “high” (red) zone ..........................................................Rings and/or cylinder have considerable

wear. Engine should be reconditioned or
replaced.

3

3.5

Air Cleaner and Air Intake System

Section 4

Air Cleaner and Air Intake System

Section 4

Air Cleaners

General

These engines are equipped with a replaceable, high­density paper air cleaner element. Most are also
equipped with an oiled-foam precleaner which
surrounds the paper element.

Three different types are used. The “standard” type air
cleaner is shown in Figure 4-1. The “commercial
mower” type is shown in Figure 4-2, and the “heavy­duty” air cleaner is shown in Figure 4-9.

Service

Check the air cleaner daily or before starting the
engine. Check for and correct any buildup of dirt and

debris, along with loose or damaged components.

NOTE: Operating the engine with loose or damaged

air cleaner components could allow
unfiltered air into the engine causing
premature wear and failure.

Precleaner Service (Standard and Commercial
Mower Types)

If so equipped, wash and reoil the precleaner every 25
hours of operation (more often under extremely dusty

or dirty conditions).

To service the precleaner, see Figures 4-3 or 4-4 and
perform the following steps:

1. Loosen the cover retaining knob or unhook the
latches and remove the cover.

2. Remove the foam precleaner from the paper air
cleaner element.

4

Figure 4-1. Standard Air Cleaner.

Figure 4-2. Commercial Mower Air Cleaner .

3. Wash the precleaner in warm water with
detergent. Rinse the precleaner thoroughly until
all traces of detergent are eliminated. Squeeze out
excess water (do not wring). Allow the precleaner
to air dry.

4. Saturate the precleaner with new engine oil.
Squeeze out all excess oil.

5. Reinstall the precleaner over the paper air cleaner
element.

6. Reinstall the air cleaner cover. Secure the cover

with the two latches or the retaining knob.

4.1

Section 4
Air Cleaner and Air Intake System

Precleaner

Paper Element Service (Standard and Commercial
Mower Types)

Every 100 hours of operation (more often under
extremely dusty or dirty conditions), replace the paper
element. See Figures 4-5 or 4-6, and follow these steps:

1. Unhook the latches or loosen the cover retaining
knob and remove the cover.

2. Remove the wing nut, element cover, and air
cleaner element.

Element

Figure 4-3. Precleaner on Standard Air Cleaner .

Precleaner

Element

Figure 4-4. Precleaner on Commercial Mower T yp e
Air Cleaner.

3. Remove the precleaner (if so equipped) from the
paper element. Service the precleaner as
described in “Precleaner Service”.

4. Do not wash the paper element or use
pressurized air, as this will damage the element.
Replace a dirty, bent, or damaged element with a
genuine Kohler element. Handle new elements
carefully; do not use if the sealing surfaces are
bent or damaged.

5. Check the rubber sleeve seal for any damage or
deterioration. Replace as necessary.

6. Reinstall the paper element, precleaner, element
cover, and wing nut.

7. Reinstall the air cleaner cover and secure with the
two latches or the retaining knob.

4.2

Precleaner

Rubber Seal

Section 4

Air Cleaner and Air Intake System

Air Cleaner Base

Spitback Cup

Spitback
Cup Gasket

Air Cleaner Cover

Knob Seal

Element
Cover Nut

Knob

Figure 4-5. Air Cleaner System Components - S tandard.

*Plenum air cleaner system does not use a precleaner.

Wing Nut

Air Cleaner
Cover
(Plenum*)

Element Cover

Element

4

Element

Element Cover Nut

Element Cover

Rubber
Seal

Cover
Retaining
Knob

Figure 4-6. Air Cleaner System Components - Commercial Mower Type.

Air Cleaner
Cover (Std.)

Stud

Precleaner

Air
Cleaner
Base

4.3

Section 4
Air Cleaner and Air Intake System

Air Cleaner Components

Whenever the air cleaner cover is removed, or the
paper element or precleaner are serviced, check the
following:

Air Cleaner Element Cover and Seal - Make sure
element cover is not bent or damaged. Make sure the
rubber sleeve seal is in place on the stud to prevent
dust or dirt entry through the stud hole.

Air Cleaner Base - Make sure the base is secured
tightly to the carburetor and not cracked or damaged.

Breather Tube - Make sure the tube is attached to both
the air cleaner base and the oil separator.

NOTE: Damaged, worn or loose air cleaner

components can allow unfiltered air into the
engine causing premature wear and failure.
Tighten or replace all loose or damaged
components.

Mounting
Nuts (2)

Breather Hose

Baffle

4. Remove the base and gasket. Carefully feed the
breather hose through the base.

5. Reverse procedure to reassemble components.
Torque the two hex flange nuts to 6.2-7.3 N·m
(55-65 in. lb.) and the two lower M5 mounting
screws (where applicable) to 4.0 N·m (35 in. lb.).

Figure 4-8. Removing Base on Commercial Mower
T ype Air Cleaner.

Disassembly/Reassembly - Commercial Mower T yp e

If the base has to be separated from the carburetor
proceed as follows:

Lower Base

Seal

Base

Figure 4-7. Base Plate Removal on Standard Type.

Disassembly/Reassembly - Standard Type

If the base plate on the standard type has to be
removed, proceed as follows:

1. Remove the air cleaner components from the base
(see Figure 4-5).

2. Remove the two hex flange nuts securing the
bracket, or spitback cup with seal and baffle (if
equipped) to base. If a plastic intake manifold is
used, remove the two lower base mounting
screws. See Figure 4-7.

3. Pinch the sealing collar on the breather hose and
push it down through the hole in the base.

Mounting Screws

1. Remove the air cleaner components from the air
cleaner base (see Figure 4-6).

2. Remove the two nuts holding the air cleaner base
to the carburetor (see Figure 4-8).

3. Remove the tube from the base.

4. Separate the base from the carburetor.

5. Reverse procedure to reassemble components.
Torque air cleaner base mounting nuts to

6.2-7.3 N·m (55-65 in. lb.).

4.4

Heavy-Duty Air Cleaner

General

The heavy-duty air cleaner consists of a cylindrical
housing, typically mounted to a bracket, and
connected with a formed rubber hose to an adapter on
the carburetor or throttle body/intake manifold (EFI
units). The air cleaner housing contains a paper
element and inner element, designed for longer
service intervals. The system is CARB/EPA certified
and the components should not be altered or modified
in any way.

Section 4

Air Cleaner and Air Intake System

Inner Element

Element

Figure 4-9. Heavy-Duty Air Cleaner.

T o Service

Every 250 hours of operation (more often under
extremely dusty or dirty conditions), replace the
paper element and check the inner element. Follow
these steps.

1. Unhook the two retaining clips and remove the
end cap from the air cleaner housing.

Figure 4-10. Removing Elements.

4

3. After the element is removed, check the condition
of the inner element. It should be replaced
whenever it appears dirty, typically every other
time the main element is replaced. Clean the area
around the base of the inner element before
removing it, so dirt does not get into the engine.

4. Do not wash the paper element and inner
element or use compressed air, this will damage
the elements. Replace dirty, bent or damaged
elements with new genuine Kohler elements as
required. Handle the new elements carefully; do
not use if the sealing surfaces are bent or
damaged.

5. Check all parts for wear, cracks, or damage.
Replace any damaged components.

6. Install the new inner element, followed by the
outer element. Slide each fully into place in the
air cleaner housing.

2. Pull the air cleaner element out of the housing.
See Figure 4-10.

7. Reinstall the end cap so the dust ejector valve is
down, and secure with the two retaining clips.
See Figure 4-9.

4.5

Section 4
Air Cleaner and Air Intake System

Air Intake/Cooling System

To ensure proper cooling, make sure the grass screen,
cooling fan fins, and other external surfaces of the
engine are kept clean at all times.

Every 100 hours of operation (more often under
extremely dusty or dirty conditions), remove the
blower housing and other cooling shrouds.* Clean the
cooling fins and external surfaces as necessary. Make
sure the cooling shrouds are reinstalled.

*Cleanout kits, Kohler Part No. 25 755 20-S (black) or

25 755 21-S (gold), are recommended to aid
inspection and cleanout of the cooling fins. See
Figure 4-11.

NOTE: Operating the engine with a blocked grass

screen, dirty or plugged cooling fins, and/or
cooling shrouds removed, will cause engine
damage due to overheating.

Figure 4-11. Cleanout Kit Installed on Blower
Housing.

4.6

Fuel System and Governor

Section 5

Fuel System and Governor

Section 5

Description

The Command vertical twins use two different types
of fuel systems; carbureted, or electronic fuel injection
(EFI).

This section covers the standard carbureted fuel
systems. The EFI fuel systems are covered in
subsection 5B. The governor systems used are covered
at the end of this section.

WARNING: Explosive Fuel!

Gasoline is extremely flammable and its vapors can explode
if ignited. Store gasoline only in approved containers, in
well ventilated, unoccupied buildings, away from sparks or
flames. Do not fill the fuel tank while the engine is hot or
running, since spilled fuel could ignite if it comes in contact
with hot parts or sparks from ignition. Do not start the
engine near spilled fuel. Never use gasoline as a cleaning
agent.

Fuel System Components

The typical carbureted fuel system and related
components include the following:

• Fuel Tank

• Fuel Lines

• In-line Fuel Filter

• Fuel Pump

• Carburetor

Operation

The fuel from the tank is moved through the in-line
filter and fuel lines by the fuel pump. On engines not
equipped with a fuel pump, the fuel tank outlet is
located above the carburetor inlet allowing gravity to
feed fuel to the carburetor.

Fuel Recommendations

General Recommendations

Purchase gasoline in small quantities and store in
clean, approved containers. A container with a
capacity of 2 gallons or less with a pouring spout is
recommended. Such a container is easier to handle
and helps eliminate spillage during refueling.

• Do not use gasoline left over from the previous
season, to minimize gum deposits in your fuel
system and to ensure easy starting.

• Do not add oil to the gasoline.

• Do not overfill the fuel tank. Leave room for the
fuel to expand.

Fuel T y pe

For best results, use only clean, fresh, unleaded
gasoline with a pump sticker octane rating of 87 or
higher. In countries using the Research fuel rating
method, it should be 90 octane minimum.

Unleaded gasoline is recommended as it leaves less
combustion chamber deposits and reduces harmful
exhaust emissions. Leaded gasoline is not
recommended and must not be used on EFI engines,
or on other models where exhaust emissions are
regulated.

Gasoline/Alcohol blends

Gasohol (up to 10% ethyl alcohol, 90% unleaded
gasoline by volume) is approved as a fuel for Kohler
engines. Other gasoline/alcohol blends are not
approved.

5

Fuel then enters the carburetor float bowl and is
drawn into the carburetor body. There, the fuel is
mixed with air. This fuel-air mixture is then burned in
the engine combustion chamber.

Gasoline/Ether blends

Methyl Tertiary Butyl Ether (MTBE) and unleaded
gasoline blends (up to a maximum of 15% MTBE by
volume) are approved as a fuel for Kohler engines.
Other gasoline/ether blends are not approved.

5.1

Section 5
Fuel System and Governor

Fuel Filter

Most engines are equipped with an in-line filter.
Periodically inspect the filter and replace with a
genuine Kohler filter every 200 operating hours.

Fuel Line

In compliance with CARB Tier III Emission
Regulations, carbureted engines with a “Family”
identification number beginning with “6” or greater
(See Figure 5-1), must use Low Permeation SAE 30 R7
rated fuel line; certified to meet CARB requirements.
Standard fuel line may not be used. Order
replacement hose by part number through a Kohler
Engine Service Dealer.

IMPORTANT ENGINE INFORMATION
THIS ENGINE MEETS U.S. EPA AND CA 2005
AND LATER AND EC STAGE II (SN:4) EMISSION
REGS FOR SI SMALL OFF–ROAD ENGINES

FAMILY 6 KHXS.7252 PH
TYPE APP

DISPL. (CC)
MODEL NO.

N11236

SPEC. NO.
SERIAL NO.
BUILD DA TE
OEM PROD. NO.

EMISSION COMPLIANCE PERIOD:
EPA: CARB:
CERTIFIED ON:
REFER TO OWNER'S MANUAL FOR HP RATING,
SAFETY, MAINTENANCE AND ADJUSTMENTS

1-800-544-2444 www.kohlerengines.com

KOHLER CO. KOHLER, WISCONSIN USA

Figure 5-1. “Family” Number Location.

5.2

Section 5

Fuel System and Governor

Fuel System T est s

When the engine starts hard, or turns over but will not start, it is possible that the problem is in the fuel system.
To find out if the fuel system is causing the problem, perform the following tests.

Troubleshooting – Fuel System Related Causes

T est Conclusion

1. Check the following:
a. Make sure the fuel tank contains clean, fresh,

proper fuel.

b. Make sure the vent in fuel tank cap is open.

c. Make sure the fuel valve is open.

d. Make sure vacuum and fuel lines to fuel

pump are secured and in good condition.

2. Check for fuel in the combustion chamber.
a. Disconnect and ground spark plug leads.
b. Close the choke on the carburetor.

c. Crank the engine several revolutions.

d. Remove the spark plug and check for fuel at

the tip.

3. Check for fuel flow from the tank to the fuel

pump.

a. Remove the fuel line from the inlet fitting of

fuel pump.

b. Hold the line below the bottom of the tank.

Open the shut-off valve (if so equipped) and
observe flow.

4. Check the operation of fuel pump.
a. Remove the fuel line from the inlet fitting of

carburetor.

b. Crank the engine several times and observe

flow.

2. If there is fuel at the tip of the spark plug, fuel is

reaching the combustion chamber.

If there is no fuel at the tip of the spark plug,
check for fuel flow from the fuel tank (Test 3).

3. If fuel does flow from the line, check for faulty

fuel pump (Test 4).

If fuel does not flow from the line, check the fuel
tank vent, fuel pickup screen, in-line filter, shut­off valve, and fuel line. Correct any observed
problem and reconnect the line.

4. If fuel does flow from the line, check for faulty

carburetor. (Refer to the "Carburetor" portions of
this section).

If fuel does not flow from the line, check for a
clogged fuel line. If the fuel line is unobstructed,
check for overfilled crankcase and/or oil in pulse
line. If none of the checks reveal the cause of the
problem, replace the pump.

5

5.3

Section 5
Fuel System and Governor

Fuel Pump

General

These engines are equipped with a pulse type fuel
pump. The pumping action is created by the
oscillation of positive and negative pressures within
the crankcase. This pressure is transmitted to the pulse
pump through a rubber hose connected between the
pump and crankcase. The pumping action causes the
diaphragm on the inside of the pump to pull fuel in
on its downward stroke and to push it into the
carburetor on its upward stroke. Two check valves
prevent fuel from going backward through the pump.

Inlet Line

Outlet Line (to
Carburetor)

Pulse Line

Figure 5-2. Pulse Pump Connections.

Performance

Minimum fuel delivery rate must be 7.5 L/hr. (2 gal./
hr.) with a pressure at 0.3 psi and a fuel lift of 24 in. A

1.3 L/hr. (0.34 gal./hr.) fuel rate must be maintained at
5 Hz.

3. Remove the pulse line that connects the pump to
the crankcase.

4. Install a new pump using the hex flange screws.

NOTE: Make sure the orientation of the new

pump is consistent with the removed
pump. Internal damage may occur if
installed incorrectly.

5. Connect the pulse line between the pump and
crankcase.

6. Torque the hex flange screws to 2.3 N·m
(20 in. lb.).

7. Connect the fuel lines to the inlet and outlet
fittings.

Carburetor

General

CV17-740 engines in this series are equipped with
either a Nikki or Keihin one-barrel, fixed main jet
carburetor. Some applications use a fuel shut-off
solenoid installed in place of the fuel bowl retaining
screw, and also an accelerator pump. All carburetors
feature a self-relieving choke like or similar to the one
shown in the exploded view on page 5.12. These
carburetors include three main circuits, which
function as described following. CV750 engines use a
Keihin BK two-barrel carburetor on a matching intake
manifold. This carburetor with related servicing and
adjustments is covered beginning on page 5.20.

Replacing the Fuel Pump

Replacement pumps are available through your
source of supply. To replace the pulse pump follow
these steps. Note orientation of pump before
removing.

1. Disconnect the fuel lines from the inlet and outlet
fittings.

2. Remove the hex flange screws (securing pump)
and fuel pump.

5.4

CV17-740 Engines

Float Circuit: The fuel level in the bowl is maintained
by the float and fuel inlet needle. The buoyant force of
the float stops fuel flow when the engine is at rest.
When fuel is being consumed, the float will drop and
fuel pressure will push the inlet needle away from the
seat, allowing more fuel to enter the bowl. When
demand ceases, the buoyant force of the float will
again overcome the fuel pressure and stop the flow.

Section 5

Fuel System and Governor

Slow Circuit: (See Figure 5-3) At low speeds the engine operates only on the slow circuit. As a metered amount
of air is drawn through the slow air bleed jet, fuel is drawn through the main jet and further metered through the
slow jet. Air and fuel are mixed in the body of the slow jet and exit to the transfer port. From the transfer port
this air fuel mixture is delivered to the idle progression chamber. From the idle progression chamber the air fuel
mixture is metered through the idle port passage. At low idle when the vacuum signal is weak, the air fuel
mixture is controlled by the setting of the idle fuel adjusting screw. This mixture is then mixed with the main
body of air and delivered to the engine. As the throttle plate opening increases, greater amounts of air fuel
mixture are drawn in through the fixed and metered idle progression holes. As the throttle plate opens further
the vacuum signal becomes great enough so the main circuit begins to work.

Fuel Inlet

Float Valve Seat

Float Valve

Main Jet

Accelerator Pump Nozzle

Check Valve Spring

Leak Jet

Idle Speed
(RPM)
Adjustment
Screw

Float

Main Emulsion
Hole

Slow Air Bleed Jet

Main Air Bleed Jet

Choke Valve

Bowl Vent

Idle Progression
Chamber

Slow
Jet

Keihin Carburetors Only

Low (Idle) Mixture Screw

Spring

Idle Limiter Jet

Idle Port

Idle Limiter

Idle Port

Throttle Valve

Jet

Capped/Preset
Low (Idle)
Mixture Setting

Idle
Progression
Holes

5

Outlet Check Valve

Adjustment Screw

Diaphragm Spring

Pump Diaphragm

Air

Fuel

Mixture

Inlet Check Valve

Figure 5-3. Slow Circuit.

ACCELERAT OR PUMP

ASSEMBLY

(Some Carburetors)

Main Nozzle

Slow Passage Pipe

Main Jet

Fuel Shut-Off Solenoid
with Main Jet

5.5

Section 5
Fuel System and Governor

Main Circuit: (See Figure 5-4) At high speeds/loads the engine operates on the main circuit. As a metered
amount of air is drawn through the main air bleed jet, fuel is drawn through the main jet. The air and fuel are
mixed in the main nozzle and then enter the main body of airflow, where further mixing of the fuel and air takes
place. This mixture is then delivered to the combustion chamber. The carburetor has a fixed main circuit; no
adjustment is possible.

Air

Idle Speed
(RPM)
Adjustment
Screw

Fuel Inlet

Fuel

Mixture

Float Valve Seat

Float Valve

Main Jet

Accelerator Pump Nozzle

Check Valve Spring

Leak Jet

Outlet Check Valve

Adjustment Screw

Diaphragm Spring

Pump Diaphragm

Inlet Check Valve

Float

Main Emulsion
Hole

Main Air Bleed Jet

Choke Valve

Bowl Vent

ACCELERAT OR PUMP

ASSEMBLY

(Some Carburetors)

Throttle Valve

Main Nozzle

Main Jet

Fuel Shut-Off Solenoid
with Main Jet

Figure 5-4. Main Circuit.

5.6

Troubleshooting – Carburetor Related Causes

Condition Possible Cause/Probable Remedy

1. Engine starts hard, runs roughly
or stalls at idle speed.

2. Engine runs rich (indicated by
black, sooty exhaust smoke,
misfiring, loss of speed and power,
governor hunting, or excessive
throttle opening).

3. Engine runs lean (indicated by
misfiring, loss of speed and power,
governor hunting, or excessive
throttle opening).

4. Fuel leaks from carburetor.

1. Low idle fuel mixture/speed improperly adjusted. Adjust the low
idle speed screw, then adjust the low idle fuel needle.

2a. Clogged air cleaner. Clean or replace.

b. Choke partially closed during operation. Check the choke lever/

linkage to ensure choke is operating properly.

c. Low idle fuel mixture is improperly adjusted. Adjust low idle

fuel needle.

d. Float level too high. Separate fuel bowl from carburetor body.

Free (if stuck), or replace float.

e. Dirt under the fuel inlet needle. Remove needle; clean needle and

seat and blow with compressed air.

f. Bowl vent or air bleeds plugged. Remove low idle fuel adjusting

needle. Clean vent, ports, and air bleeds. Blow out all passages
with compressed air.

g. Leaky, cracked, or damaged float. Submerge float to check for

leaks.

3a. Low idle fuel mixture is improperly adjusted. Adjust low idle

fuel needle.

b. Float level too low. Separate fuel bowl from carburetor body. Free

(if stuck), or replace float.

c. Idle holes plugged; dirt in fuel delivery channels. Remove low

idle fuel adjusting needle. Clean main fuel jet and all passages;
blow out with compressed air.

4a. Float stuck. See Remedy 2d.

b. Dirt under fuel inlet needle. See Remedy 2e.

c. Bowl vents plugged. Blow out with compressed air.

d. Carburetor bowl gasket leaks. Replace gasket.

Section 5

Fuel System and Governor

5

Troubleshooting Checklist

When the engine starts hard, runs roughly or stalls at
low idle speed, check the following areas before
adjusting or disassembling the carburetor.

• Make sure the fuel tank is filled with clean, fresh
gasoline.

• Make sure the fuel tank cap vent is not blocked
and that it is operating properly.

• Make sure fuel is reaching the carburetor. This
includes checking the fuel shut-off valve, fuel
tank filter screen, in-line fuel filter, fuel lines and
fuel pump for restrictions or faulty components
as necessary.

• Make sure the air cleaner base and carburetor are
securely fastened to the engine using gaskets in
good condition.

• Make sure the air cleaner element (including the
precleaner if equipped) is clean, and all air
cleaner components are fastened securely.

• Make sure the ignition system, governor system,
exhaust system, and throttle and choke controls
are operating properly.

If the engine is hard-starting, runs roughly or stalls at
low idle speed, it may be necessary to service the
carburetor.

5.7

Section 5
Fuel System and Governor

High Altitude Operation

When operating the engine at altitudes of 1500 m
(5000 ft.) and above, the fuel mixture tends to get over­rich. This can cause conditions such as black, sooty
exhaust smoke, misfiring, loss of speed and power,
poor fuel economy, and poor or slow governor
response.

To compensate for the effects of high altitude, special
high altitude jet kits are available. The kits include a
new main jet, slow jet (where applicable), necessary
gaskets and O-Rings. Refer to the parts manual for the
correct kit number.

Fuel Shut-off Solenoid

Some carburetors are equipped with an optional fuel
shut-off solenoid. The solenoid is installed in place of
the bowl retaining screw. The solenoid has a spring­loaded pin that retracts when 12 volt current is
applied to the lead. When it is extended, the main fuel
jet is blocked, preventing normal carburetor operation.

Below is a simple test, made with the engine off, that
can determine if the solenoid is functioning properly:

1. Shut off the fuel and remove the solenoid from
the carburetor. When the solenoid is loosened
and removed, gas will leak out of the carburetor.
Have a container ready to catch the fuel. The
main jet is mounted in the tip of the solenoid pin.
Be careful that it does not get damaged while the
solenoid is separated from the carburetor.

2. Wipe the tip of the solenoid with a shop towel or
blow it off with compressed air, to remove any
remaining fuel. Take the solenoid to a location
with good ventilation and no fuel vapors present.
You will also need a 12 volt power source that can
be switched on and off.

3. Be sure the power source is switched “off”.
Connect the positive power source lead to the red
lead of the solenoid. Connect the negative power
source lead to the solenoid body.

4. Turn the power source “on” and observe the pin
in the center of the solenoid. The pin should
retract with the power “on” and return to its
original position with the power off. Test several
times to verify operation.

Fuel Shut-Off
Solenoid

Figure 5-5. Fuel Shut-off Solenoid Location.

Carburetor Adjustments (CV17-740)

General

The carburetor is designed to deliver the correct fuel­to-air mixture to the engine under all operating
conditions. The high speed mixture adjustment is set
at the factory and cannot be adjusted. The low idle
fuel adjusting needle (some models) is also set at the
factory and normally does not need adjustment.

Depending on model and application, engines may
also be equipped with a “Governed Idle System.” If
equipped with a “Governed Idle System”, refer to
“Models with Governed Idle System” when
performing any carburetor adjustment, as an
additional step to the listed adjustment procedure(s) is
required.

NOTE: Carburetor adjustments should be made only

after the engine has warmed up.

NOTE: Certified engines may have a fixed idle or

limiter cap on the idle fuel adjusting needle.
Do not attempt steps 1 and 2 below. Proceed
directly to step 3. Step 5 can only be
performed within the limits allowed by the
cap.

Adjusting Low Idle Fuel and Speed

To adjust the carburetor idle fuel and speed, see
Figure 5-6 and follow these steps.

1. With the engine stopped, turn the low idle fuel
adjusting needle (if equipped) in (clockwise) until
it bottoms lightly.

5.8

Section 5

Fuel System and Governor

NOTE: The tip of the idle fuel adjusting needle

is tapered to critical dimensions.
Damage to the needle and the seat in the
carburetor body will result if the needle
is forced.

Low Idle Fuel
Adjustment
(Some Models)

Low Idle Speed
(RPM) Adjustment

Figure 5-6. Carburetor Adjustments.

2. Preliminary Settings: Turn the adjusting needle
out (counterclockwise) from lightly bottomed

2-1/4 turns.

3. Start the engine and run at half throttle for 5 to 10
minutes to warm up. The engine must be warm
before making final settings. Check that the
throttle and choke plates can fully open.

NOTE: The carburetor has a self-relieving

choke. The choke plate and shaft
assembly is spring loaded. Check to
make sure the plate moves freely and is
not binding, affecting idle fuel delivery.

5. Low Idle Fuel Needle Setting: Place the throttle
into the “idle” or “slow” position. Turn the low
idle fuel adjusting needle in (slowly) until engine
speed decreases and then back out approximately
3/4 to 1 turn to obtain the best low speed
performance.

6. Recheck the idle speed using a tachometer and
readjust the speed as necessary.

Models with Governed Idle System

An optional governed idle control system is supplied
on some engines. The purpose of this system is to
maintain a desired idle speed regardless of ambient
conditions (temperature, parasitic load, etc.) that may
change. Engines with this feature contain a small
secondary spring connected between the governor
lever and the lower adjustment tab of the main
bracket. See Figure 5-7.

The system requires an additional procedure for
setting the idle speed. If speed adjustments are
required proceed as follows.

1. Make any necessary speed or control adjustments
following the appropriate instructions covered in
this section.

2. Move the throttle control to the idle position.
Hold the governor lever away from the
carburetor, or hold the throttle lever so it is tight
against the idle speed adjusting screw, to negate
the governor activation. See Figure 5-8. Check the
speed with a tachometer and adjust it to 1500
RPM.

5

4. Low Idle Speed Setting: Place the throttle control
into the “idle” or “slow” position. Set the low
idle speed to 1200 RPM* (± 75 RPM) by turning
the low idle speed adjusting screw in or out.
Check the speed using a tachometer.

*NOTE: The actual low idle speed depends on

the application. Refer to the equipment
manufacturer’s recommendations. The
low idle speed for basic engines is 1200
RPM. To ensure best results when setting
the low idle fuel needle, the low idle
speed should be 1200 RPM (± 75 RPM).

3. Release the governor lever and allow the engine
to return to the governed idle speed. Check it
with a tachometer against the equipment
manufacturers recommended idle speed.
Governed Idle Speed (RPM) is typically 300 RPM
(approximate) higher than the low idle speed. If
adjustment is necessary, bend the adjusting tab on
the speed control assembly to set. See Figure 5-7.

5.9

Section 5
Fuel System and Governor

Governed
Idle Spring

Figure 5-7. Governed Idle Spring Location.

5. Slide the carburetor off the retaining studs.
Remove the fuel bowl retaining screw or fuel
shut-off solenoid and drain the fuel into a safe
container. Remove the bowl from the carburetor
body.

Tab

16.5 mm
(0.65 in.)

Hold Throttle
Lever Against
Screw

Figure 5-8. Holding Throttle Lever Against Idle
Stop Screw (One-Barrel Carburetor).

Carburetor Servicing (CV17-740)

Nikki Carburetors

Float Replacement

If symptoms described in the carburetor
troubleshooting guide indicate float level problems,
remove the carburetor from the engine to check and/or
replace the float. Use a float kit to replace float, pin
and inlet needle or valve.

1. Remove the air cleaner and air intake components
from the carburetor as described in Section 4.

T urn Carburetor
Upside Down

Figure 5-9. Proper Float Level.

6. Turn the carburetor body upside down and check
the float level as shown in Figure 5-9. With the
float needle valve fully seated, 16.5 mm (0.65 in.)
should be measured from the body to the float as
indicated. Don’t attempt to adjust by bending the
tab; replace the float with a kit if the level is
wrong.

7. Pull the float hinge pin and remove the float with
the inlet needle attached to inspect the needle and
seat. If dirty, blow out with compressed air.
Replace the float components as needed with the
kit.

8. Using new gaskets, reinstall the bowl and tighten
the bowl retaining screw or solenoid to

5.1-6.2 N·m (45-55 in. lb.).

9. Reinstall the carburetor on the engine, reconnect
the fuel line, control linkages and air intake
components. Retest operation.

2. Disconnect the fuel inlet line from the carburetor.

3. Disconnect governor/throttle linkage from the
carburetor.

4. Disconnect lead wires from fuel solenoid­equipped carburetor.

5.10

Section 5

Fuel System and Governor

Disassembly

Use the carburetor repair kit (and the float repair kit if
float components are to be replaced). Refer to Figure
5-10 for parts identification. The Kohler part number
and the Nikki lot number are stamped on the choke
side flange on top of the carburetor body. Refer to the
parts manual for the carburetor involved to ensure the
correct repair kits and replacement parts are used.
Disassemble carburetor as follows after removal from
the engine. See Figure 5-10.

1. Remove the fuel bowl retaining screw or solenoid
assembly, then remove the bowl and bowl gasket.
On solenoid-equipped carburetors, the main jet is
mounted in the tip of the solenoid pin. Be careful
that it does not get damaged while the solenoid is
separated from the carburetor.

2. Pull the float hinge pin, and remove the float with
the inlet needle attached.

3. Remove the vent plug from the column on fuel
solenoid-equipped carburetors.

4. Remove the screws holding the throttle plate to
the throttle shaft, pull the throttle shaft from the
carburetor body.

5. Remove the screws securing the choke plate to
the choke shaft assembly and pull the choke shaft
assembly out of the carburetor body. Disassemble
the self-relieving parts from shaft as needed.

6. Remove the three screws holding the passage
cover to the body, remove the cover gasket.

7. Remove the idle fuel adjusting needle and spring
if it does not have a limiter. Remove the idle
speed screw and spring. Except for the slow jet
nozzle, main jet, and emulsion tubes, which are
considered non-serviceable, the carburetor is now
completely disassembled and ready for thorough
inspection and cleaning.

5

5.11

Section 5
Fuel System and Governor

17

19

18

20

21

22

24

23

26

14

15

25

10

6

1. Carburetor Body

2. Idle Fuel Adjusting Screw*

3. Idle Fuel Adjusting Spring*

4. Passage Cover

5. Cover Gasket*

6. Cover Retaining Screw

5

7. Main Jet

8. Ground Lead (Solenoid only)

9. Fuel Bowl Gasket

10. Float Kit

11. Fuel Bowl

12. Bowl Retaining Screw Gasket

13. Bowl Retaining Screw

14. Shut-off Solenoid Assembly

15. Throttle Shaft/Lever

16. Throttle Plate

17. Choke Shaft

18. Choke Plate

19. Air Filter

20. Collar

21. Spring

22. Ring

23. Choke Lever

24. Idle Speed Screw

25. Idle Speed Spring

26. Setscrews (Plates - 4)

4

2

3

1

7

8

16

9

or

13

Figure 5-10. T ypical Carburetor - Exploded View.

Inspection/Repair

To clean vent ports, seats etc., use a good
commercially available carburetor solvent, such as
Gumout™, and clean, dry compressed air to blow out
internal channels and ports. Use a suitable shop rag to
prevent debris from hitting someone.

Carefully inspect all components and replace those
that are worn or damaged.

• Inspect the carburetor body for cracks, holes and
other wear or damage.

11

12

*Included in Carburetor Repair Kit.

• Inspect the float for cracks, holes, and missing or
damaged float tabs. Check the float hinge and
shaft for wear or damage.

• Inspect the fuel inlet needle and seat for wear or
damage.

• Inspect the tip of the low idle fuel adjusting
needle (if equipped), for wear or grooves.

• The choke plate is spring loaded. Check to make
sure it moves freely.

5.12

Always use new gaskets when servicing or reinstalling
carburetors. Repair kits are available which include
new gaskets and other components. Service/repair kits
available for Nikki carburetors and affiliated
components are:

Carburetor Repair Kit
Float Kit
High Altitude Kit (1525-3048 m/5,000-10,000 ft.)
High Altitude Kit (Over 3048 m/10,000 ft.)
Solenoid Assembly Kit

Reassembly Procedure

Reassembly is essentially the reverse of the
disassembly procedure. Use new gaskets, springs and
adjusting screws as provided in the carburetor repair
kit. Also use new carburetor and intake manifold
gaskets. Set the idle speed (RPM) adjusting screw (if
equipped) 2-1/4 turns open for initial adjustment and
make final adjustments as described earlier.

Keihin Carburetors (CV17-740)

Section 5

Fuel System and Governor

Figure 5-12. Removing Float and Inlet Needle.

3. Clean the carburetor bowl and inlet seat areas as
required, before installation of new parts.

4. Attach the inlet needle to the metal tang of the
float with the wire clip. The formed 90° lip of the
metal tang should point up, with the needle valve
hanging down. See Figure 5-13.

5

Float Replacement

1. Clean the exterior surfaces of dirt or foreign
material before disassembling the carburetor.
Unseat the clamp and disconnect the accelerator
pump hose (if so equipped), from the upper
fitting. Remove the four fuel bowl screws and
carefully separate the fuel bowl from the
carburetor. Do not damage the O-Ring(s).
Transfer any remaining fuel into an approved
container. Save all parts. See Figure 5-11.

Figure 5-13. Float and Inlet Needle.

5. Install the float and inlet needle down into the
seat and carburetor body. Insert the new pivot pin
through the float hinge and secure with the new
retaining screw. See Figure 5-14.

Figure 5-11. Fuel Bowl Removed from Carburetor.

2. Remove the float pin screw and lift out the old
float, pin, and inlet needle. See Figure 5-12.
Discard all of the parts. The seat for the inlet
needle is not serviceable, and should not be
removed.

5.13

Section 5
Fuel System and Governor

Figure 5-14. Installing Float Assembly.

6. Hold the carburetor body so the float assembly
hangs vertically and rests lightly against the fuel
inlet needle. The inlet needle should be fully
seated but the center pin of the needle (on
retainer clip end) should not be depressed. Check
the float height adjustment.

NOTE: The inlet needle center pin is spring loaded.

Make sure the float assembly rests against the
fuel inlet needle without depressing the
center pin.

7. The correct float height adjustment is 12.0 mm
(0.472 in.) measured from the float bottom to the
body of the carburetor. See Figure 5-15. Adjust
the float height by carefully bending the metal
tang of the float.

8. When the proper float height is obtained,
carefully reinstall the fuel bowl, with the
O-Ring(s) in place, onto the carburetor. Secure
with the four original screws. Torque the screws
to 2.5 ± 0.3 N·m (23 ± 2.6 in. lb.). Reattach the
accelerator pump hose (if so equipped), and
secure with the clip. See Figure 5-16.

Figure 5-16. Installing Fuel Bowl.

Disassembly/Overhaul

1. Clean the exterior surfaces of dirt or foreign
material before disassembling the carburetor.
Unseat the clamp and disconnect the accelerator
pump hose (if so equipped), from the upper
fitting. Remove the four fuel bowl screws and
separate the fuel bowl from the carburetor.
Transfer any remaining fuel into an approved
container. Remove and discard the old O-Ring(s).
See Figure 5-17.

Figure 5-15. Checking Float Height.

NOTE: Be sure to measure from the casting

surface, not the rubber gasket, if still
attached.

5.14

Figure 5-17. Fuel Bowl Removed from Carburetor.

NOTE: Further disassembly of fuel bowl is not

necessary unless the Accelerator Pump Kit
24 757 47-S, or Fuel Solenoid Kit 24 757 45-S
(obtained separately), are also being installed.

Section 5

Fuel System and Governor

2. Remove the float pin screw and lift out the old
float, pin, and inlet needle. See Figure 5-18.
Discard all of the parts. The seat for the inlet
needle is not serviceable, and should not be
removed.

Figure 5-18. Removing Float and Inlet Needle.

3. Remove and discard the round plug from the
bottom of the slow jet tower of the carburetor
body. Use an appropriate size flat screwdriver,
and carefully remove the slow and main jets from
the carburetor. After the main jet has been
removed, the main nozzle can be taken out
through the bottom of the main tower. Save the
parts for cleaning and reuse. See Figure 5-19.

NOTE: The carburetor is now disassembled for

appropriate cleaning and installation of
the parts in the overhaul kit. Further
disassembly is not necessary. The
throttle shaft assembly, fuel inlet seat,
and bowl chamber baffle, are non­serviceable items and should not be
removed. The choke shaft assembly is
serviceable, however it should not be
removed unless a Choke Repair Kit
24 757 36-S will be installed.

6. Clean the carburetor body, jets, vent ports, seats,
etc., using a good commercially available
carburetor solvent. Use clean, dry compressed air
to blow out the internal channels and ports.
Inspect and thoroughly check the carburetor for
cracks, wear, or damage. Inspect the fuel inlet seat
for wear or damage. Check the spring loaded
choke plate to make sure it moves freely on the
shaft.

7. Clean the carburetor float bowl as required. If it
has an accelerator pump that is not being serviced
at this time, prevent the cleaning solvent from
contacting the check valve and accelerator pump
components.

8. Install the main nozzle and the main jet into the
tower of the carburetor body. See Figure 5-20.

5

Figure 5-19. Main Jet and Slow Jet Removed.

4. Remove the two screws securing the top cover,
gasket, and ground lead (fuel solenoid-equipped
models). Discard the gasket and screws only.

5. Remove the idle speed and idle fuel adjusting
screws and springs from the carburetor. Discard
the parts.

Figure 5-20. Installing Main Nozzle and Main Jet.

9. Install the slow jet and new plug into end of slow
jet tube. See Figures 5-21 and 5-22.

5.15

Section 5
Fuel System and Governor

Figure 5-21. Installing Slow Jet.

11. Install the float and inlet needle down into the
seat and carburetor body. Insert the new pivot pin
through the float hinge and secure with the new
retaining screw. See Figure 5-24.

Figure 5-24. Installing Float Assembly .

Figure 5-22. Installing Plug into Slow Jet Tube.

10. Attach the inlet needle to the metal tang of the
float with the wire clip. The formed 90° lip of the
metal tang should point up, with the needle valve
hanging down. See Figure 5-23.

12. Hold the carburetor body so the float assembly
hangs vertically and rests lightly against the fuel
inlet needle. The inlet needle should be fully
seated but the center pin of the needle (on
retainer clip end) should not be depressed. Check
the float height adjustment.

NOTE: The inlet needle center pin is spring

loaded. Make sure the float assembly
rests against the fuel inlet needle,
without depressing the center pin.

13. The correct float height adjustment is 12.0 mm
(0.472 in.) measured from the float bottom to the
body of the carburetor. See Figure 5-25. Adjust
the float height by carefully bending the metal
tang of the float.

Figure 5-23. Float and Inlet Needle.

5.16

Figure 5-25. Checking Float Height.

14. When the proper float height is obtained,
carefully install the new O-Rings for the fuel
bowl and the accelerator pump transfer passage
(if so equipped). See Figure 5-26.

Section 5

Fuel System and Governor

Figure 5-28. Installing Idle Fuel Adjusting Screw
and Spring.

Figure 5-26. Installing Fuel Bowl O-Rings.

15. Install the fuel bowl onto the carburetor. Secure
with the four original screws. Torque the screws
to 2.5 ± 0.3 N·m (23 ± 2.6 in. lb.). Reattach the
accelerator pump hose (if so equipped), and
secure with the clip. See Figure 5-27.

Figure 5-27. Installing Fuel Bowl.

16. Install the new cover gasket and top cover on the
carburetor. Secure with the two large-head screws
and attach the ground lead (if equipped with a
fuel solenoid), to the original screw location.
Torque the top cover screws to 2.5 ± 0.3 N·m
(23 ± 2.6 in. lb.).

17. Place the longer new spring onto the idle fuel
adjusting screw and install it into the carburetor.
As an initial adjustment, set to 1 turn out from
lightly seated. See Figure 5-28.

18. Place the shorter new spring onto the idle speed
adjusting screw and install it into the carburetor.
Thread in until 3 or 4 threads are exposed, as an
initial adjustment. See Figure 5-29.

Figure 5-29. Installing Idle Speed Adjusting Screw
and Spring.

Accelerator Pump Rebuild

NOTE: Access to the accelerator pump can be

limited, due to specific engine options or the
application. Although installation of the kit is
possible with the carburetor intact, removal is
normally necessary and recommended. These
instructions cover installation of the kit
components only. If needed, instructions for
removal and reinstallation of the carburetor
can be found in Sections 9 and 11
respectively.

1. Remove the vacuum hose from the accelerator
pump cover and the carburetor flange fitting.

5

5.17

Section 5
Fuel System and Governor

2. Remove the three screws securing the cover to the
accelerator pump housing. Remove the cover,
spring, and diaphragm. See Figure 5-30.

Figure 5-32. Check Valve and Ret aining Ring
Installed.

Figure 5-30. Accelerator Pump Cover and
Diaphragm Removed.

3. Remove the retaining ring over the rubber check
valve, using a snap ring pliers. Remove the check
valve from the fuel delivery chamber. See Figure
5-31.

Figure 5-31. Removing Retaining Ring.

4. Clean the accelerator pump housing and cover as
required.

5. Install the new check valve into the fuel delivery
chamber. Secure with the new retaining ring. See
Figure 5-32.

6. Notice the small alignment tab and the small
bead on one side of the outer diameter of the new
diaphragm. Install the diaphragm into the
housing, so the alignment tab is in the small
notch, the bead is down in the recessed channel,
and the “donut” around the metal center plate
should be out, facing you. See Figure 5-33.

Figure 5-33. Diaphragm Installed.

7. Install the new diaphragm spring and reinstall
the accelerator pump cover. Secure with the three
new screws. Torque the screws to 2.0 ± 0.6 N·m
(18.2 ± 5.2 in. lb.). See Figure 5-34.

5.18

Figure 5-34. Installing Accelerator Pump Housing
Screws and Hose.

Section 5

Fuel System and Governor

5. Use a screw extractor (easy out) and remove the
original choke shaft bushing with the old choke
lever from the carburetor housing. Save the
bushing to use as a driver for installing the new
bushing. Discard the old lever.

6. Clean the I.D. of both choke shaft bores as
required.

7. Insert the new bushing through the new choke
lever from the outside, and start the bushing in
the outer shaft bore. Position the choke lever so
that the protruding boss on the carburetor
housing is between the two stops formed in the
choke lever. See Figure 5-36.

8. Install the new clips onto each end of the new
vacuum hose, and connect the hose onto the
fittings. See Figure 5-34. Discard all the old parts.

Choke Repair

1. Remove the carburetor from the engine. Discard
the old mounting gaskets for the air cleaner and
carburetor.

2. Clean the areas around the choke shaft and the
self-relieving choke mechanism thoroughly.

3. Remove and discard the plastic cap from the end
of the choke lever/shaft assembly.

4. Note the position of the spring legs and the choke
plate for correct reassembly later. See Figure
5-35. Remove the two screws attaching the choke
plate to the choke shaft. Pull the shaft out of the
carburetor body and discard the removed parts.

5

Figure 5-36. Assembling Choke Lever .

8. Turn the old bushing upside down and use it as a
driver to carefully press or tap the new bushing
into the carburetor body until it bottoms. Check
that the choke lever pivots freely without
restriction or binding. See Figure 5-37.

Figure 5-35. Choke Details.

Figure 5-37. Installing Bushing.

5.19

Section 5
Fuel System and Governor

9. Install the new return spring onto the new choke
shaft, so the upper leg of the spring is between
the two formed “stops” on the end of the choke
shaft. See Figure 5-38. Note: Make sure it stays in
this location during the following step.

Figure 5-38. Choke Shaft and Spring Det ails.

10. Slide the choke shaft and spring, into the
carburetor. Pivot (preload) the shaft and set the
inner leg of the spring, against the formed stop
within the choke lever as originally assembled.
See Figure 5-35. The opposing leg of the spring
must still be between the formed “stops” of the
choke shaft.

11. Place a drop of the Loctite® on the threads of each
new screw. Install the new choke plate to the flat
side of the choke shaft and start the two screws.
The larger cutout must be on the right. Close the
choke and check the plate alignment within the
carburetor throat, then tighten the screws
securely. Do not overtighten.

12. Check for proper operation and free movement of
the parts. Install the new cap.

Always use new gaskets when servicing or reinstalling
carburetors. Repair kits are available which include
new gaskets and other components. Service/repair kits
available for Keihin carburetors and affiliated
components are:

Carburetor Repair Kit
Float Kit
Solenoid Assembly Kit
Accelerator Pump Kit
Choke Repair Kit
High Altitude Kit (1525-3048 m/5,000-10,000 ft.)
High Altitude Kit (Over 3048 m/10,000 ft.)

Carburetor

Keihin BK T wo-Barrel Carburetor (CV750)

The carburetor used on CV750 engines is a Keihin
two-barrel side draft design with fixed main jets. See
Figure 5-39. A self-relieving choke similar to that used
on single venturi carburetors is also contained in the
design. The circuits within the carburetor function as
described following:

Float Circuit:

The fuel level in the bowl is maintained by the float
and fuel inlet needle. The buoyant force of the float
stops fuel flow when the engine is at rest. When fuel is
being consumed, the float will drop and fuel pressure
will push the inlet needle away from the seat,
allowing more fuel to enter the bowl. When demand
ceases, the buoyant force of the float will again
overcome the fuel pressure, rising to the
predetermined setting and stop the flow.

Slow & Mid-Range Circuit:

At low speeds the engine operates only on the slow
circuit. As a metered amount of air is drawn through
the slow air bleed jets, fuel is drawn through the two
main jets and further metered through the slow jets.
Air and fuel are mixed in the body of the slow jet and
exit to the transfer port. From the transfer port the air
fuel mixture is delivered to the idle progression
chamber. From the idle progression chamber the air
fuel mixture is metered through the idle port
passages. At low idle when the vacuum signal is weak,
the air/fuel mixture is controlled by the setting of the
idle fuel adjusting screws. This mixture is then mixed
with the main body of air and delivered to the engine.
As the throttle plate opening increases, greater
amounts of air/fuel mixture are drawn in through the
fixed and metered idle progression holes. As the
throttle plate opens further the vacuum signal
becomes great enough so the main circuit begins to
work.

Main (High-Speed) Circuit:

At high speeds/loads the engine operates on the main
circuit. As a metered amount of air is drawn through
the four air jets, fuel is drawn through the main jets.
The air and fuel are mixed in the main nozzles and
then enter the main body of airflow, where further
mixing of the fuel and air occurs. This mixture is then
delivered to the combustion chamber. The carburetor
has a fixed main circuit; no adjustment is possible.

5.20

Section 5

Fuel System and Governor

Adjustment

NOTE: Carburetor adjustments should be made only

after the engine has warmed up.

The carburetor is designed to deliver the correct fuel­to-air mixture to the engine under all operating
conditions. The main fuel jet is calibrated at the
factory and is not adjustable*. The idle fuel adjusting
needle is also set at the factory and normally does not
need adjustment.

Depending on model and application, engines may
also be equipped with a “Governed Idle System.” If
equipped with a “Governed Idle System”, refer to
“Models with Governed Idle System” when
performing any carburetor adjustment, as an
additional step to the listed adjustment procedure(s) is
required.

*NOTE: Engines operating at altitudes above

approximately 1500 m (5000 ft.) may require
a special ‘‘high altitude’’ main jet. Refer to
‘‘High Altitude Operation’’.

If, however, the engine is hard-starting or does not
operate properly, it may be necessary to adjust or
service the carburetor.

Low Idle Fuel Adjusters
(with Limiters)

Low Idle Speed (RPM)
Adjustment Screw

*NOTE: The actual low idle speed depends on the

application. Refer to the equipment
manufacturer’s recommendations. The low
idle speed for basic engines is 1200 RPM. To
ensure best results when setting the low idle
fuel needle, the low idle speed should be
1200 RPM (± 75 RPM).

Low Idle Fuel Adjustment

NOTE: Engines will have fixed low idle or limiter

caps on the two idle fuel adjusting needles.
Step 3 can only be performed within the
limits allowed by the cap. Do not attempt to
remove the limiter caps.

1. Start the engine and run at half throttle for 5 to 10
minutes to warm up. The engine must be warm
before doing steps 2, 3, and 4.

2. Place the throttle control into the “idle” or
“slow” position. Adjust the low idle speed to

1200 RPM*. Follow the “Adjusting the Low Idle
Speed (RPM)” procedure.

3. Low Idle Fuel Needle(s) Setting: Place the
throttle into the “idle” or “slow” position.

a. Turn one of the low idle fuel adjusting needles

out (counterclockwise) from the preliminary
setting until the engine speed decreases
(rich). Note the position of the needle. Now
turn the adjusting needle in (clockwise). The
engine speed may increase, then it will
decrease as the needle is turned in (lean). Note
the position of the needle. Set the adjusting
needle midway between the rich and lean
settings. See Figure 5-40.

5

Fuel Solenoid

Bowl Drain Screw

Figure 5-39. Keihin T wo-Barrel Carburetor.

Carburetor Adjustment

Low Idle Speed (RPM) Adjustment

1. Low Idle Speed (RPM) Setting: Place the throttle
control into the “idle” or “slow” position. Set the
low idle speed to 1200 RPM* (± 75 RPM) by
turning the low idle speed adjusting screw in or
out. Check the speed using a tachometer.

b. Repeat the procedure on the other low idle

adjustment needle.

4. Recheck/adjust the Low Idle Speed (RPM), to the

specified setting.

5.21

Section 5
Fuel System and Governor

Adjust to

Lean

Midpoint

Rich

Left Side Right Side

Figure 5-40. Optimum Low Idle Fuel Settings.

Adjust to
Midpoint

Rich

Lean

Models with Governed Idle System

An optional governed idle control system is supplied
on some engines. The purpose of this system is to
maintain a desired idle speed regardless of ambient
conditions (temperature, parasitic load, etc.) that may
change. Engines with this feature contain a small
secondary spring connected between the governor
lever and the lower adjustment tab of the main
bracket. See Figure 5-41.

The system requires an additional procedure for
setting the idle speed. If speed adjustments are
required proceed as follows.

Governed
Idle Spring

Tab

Figure 5-41. Governed Idle Spring Location.

Hold
Throttle
Lever
Against
Screw

1. Make any necessary speed or control adjustments
following the appropriate instructions covered in
this section.

2. Move the throttle control to the idle position.
Hold the governor lever away from the
carburetor, or hold the throttle lever so it is tight
against the idle speed adjusting screw, to negate
the governor activation. See Figure 5-42. Check
the speed with a tachometer and adjust it to 1500
RPM.

3. Release the governor lever and allow the engine
to return to the governed idle speed. Check it
with a tachometer against the equipment
manufacturers recommended idle speed.
Governed Idle Speed (RPM) is typically 300 RPM
(approximate) higher than the low idle speed. If
adjustment is necessary, bend the adjusting tab on
the speed control assembly to set. See Figure 5-41.

Figure 5-42. Holding Throttle Lever Against Idle
Stop Screw (Two-Barrel Carburetor).

Carburetor Servicing

Float Replacement

If symptoms described in the carburetor
troubleshooting guide indicate float level problems,
remove the carburetor from the engine to check and/
or replace the float. Use a float kit to replace the float,
pin, float valve, clip and screw.

1. Perform the removal procedures for the Heavy
Duty Air Cleaner and Carburetor outlined in
Section 9 “Disassembly.”

2. Clean the exterior surfaces of dirt or foreign
material before disassembling the carburetor.
Remove the four mounting screws and carefully
separate the fuel bowl from the carburetor. Do
not damage the inner or bowl O-Ring. Transfer
any remaining fuel into an approved container.
Save all parts. Fuel can also be drained prior to
bowl removal by loosening/removal of the bowl
drain screw. See Figure 5-43.

5.22

Fuel Bowl

Bowl Drain Screw

Section 5

Fuel System and Governor

Figure 5-43. Fuel Bowl Removed From Carburetor.

3. Remove the float pin screw and lift out the old
float, pin and inlet needle. See Figure 5-44.
Discard all of the parts. The seat for the inlet
needle is not serviceable, and should not be
removed.

Figure 5-44. Removing Float and Inlet Needle.

4. Clean the carburetor bowl and inlet seat areas as
required, before installing the new parts.

5. Attach the inlet needle to the plastic tang of the
float with the wire clip. The formed 90° lip
should point up, with the needle valve hanging
down. See Figure 5-45.

Figure 5-45. Float and Inlet Needle Details.

6. Install the float and inlet needle down into the
seat and carburetor body. Install the new pivot
pin through the float hinge and secure with the
new retaining screw. See Figure 5-46.

Figure 5-46. Installing Float Assembly.

7. Hold the carburetor body so the float assembly
hangs vertically and rests lightly against the fuel
inlet needle. The inlet needle should be fully
seated but the center pin of the needle (on
retainer clip end) should not be depressed. Check
the float height adjustment.

NOTE: The inlet needle center pin is spring loaded.

Make sure the float rests against the fuel inlet
needle without depressing the center pin.

5

8. The correct float height setting is 17 mm
(0.669 in.) ± 1.5 mm (0.059 in.), measured from

the float bottom to the body of the carburetor. See
Figure 5-47. Replace the float if the height is
different than the specified setting. Do not
attempt to adjust by bending float tab.

5.23

Section 5
Fuel System and Governor

Fuel Bowl

Bowl Drain Screw

Figure 5-47. Checking Float Height.

NOTE: Be sure to measure from the casting

surface, not the rubber gasket, if still
attached.

9. When the proper float height is obtained,
carefully reinstall the fuel bowl, using new
O-Rings onto the carburetor. Secure with the four
original screws. Torque the screws to 2.5 ± 0.3
N·m (23 ± 2.6 in. lb.). See Figure 5-48.

Figure 5-49. Fuel Bowl Removed From Carburetor.

NOTE: Further disassembly of the fuel bowl is

not necessary unless the Fuel Solenoid
Kit, or Fuel Bowl Kit (obtained
separately), will also be installed.

2. Remove the float pin screw and lift out the old
float, pin, and inlet needle. See Figure 5-50.
Discard all the old parts. The seat for the inlet
needle is not serviceable, and should not be
removed.

Figure 5-48. Installing Fuel Bowl.

10. Install the carburetor and the heavy-duty air
cleaner as outlined in Section 11 “Reassembly.”

Disassembly/Overhaul

1. Clean the exterior surfaces of dirt or foreign
material before disassembling the carburetor.
Remove the four mounting screws and separate
the fuel bowl from the carburetor. Transfer any
remaining fuel into an approved container.
Remove and discard the old O-Rings. Fuel can
also be drained prior to bowl removal by
loosening/removal of the bowl drain screw. See
Figure 5-49.

5.24

Figure 5-50. Removing Float and Inlet Needle.

3. Use an appropriate size flat screwdriver, and
carefully remove the two main jets from the
carburetor. Note and mark the jets by location for
proper reassembly. The main jets may be size/side
specific. After the main jets are removed, the
main nozzles can be removed out through the
bottom of the main towers. Note the orientation/
direction of the nozzles. The end with the two
raised shoulders should be out/down adjacent to
the main jets. Save the parts for cleaning and
reuse. See Figure 5-51.

Section 5

Fuel System and Governor

Slow (Idle Fuel) Jets

Main Nozzles

Main Jets

Figure 5-51. Main Jets and Nozzles Removed.

4. Remove the screw securing the flat washer and
ground lead (if equipped), from the top of the
carburetor; then carefully pull (lift) out the two
slow jets. The slow jets may be size/side specific,
mark or tag for proper reassembly. Note the small
O-Ring on the bottom of each jet. See Figure 5-52
and 5-53. Save parts for cleaning and reuse unless
a Jet Kit is also being installed. Clean the slow jets
using compressed air. Do not use wire or
carburetor cleaner.

Figure 5-52. Removing Screw and Washer .

O-Ring

Figure 5-53. Slow Jets and O-Ring Detail.

5. Remove the idle speed (RPM) adjustment screw
and spring from the carburetor. Discard the parts.

NOTE: The carburetor is now disassembled for

appropriate cleaning and installation of the
parts in the overhaul kit. Further disassembly
is not necessary. The throttle shaft assembly,
fuel inlet seat, idle fuel adjustment screws
with limiter, and carburetor body, are non­serviceable items and should not be removed.
The choke shaft assembly is serviceable,
however it should not be removed unless a
Choke Repair Kit will be installed.

6. Clean the carburetor body, main jets, vent ports,
seats, etc. using a good commercially available
carburetor solvent. Keep away from plastic or
rubber parts if non-compatible. Use clean, dry
compressed air to blow out the internal channels
and ports. Do not use metal tools or wire to clean
orifices and jets. Inspect and thoroughly check
the carburetor for cracks, wear, or damage.
Inspect the fuel inlet seat for wear or damage.
Check the spring loaded choke plate to make sure
it moves freely on the shaft.

5

7. Clean the carburetor fuel bowl as required.

8. Install the two main nozzles into the towers of the
carburetor body. The end of the main nozzles
with the two raised shoulders should be out/
down (adjacent to the main jets). Make sure the
nozzles are completely bottomed. Carefully
install the main jets into the towers of the
carburetor body on the appropriate side, as
identified when removal was performed. See
Figure 5-54.

5.25

Section 5
Fuel System and Governor

Nozzle End with Two
Shoulders (Out/Down)

Main Jets

Figure 5-54. Installing Main Nozzles and Main Jets.

9. Make sure the O-Ring near the bottom of each
slow jet is new, or in good condition. Align and
insert the two slow jets into the top of carburetor.
See Figure 5-53.

10. Install the large flat retaining washer and secure
with the mounting screw, attaching the ground
lead if originally secured by the screw.

11. Install the new idle speed (RPM) adjustment
screw and spring onto the carburetor. Thread in
until 3 or 4 threads are exposed, as an initial
adjustment. See Figure 5-55.

Figure 5-56. Float and Inlet Needle Details.

13. Install the float and inlet needle down into the
seat and carburetor body. Install the new pivot
pinthrough the float hinge and secure with the
new retaining screw. See Figure 5-57.

Figure 5-57. Installing Float Assembly .

14. Hold the carburetor body so the float assembly
hangs vertically and rests lightly against the fuel
inlet needle. The inlet needle should be fully
seated but the center pin of the needle (on
retainer clip end) should not be depressed. Check
the float height adjustment.

Figure 5-55. Installing Idle Speed Adjusting Screw
and Spring.

12. Attach the inlet needle to the plastic tang of the
float with the wire clip. The formed 90° lip
should point up, with the needle valve hanging
down. See Figure 5-56.

5.26

NOTE: The inlet needle center pin is spring

loaded. Make sure the float rests against
the fuel inlet needle without depressing
the center pin.

15. The correct float height setting is 17 mm
(0.669 in.) ± 1.5 mm (0.059 in.), measured from
the float bottom to the body of the carburetor. See
Figure 5-58. Replace the float if the height is
different than the specified setting. Do not
attempt to adjust by bending float tab.

Figure 5-58. Checking Float Height.

NOTE: Be sure to measure from the casting surface,

not the rubber gasket, if still attached.

Section 5

Fuel System and Governor

4. Note the position of the spring legs and the choke
plate for correct reassembly later. See Figure
5-60. Remove the two screws attaching the choke
plate to the choke shaft. Pull the shaft out of the
carburetor body and discard the removed parts.

5

16. When the proper float height is obtained, carefully
reinstall the fuel bowl, using new O-Rings onto
the carburetor. Secure with the four original
screws. Torque the screws to 2.5 ± 0.3 N·m
(23 ± 2.6 in. lb.). See Figure 5-59.

Figure 5-59. Installing Fuel Bowl.

Choke Repair

1. Remove the carburetor from the engine. Discard
the old mounting gaskets for the air cleaner and
carburetor.

Figure 5-60. Choke Details.

5. Use a screw extractor (easy-out) and remove the
original choke shaft bushing with the old choke
lever from the carburetor housing. Save the
bushing to use as a driver for installing the new
bushing. Discard the old lever.

6. Clean the I.D. of both choke shaft bores as
required.

7. Insert the new bushing through the new choke
lever from the outside, and start the bushing in
the outer shaft bore. Position the choke lever so
the protruding boss on the carburetor housing is
between the two stops formed in the choke lever.
See Figure 5-61.

Stops

2. Clean the areas around the choke shaft and the
self-relieving choke mechanism thoroughly.

3. Remove and discard the plastic cap from the end
of the choke lever/shaft assembly.

Boss

Figure 5-61. Assembling Choke Lever .

5.27

Section 5
Fuel System and Governor

8. Turn the old bushing upside down and use it as a
driver to carefully press or tap the new bushing
into the carburetor body until it bottoms. Check
that the choke lever pivots freely without
restriction or binding. See Figure 5-62.

Figure 5-62. Installing Bushing.

9. Install the new return spring onto the new choke
shaft, so the upper leg of the spring is between
the two formed “stops” on the end of the choke
shaft. See Figure 5-63.

11. Place a drop of Loctite® on the threads of each
new screw. Position and install the new choke
plate to the flat side of the choke shaft. Start the
two screws. Close the choke and check the plate
alignment within the carburetor throat, then
tighten the screws securely. Do not overtighten.
See Figure 5-64.

Figure 5-64. Installing Choke Plate.

12. Check for proper operation and free movement of
the parts. Install the new cap.

NOTE: Make sure it stays in this location during

the following step.

Figure 5-63. Choke Shaft and Spring Details.

10. Slide the choke shaft and spring into the
carburetor. Pivot (preload) the shaft and set the
inner leg of the spring, against the formed stop
within the choke lever as originally assembled.
See Figure 5-60. The opposing leg of the spring
must still be between the formed “stops” of the
choke shaft.

Always use new gaskets when servicing or reinstalling
carburetors. Repair kits are available which include
new gaskets and other components. Service/repair kits
available for Keihin BK two-barrel carburetors and
affiliated components are:

Carburetor Overhaul Kit
Float Kit
Fuel Solenoid Kit
Choke Repair Kit
Bowl Kit
High Altitude Kit (1525-3048 m/5,000-10,000 ft.)
High Altitude Kit (Over 3048 m/10,000 ft.)

5.28

Section 5

Fuel System and Governor

26

32

27

31

22

24

28

4
5
6

2

3

30

29

23

25

7

9

1

21
20

17

18

19

1. Carburetor Body Subassembly

2. Idle Speed Screw

3. Idle Speed Spring

8

4. Screw

9

5. Ground Lead

6. Retaining Washer

7. Slow Jet - RH Side

8. Slow Jet - LH Side

9. O-Ring (Slow Jet) (2)

10. Fuel Bowl

11. O-Ring (Fuel Bowl - Upper)

12. O-Ring (Fuel Bowl - Lower)

13. Drain Screw

14. Bowl Screw (4)

15. Fuel Solenoid

16. Sealing Washer

17. Float

18. Pin

19. Screw

20. Float Clip

21. Float Valve/Inlet Needle

22. Main Nozzle - Right Side

23. Main Nozzle - Left Side

24. Main Jet - Right Side

25. Main Jet - Left Side

26. Choke Dust Cap

27. Choke Shaft

28. Spring

29. Bushing

30. Choke Lever

31. Choke Plate

32. Choke Plate Screw (2)

5

11

12

13

16

Figure 5-65. Keihin BK T wo-Barrel Carburetor - Exploded View.

10

14

15

5.29

Section 5
Fuel System and Governor

Governor

General

The engine is equipped with a centrifugal flyweight
mechanical governor. It is designed to hold the engine
speed constant under changing load conditions. The
governor gear/flyweight mechanism is mounted
inside the crankcase on the oil pan, and is driven off
the gear on the camshaft. The governor works as
follows:

• Centrifugal force acting on the rotating governor
gear assembly causes the flyweights to move
outward as speed increases. Governor spring
tension moves them inward as speed decreases.

• As the flyweights move outward, they cause the
regulating pin to move outward.

• The regulating pin contacts the tab on the cross
shaft causing the shaft to rotate. One end of the
cross shaft protrudes through the crankcase. The
rotating action of the cross shaft is transmitted to
the throttle lever of the carburetor through the
external linkage. See Figure 5-66.

• When the engine is at rest, and the throttle is in
the “fast” position, the tension of the governor
spring holds the throttle plate open. When the
engine is operating, the governor gear assembly
is rotating. The force applied by the regulating
pin against the cross shaft tends to close the
throttle plate. The governor spring tension and
the force applied by the regulating pin balance
each other during operation, to maintain engine
speed.

• When load is applied and the engine speed and
governor gear speed decreases, the governor
spring tension moves the governor lever to open
the throttle plate wider. This allows more fuel
into the engine, increasing engine speed. As
speed reaches the governed setting, the governor
spring tension and the force applied by the
regulating pin will again offset each other to hold
a steady engine speed.

Adjustments

General

The governed speed setting is determined by the
position of the throttle control. It can be variable or
constant, depending on the engine application.

Hex
Nut

Cross Shaft

Governor
Arm

Governor Spring

Figure 5-66. Governor Controls and Linkage
(External).

Initial Adjustment

NOTE: EFI engines require a special initial

adjustment procedure, which is covered in
subsection 5B. Refer to “Initial Governor
Adjustment” in that section for setting the
governor on EFI-equipped engines.

Procedure - Carburetor Equipped Engines

Make this adjustment whenever the governor arm is
loosened or removed from the cross shaft. See Figure
5-66 and adjust as follows:

1. Make sure the throttle linkage is connected to the
governor lever and the throttle lever on the
carburetor.

2. Loosen the hex nut holding the governor lever to
the cross shaft.

3. Move the governor lever toward the carburetor
as far as it will move (wide-open throttle) and
hold in position.

5.30

4. Insert a nail into the hole in the end of the cross
shaft and rotate the shaft counterclockwise as far
as it will turn, then tighten the hex nut securely.

Section 5

Fuel System and Governor

Sensitivity Adjustment

Governor sensitivity is adjusted by repositioning the
governor spring in the holes of the governor lever. If
speed surging occurs with a change in engine load, the
governor is set too sensitive. If a big drop in speed
occurs when normal load is applied, the governor
should be set for greater sensitivity. See Figure 5-66
and adjust as follows:

1. To increase the sensitivity, move the spring closer
to the governor lever pivot point.

2. To decrease the sensitivity, move the spring away
from the governor lever pivot point.

High Speed (RPM) Adjustment (Refer to Figures
5-67, 5-68, or 5-69.)

Left Side Pull

1. With the engine running, move the throttle

control to fast. Use a tachometer to check the
RPM speed.

2. Loosen the lock nut on the high speed adjusting
screw. Turn the screw counterclockwise to
decrease, or clockwise to increase RPM speed.
Check RPM with a tachometer.

3. When the desired RPM speed is obtained,
retighten the lock nut.

NOTE: When the throttle and choke control cables

are routed side-by-side, especially under a
single clamp, there must be a small gap
between the cables to prevent internal
binding. After the high-speed setting has
been completed, check that there is a gap of
at least 0.5 mm (0.020 in.) between the control
cables.

Throttle Control
Lever #2

5

Choke
Control
Cable

Throttle
Control
Cable

Kill Switch
Adjusting Screw

Dual Control High
Speed Lever Stop
Screw "Do Not
Remove"

Figure 5-67. Governor Control Connections.

Kill Switch

High Speed
Adjusting
Screw

Choke Control
Lever #1

High Speed
Control Lever

Choke Linkage

Z Bend

Throttle
Control Cable

Choke
Control
Cable

Right Side Pull

5.31

Section 5
Fuel System and Governor

Choke Lever Detail

Choke Cable

Control
Bracket

Blower Housing

Washer

Spring

Fastener

Choke Lever

(See Detail at Left)

Screw and Nut

Control Lever

Lock Nut

Fastener

Clamp

Washer

Throttle
Cable

Fuel
Pump

Choke Lever

Lock
Nut

Linkage

Screw

Spring
Washer

Spacer

Bushing

Clamp

Clip

Lever

Spring

Washer

Locker Nut

Throttle Lever

Bushing

Fuel Line

Spring
Linkage
Bushing
Throttle Shaft

Spacer

Bracket

Deflector

(If So Equipped)
(Place Between Valley
Baffle and Throttle
Shaft Bracket)

Figure 5-68. Governor Used with Commercial Mower Air Cleaner (CV17-745).

Commercial Mower Governor
Arrangement

The Commercial Mower governor arrangement shown
in Figure 5-68 is used primarily on wide area walk
behind mower applications. The initial adjustment
and sensitivity adjustment is the same as for the
standard governor. The governor and controls for the
CV750 engine is shown in Figure 5-69. Should the
governor spring be disconnected from the throttle
lever and governor lever, reconnect it as follows:

1. Hook the long end of the spring through the hole
in the lever from the left side.

2. Rotate the spring 180° until hooked as shown in
Figure 5-69.

3. Hook the short end of the spring into the
appropriate hole in the governor lever. Refer to
the appropriate chart in Section 11 - "Reassembly"
of this manual for the correct hole to use for the
speed involved.

5.32

Screw

Section 5

Fuel System and Governor

Washer

Lock Nut

Spring
Washer

Spacer

Bushing

Choke Linkage

Clamp
and Screw

Control
Bracket

Choke
Cable

Screw

Spring

Washer

Hex Nut Screw

Throttle Control Lever

Lock Nut

Throttle Linkage

Bushing

5

Throttle
Cable

Fuel Pump

Linkage Spring

Governor Lever

Governor Spring

Figure 5-69. Governor/Controls Assembly (CV750).

Washer

Spacer

Lock Nut

Throttle Shaft

Bushing

Throttle Shaft Bracket

Throttle Lever

Clamp

Fuel

Deflector (If
So Equipped)

5.33

Section 5B

EFI Fuel System

Section 5B

Electronic Fuel Injection (EFI)

Fuel System

Contents Page(s)

Description

Initial Starting/Priming Procedure .........................................................................................................................5B.2

Fuel Recommendations................................................................................................................................... 5B.2-5B.3

EFI Fuel System Components .................................................................................................................................5B.3

Operation ...................................................................................................................................................................5B.3

Important Service Notes ..........................................................................................................................................5B.4

Electrical Components

Electronic Control Unit (ECU) .......................................................................................................................5B.4-5B.5

Engine Speed Sensor ....................................................................................................................................... 5B.5-5B.6

Throttle Position Sensor (TPS) and Initialization Procedures ...................................................................5B.6-5B.9

Engine (Oil) Temperature Sensor ................................................................................................................5B.9-5B.10

Oxygen Sensor.............................................................................................................................................. 5B.10-5B.12

Electrical Relay ............................................................................................................................................. 5B.12-5B.13

Fuel Injectors ................................................................................................................................................ 5B.13-5B.16

Ignition System .......................................................................................................................................................5B.17

Spark Plugs ..............................................................................................................................................................5B.18

Wiring Harness ....................................................................................................................................................... 5B.18

Battery Charging System ....................................................................................................................................... 5B.18

5B

Fuel Components

Fuel Pump .....................................................................................................................................................5B.18-5B.19

Fuel Pressure Regulator ..............................................................................................................................5B.19-5B.21

Fuel Filter .................................................................................................................................................................5B.21

Fuel Rail ...................................................................................................................................................................5B.21

Fuel Line........................................................................................................................................................ 5B.21-5B.22

Throttle Body/Intake Manifold Assembly ..........................................................................................................5B.22

Idle Speed Adjustment (RPM) ...................................................................................................................5B.22-5B.23

Initial Governor Adjustment ......................................................................................................................5B.23-5B.25

Troubleshooting

Troubleshooting Guide ..........................................................................................................................................5B.25

Electrical System ..........................................................................................................................................5B.25-5B.29

Fuel System ..............................................................................................................................................................5B.30

Fault Codes ...................................................................................................................................................5B.30-5B.38

Troubleshooting Flow Chart ......................................................................................................................5B.38-5B.39

Flow Chart Diagnostic Aids .......................................................................................................................5B.40-5B.41

EFI Service Tools ............................................................................................................................... Refer to Section 2

5B.1

Section 5B
EFI Fuel System

Description

WARNING

Explosive Fuel can cause fires and
severe burns.

Fuel system ALWAYS remains under
HIGH PRESSURE.

WARNING: Explosive Fuel!

Gasoline is extremely flammable and its vapors can explode
if ignited. Store gasoline only in approved containers, in
well ventilated, unoccupied buildings, away from sparks or
flames. Do not fill the fuel tank while the engine is hot or
running, since spilled fuel could ignite if it comes in contact
with hot parts or sparks from ignition. Do not start the
engine near spilled fuel. Never use gasoline as a cleaning
agent.

The EFI fuel system remains under high pressure even
when the engine is stopped. Before attempting to service
any part of the fuel system, the pressure must be relieved.
Pressure tester, (part of EFI Service Kit, see Section 2) has
an integral relief valve. Connect the black tester hose to the
test valve in the fuel rail. Route the clear hose into a
portable gasoline container. Depress the button on the tester
relief valve.

Initial Starting/Priming Procedure

Important: The EFI fuel system must be purged of air
(primed) prior to the initial start up, and/or any time
the system has been disassembled or the fuel tank run
dry.

2. For plastic-cased ECU’s below 24 584 28-S, the
system can be primed by manually cycling the
fuel pump.

a. Turn the key switch to the “on/run” position.

The fuel pump will run for about three
seconds and stop. Turn the switch off and
back on to restart the fuel pump. Repeat
this procedure until the fuel pump has
cycled five times, then start the engine.

3. The system can also be primed similar to
relieving pressure.

a. Connect the pressure gauge as described

above for relieving fuel pressure. Depress
and hold the release button and crank the
engine until the air is purged and fuel is
visible in the discharge tube. If fuel is not
visible after 10 seconds, stop cranking and
allow the starter to cool for 60 seconds.

Fuel Recommendations

General Recommendations

Purchase gasoline in small quantities and store in
clean, approved containers. An approved container
with a capacity of 2 gallons or less with a pouring
spout is recommended. Such a container is easier to
handle and helps prevent spillage during refueling.

• Do not use gasoline left over from the previous
season, to minimize gum deposits in your fuel
system, and to ensure easy starting.

• Do not add oil to the gasoline.

• Do not overfill the fuel tank. Leave room for the
fuel to expand.

1. Locate the electronic control unit (ECU) for the
EFI system. Check the part number on the end. If
the Part No. is 24 584 28 or higher, the ECU has a
built-in priming feature.

a. Turn the key switch to the “on/run” position.

You will hear the fuel pump cycle on and off.
When the fuel pump stops cycling
(approximately one minute), the system is
primed; start the engine.

5B.2

Fuel Type

Do not use leaded gasoline, as component damage
will result. Any costs/damages incurred as a result of
using leaded fuel will not be warranted. Use only
clean, fresh, unleaded gasoline with a pump sticker
octane rating of 87 or higher. In countries using the
Research method, it should be 90 octane minimum.

Section 5B

EFI Fuel System

Gasoline/Alcohol blends

Gasohol (up to 10% ethyl alcohol, 90% unleaded
gasoline by volume) is approved as a fuel for Kohler
EFI engines. Other gasoline/alcohol blends are not
approved.

Gasoline/Ether blends

Methyl Tertiary Butyl Ether (MTBE) and unleaded
gasoline blends (up to a maximum of 15% MTBE by
volume) are approved as a fuel for Kohler EFI engines.
Other gasoline/ether blends are not approved.

EFI Fuel System Components

General

The Electronic Fuel Injection (EFI) system is a
complete engine fuel and ignition management
design. The system includes the following principal
components:

• Fuel Pump

• Fuel Filter

• Fuel Rail

• Fuel Line(s)

• Fuel Pressure Regulator

• Fuel Injectors

• Throttle Body/Intake Manifold

• Engine Control Unit (ECU)

• Ignition Coils

• Engine (Oil) Temperature Sensor

• Throttle Position Sensor (TPS)

• Speed Sensor

• Oxygen Sensor

• Wire Harness Assembly & Affiliated Wiring,

• Malfunction Indicator Light (MIL)

An electric fuel pump is used to move fuel from the
tank through the fuel line and in-line fuel filter. A fuel
pressure regulator maintains a system operating
pressure of 39 psi and returns any excess fuel to the
tank. At the engine, fuel is fed through the fuel rail
and into the injectors, which inject it into the intake
ports. The ECU controls the amount of fuel by varying
the length of time that the injectors are “on.” This can
range from 1.5-8.0 milliseconds depending on fuel
requirements. The controlled injection of the fuel
occurs each crankshaft revolution, or twice for each 4­stroke cycle. One-half the total amount of fuel needed
for one firing of a cylinder is injected during each
injection. When the intake valve opens, the fuel/air
mixture is drawn into the combustion chamber,
ignited, and burned.

The ECU controls the amount of fuel being injected
and the ignition timing by monitoring the primary
sensor signals for engine temperature, speed (RPM),
and throttle position (load). These primary signals are
compared to preprogrammed “maps” in the ECU
computer chip, and the ECU adjusts the fuel delivery
to match the mapped values. After the engine reached
operating temperature, an exhaust gas oxygen sensor
provides feedback to the ECU based upon the amount
of unused oxygen in the exhaust, indicating whether
the fuel mixture being delivered is rich or lean. Based
upon this feedback, the ECU further adjusts fuel input
to re-establish the ideal air/fuel ratio. This operating
mode is referred to as “closed loop” operation. The
EFI system operates “closed loop” when all three of
the following conditions are met:

a. The oil temperature is greater than 35°C (86°F).

5B

Operation

The EFI system is designed to provide peak engine
performance with optimum fuel efficiency and lowest
possible emissions. The ignition and injection
functions are electronically controlled, monitored and
continually corrected during operation to maintain the
theoretical ideal or “stoichiometric” air/fuel ratio of

14.7:1.

The central component of the system is the Motronic
Engine Control Unit (ECU) which manages system
operation, determining the best combination of fuel
mixture and ignition timing for the current operating
conditions.

b. The oxygen sensor has warmed sufficiently to

provide a signal (minimum 375°C, 709°F).

c. Engine operation is at a steady state (not starting,

warming up, accelerating, etc.).

During “closed loop” operation the ECU has the
ability to readjust temporary and learned adaptive
controls, providing compensation for changes in
overall engine condition and operating environment,

™

so it will be able to maintain the ideal air/fuel ratio of

14.7:1. The system requires a minimum engine oil
temperature greater than 55°C (130°F) to properly
adapt. These adaptive values are maintained as long
as the ECU is “powered up” by the battery.

5B.3

Section 5B
EFI Fuel System

During certain operating periods such as cold starts,
warm up, acceleration, etc., an air/fuel ratio richer
than 14.7:1 is required and the system operates in an
“open loop” mode. In “open loop” operation the
oxygen sensor output is not used, and the controlling
adjustments are based on the primary sensor signals
and programmed maps only. The system operates
“open loop” whenever the three conditions for closed
loop operation (above) are not being met.

Important Service Notes!

• Cleanliness is essential and must be maintained
at all times when servicing or working on the EFI
system. Dirt, even in small quantities, can cause
significant problems.

• Clean any joint or fitting with parts cleaning
solvent before opening to prevent dirt from
entering the system.

• Always depressurize the fuel system through the
test valve in the fuel rail before disconnecting or
servicing any fuel system components. See fuel
warning on page 5B.2.

• Never use a quick battery charger to start the
engine.

• Do not charge the battery with the key switch
‘‘on.’’

• Always disconnect the negative (-) battery cable
before charging the battery, and also unplug the
harness from the ECU before performing any
welding on the equipment.

Electrical Components

Electronic Control Unit (ECU)

• Never attempt to service any fuel system
component while the engine is running or the
ignition switch is "on".

• Do not use compressed air if the system is open.
Cover any parts removed and wrap any open
joints with plastic if they will remain open for
any length of time. New parts should be removed
from their protective packaging just prior to
installation.

• Avoid direct water or spray contact with system
components.

• Do not disconnect or reconnect the main ECU
wiring harness connector or any individual
components with the ignition ‘‘on.’’ This can send
a damaging voltage spike through the ECU.

• Do not allow the battery cables to touch opposing
terminals. When connecting battery cables attach
the positive (+) cable to the positive (+) battery
terminal first, followed by the negative (-) cable to
the negative (-) battery terminal.

Figure 5B-1. “24 Pin” (MSE 1.0) Plastic-Cased ECU.

Figure 5B-2. “32 Pin” (MSE 1.1) Plastic-Cased ECU.

• Never start the engine when the cables are loose
or poorly connected to the battery terminals.

• Never disconnect the battery while the engine is
running.

5B.4

Section 5B

EFI Fuel System

Two different ECU styles have been used in CV EFI
production. Each has a plastic case, but they differ in
having a 24 pin or 32 pin connector block, and are
identified as MSE 1.0 or MSE 1.1 respectively. See
Figures 5B-1 and 5B-2. Basic function and operating
control remains the same between the two, however
due to differences in the internal circuitry as well as
the wiring harness, the ECU’s are not interchangeable.
Certain service/troubleshooting procedures will also
differ, so where applicable, they are covered
individually as: “24 Pin” (MSE 1.0) Plastic-Cased
ECU, or “32 Pin” (MSE 1.1) Plastic-Cased ECU.

General

The ECU is the brain or central processing computer
of the entire EFI system. During operation, sensors
continuously gather data which is relayed through the
wiring harness to input circuits within the ECU.
Signals to the ECU include: ignition (on/off),
crankshaft position and speed (RPM), throttle
position, oil temperature, exhaust oxygen levels, and
battery voltage. The ECU compares the input signals
to the programmed maps in its memory to determine
the appropriate fuel and spark requirements for the
immediate operating conditions. The ECU then sends
output signals to set the injector duration and ignition
timing.

To prevent engine over-speed and possible failure, a
“rev-limiting” feature is programmed into the ECU. If
the maximum RPM limit (4500) is exceeded, the ECU
suppresses the injection signals, cutting off the fuel
flow. This process repeats itself in rapid succession,
limiting operation to the preset maximum.

Service

Never attempt to disassemble the ECU. It is sealed to
prevent damage to internal components. Warranty is
void if the case is opened or tampered with in any
way.

All operating and control functions within the ECU
are preset. No internal servicing or readjustment may
be performed. If a problem is encountered, and you
determine the ECU to be faulty, contact your source of
supply. Do not replace the ECU without factory
authorization.

The relationship between the ECU and the throttle
position sensor (TPS) is very critical to proper system
operation. If the TPS or ECU is changed, or the
mounting position of the TPS is altered, the
appropriate “TPS Initialization Procedure” (see pages
5B.8 and 5B.9) must be performed to restore the
synchronization.

5B

The ECU continually performs a diagnostic check of
itself, each of the sensors, and the system
performance. If a fault is detected, the ECU turns on
the Malfunction Indicator Light (MIL) on the
equipment control panel, stores the fault code in its
fault memory, and goes into a default operating mode.
Depending on the significance or severity of the fault,
normal operation may continue, or “limp home”
operation (slowed speed, richer running) may be
initiated. A technician can access the stored fault code
using a “blink code” diagnosis flashed out through the
MIL. An optional computer software diagnostic
program is also available, see Section 2.

The ECU requires a minimum of 7.0 volts to operate.
The adaptive memory in the ECU is operational
whenever the required voltage is present, however the
adapted values are lost if the power supply is
disrupted for any reason. The ECU will “relearn” the
adapted values if the engine is operated for 10-15
minutes at varying speeds and loads after the oil
temperature exceeds 55°C (130°F).

Engine Speed Sensor

Figure 5B-3. Engine Speed Sensor.

5B.5

Section 5B
EFI Fuel System

General

The engine speed sensor is essential to engine
operation; constantly monitoring the rotational speed
(RPM) of the crankshaft. A ferromagnetic 60-tooth ring
gear with two consecutive teeth missing is mounted
on the flywheel. The inductive speed sensor is
mounted 1.5 ± 0.25 mm (0.059 ± 0.010 in.) away from
the ring gear. During rotation, an AC voltage pulse is
created within the sensor for each passing tooth. The
ECU calculates engine speed from the time interval
between the consecutive pulses. The two-tooth gap
creates an interrupted input signal, corresponding to
specific crankshaft position (84° BTDC) for cylinder
#1. This signal serves as a reference for the control of
ignition timing by the ECU. Synchronization of the
inductive speed pickup and crankshaft position takes
place during the first two revolutions each time the
engine is started. The sensor must be properly
connected at all times. If the sensor becomes
disconnected for any reason, the engine will quit
running.

Service

The engine speed sensor is a sealed, non-serviceable
assembly. If “Fault Code” diagnosis indicates a
problem within this area, test and correct as follows.

Dual Aligning Rails

Corresponds
T o #10 Pin
T erminal In Main
Connector

Test T erminals

Figure 5B-4. Speed Sensor Connector .

7. a. If the resistance is incorrect, remove the screw
securing the sensor to the mounting
bracket and replace the sensor.

b. If the resistance in step 5 was incorrect, but

the resistance of the sensor alone was correct,
test the main harness circuits between the
sensor connector terminals and the
corresponding pin terminals (#9 and #10) in
the main connector. Correct any observed
problem, reconnect the sensor, and perform
step 5 again.

Corresponds T o
#9 Pin T erminal In
Main Connector

1. Check the mounting and air gap of the sensor. It

must be 1.5 mm ± 0.25 mm (0.059 ± 0.010 in.).

2. Inspect the wiring and connections for damage or
problems.

3. Make sure the engine has resistor type spark
plugs.

4. Disconnect the main harness connector from the
ECU.

5. Connect an ohmmeter between the #9 and #10 pin
terminals.

See chart on page 5B.26 or 5B.29, according to
ECU style. A resistance value of 750-1000
room temperature (20°C, 68°F) should be
obtained. If resistance is correct, check the
mounting, air gap, toothed ring gear (damage,
run-out, etc.), and flywheel key.

6. Disconnect the speed sensor connector from the
wiring harness. It is the connector with one heavy
black lead (see Figure 5B-4). Viewing the
connector as shown (dual aligning rails on top),
test resistance between the terminals indicated. A
reading of 750-1000

Ω Ω

Ω should again be obtained.

Ω Ω

ΩΩ

Ω at

ΩΩ

Throttle Position Sensor (TPS)

2

1

1. Throttle V alve Shaft

2. Resistor Track

3. Wiper Arm With Wiper

4. Electrical Connection

Figure 5B-5. Throttle Position Sensor Details.

3

4

5B.6

Section 5B

EFI Fuel System

General

The throttle position sensor (TPS) is used to indicate
throttle plate angle to the ECU. Since the throttle (by
way of the governor) reacts to engine load, the angle
of the throttle plate is directly related to the load on
the engine.

Figure 5B-6. TPS Location.

Mounted on the throttle body/intake manifold and
operated directly off the end of the throttle shaft, the
TPS works like a rheostat, varying the voltage signal
to the ECU in direct correlation to the angle of the
throttle plate. This signal, along with the other sensor
signals, is processed by the ECU and compared to the
internal pre-programmed maps to determine the
required fuel and ignition settings for the amount of
load.

The correct position of the TPS is established and set
at the factory. Do not loosen the TPS or alter the
mounting position unless absolutely required by fault
code diagnosis or throttle shaft service. If the TPS is
loosened or repositioned, the appropriate “TPS
Initialization Procedure must be performed to
reestablish the baseline relationship between the ECU
and the TPS.

Service

The TPS is a sealed, non-serviceable assembly. If
diagnosis indicates a bad sensor, complete
replacement is necessary. If a blink code indicates a
problem with the TPS, it can be tested as follows:

3. a. Use an ohmmeter and connect the ohmmeter
leads as follows to test: (See chart on page
5B.26 or 5B.29.).

“24 Pin” (MSE 1.0) Plastic-Cased ECU: Red
(positive) ohmmeter lead to #8 pin terminal, and
Black (negative) ohmmeter lead to #4 pin
terminal.

“32 Pin” (MSE 1.1) Plastic-Cased ECU: Red
(positive) ohmmeter lead to #8 pin terminal, and
Black (negative) ohmmeter lead to #4 pin
terminal.

b. Hold the throttle closed and check the

resistance. It should be 800-1200

4. Leave the leads connected to the pin terminals as

described in step 3. Rotate the throttle shaft
slowly counterclockwise to the full throttle
position. Monitor the dial during rotation for
indication of any momentary short or open
circuits. Note the resistance at the full throttle
position. It should be 1800-3000

5. Disconnect the main wiring harness connector

from the TPS, leaving the TPS assembled to the
manifold. Refer to the chart below and perform
the resistance checks indicated between the
terminals in the TPS switch, with the throttle in
the positions specified.

Throttle

Position

Closed

Closed

Full
Full
Any

If the resistance values in steps 3, 4, and 5 are
within specifications, go to step 6.

If the resistance values are not within
specifications, or a momentary short or open
circuit was detected during rotation (step 4), the
TPS needs to be replaced, go to step 7.

Between

Terminals

2 & 3
1 & 3
2 & 3
1 & 3
1 & 2

Resistance

Value (Ω)

800-1200
1800-3000
1800-3000

800-1200
1600-2500

ΩΩ

Ω.

ΩΩ

ΩΩ

Ω.

ΩΩ

Continuity

Yes
Yes
Yes
Yes
Yes

5B

1. Counting the number of turns, back out the idle
speed adjusting screw (counterclockwise) until
the throttle plates can be closed completely.

2. Disconnect the main harness connector from the
ECU, but leave the TPS mounted to the throttle
body/manifold.

6. Check the TPS circuits (input, ground) between
the TPS plug and the main harness connector for
continuity, damage, etc. See chart on page 5B-26
or 5B-29.

5B.7

Section 5B
EFI Fuel System

“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin
circuits #8 and #4.

“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin
circuits #8 and #4.

a. Repair or replace as required.

b. Turn the idle speed screw back in to its

original setting.

c. Reconnect connector plugs, start engine and

retest system operation.

7. Remove the two mounting screws from the TPS.
Save the screws for reuse. Remove and discard
the faulty TPS. Install the replacement TPS and
secure with the original mounting screws.

a. Reconnect both connector plugs.

b. Perform the appropriate “TPS Initialization

Procedure” integrating the new sensor to the
ECU.

TPS Initialization Procedure

For “24 Pin” (MSE 1.0) Plastic-Cased ECU only

1. Check that the basic engine, all sensors, fuel, fuel
pressure, and battery are good and functionally
within specifications.

Important!

2. Remove/disconnect all external loads from the
engine (belts, pumps, electric PTO clutch,
alternator, rectifier-regulator, etc.).

3. Start the engine and allow it to warm up for 5-10
minutes, so oil temperature is above 55°C (130°F).

4. Move the throttle control to the idle position and
allow the engine to stabilize for a minimum of
one minute.

5. Install a heavy rubber band around the throttle
lever and the manifold boss. On some EFI engines
there is a dampening spring on the end of the idle
speed screw. The dampening spring (if used)
should be fully compressed and the tab on the
throttle lever in direct contact with the speed
screw. Adjust the idle speed to 1500 RPM, using a
tachometer.

6. Shut off the engine.

7. Locate the service connector plug in the wiring
harness. Connect a jumper wire from the TPS
initialization pin #24 (violet wire) to the battery
voltage pin (red wire), or use the jumper
connector plug with the blue jumper wire. See
Figure 5B-7.

Figure 5B-7. Service Connector Plug, Plastic
Cased ECU Harness.

8. Hold the throttle against the idle speed stop
screw, turn the ignition switch to the “on”
position (do not start the engine), and observe the
Malfunction Indicator Light (MIL).

a. The light should blink on/off quickly for

approximately 3 seconds and then go off and
stay off, indicating the initialization
procedure has been successful.

b. If the light stays on or blinking ceases

prematurely, the procedure was unsuccessful
and must be repeated. Possible causes for
unsuccessful learning may be: 1) Movement
occurred in either the TPS or throttle shaft
during procedure, 2) Crankshaft movement
wasdetected by the speed sensor during
procedure, 3) Throttle plate position was out
of learnable range (recheck the 1500 RPM idle
speed adjustment), or 4) Problem with ECU
or TPS.

9. When the initialization procedure has been
successfully completed, turn off the key switch,
remove the jumper wire or connector, and
remove the rubber band from the throttle lever.

10. Disconnect the ECU connector plug or the
negative (-) battery cable temporarily (one
minute minimum) to clear all learned
adjustments.

5B.8

Section 5B

EFI Fuel System

11. Reconnect the battery cable and all external loads.
Remove the rubber band from the throttle lever.
Readjust the idle speed to the equipment
manufacturer’s specified setting and recheck the
high-speed, no-load RPM setting. Observe the
overall performance.

TPS Initialization Procedure

For “32 Pin” (MSE 1.1) Plastic-Cased ECU Only

(“Auto-Learn” Initialization)

1. Check that the basic engine, all sensors, fuel, fuel
pressure, and battery are good and functionally
within specifications.

Important!

2. Remove/disconnect all external loads from the
engine (belts, pumps, electric PTO clutch,
alternator, rectifier-regulator, etc.).

3. Locate the service connector plug in the wiring
harness. To initiate the TPS auto-learn function,
connect a jumper wire from the TPS initialization
pin #24 (violet wire) to the battery voltage pin
(red wire), or use the jumper plug with the blue
jumper wire. If using the PC-based diagnostic
software (see Section 2), go to “Special Tests” and
follow the prompts to complete.

9. Shut off the engine. If the learn procedure was
successfully completed, the external loads
removed/disconnected in Step 2 may be
reconnected.

If the procedure was unsuccessful see Steps a.
and b. following.

a. If the “MIL” goes back to blinking 4

consecutive blinks every 2 seconds during the
procedure, the engine and O2 sensor have
cooled down and gone out of “closed-loop”
operation, prohibiting the learning from
occurring. Repeat Steps 6-9.

b. If the “MIL” stays “on” continuously for more

than 15 seconds during the procedure, there is
probably a fault code present, turn off the
ignition. Then initiate the fault code sequence,
by turning the key switch on-off-on-off-on,
leaving the key “on” in the last sequence (each
key on/off sequence must be less than 2.5
seconds long). The fault detected must be
corrected before the “auto-learn” function can
be re-initiated. The PC-based diagnostic
software may be used to read out the fault
code and assist with troubleshooting and
repair.

5B

4. Start the engine and immediately observe the
Malfunction Indicator Light (MIL). The light
should start blinking 4 consecutive times every 2
seconds.

5. Remove the jumper wire or plug from the service
connector plug.

6. Run the engine at full throttle (above 3000 RPM),
to warm up the engine and initiate O
function in “closed-loop” operation.

7. Watch the “MIL”. When the light starts blinking
rapidly, (5 blinks per second), move the throttle
lever to the low idle speed position. Check and
adjust the idle speed to 1500 RPM, using a
tachometer. The lamp should continue to blink
rapidly for another 30 seconds before switching
to a slow blink.

8. When the “MIL” blinks slowly, do not do
anything but wait until the “MIL” shuts off. This
indicates that this procedure has been completed
successfully.

sensor

2

Engine (Oil) Temperature Sensor

Figure 5B-8. Engine (Oil) T emperature Sensor.

5B.9

Section 5B
EFI Fuel System

General

The engine (oil) temperature sensor (Figure 5B-8) is
used by the system to help determine fuel
requirements for starting (a cold engine needs more
fuel than one at or near operating temperature).
Mounted in the oil filter adapter housing, it has a
temperature-sensitive resistor that extends into the oil
flow. The resistance changes with oil temperature,
altering the voltage sent to the ECU. Using a table
stored in its memory, the ECU correlates the voltage
drop to a specific temperature. Using the fuel delivery
“maps”, the ECU then knows how much fuel is
required for starting at that temperature.

Service

The temperature sensor is a sealed, non-serviceable
assembly. A faulty sensor must be replaced. If a blink
code indicates a problem with the temperature sensor,
it can be tested as follows:

1. Remove the temperature sensor from the adapter
housing and cap or block the adapter hole.

2. Wipe the sensor clean and allow it to reach room
temperature (20°C, 68°F).

3. Unplug the main harness connector from the
ECU.

4. With the sensor still connected, check the
temperature sensor circuit resistance between the
#6 and #4 pin terminals (see chart on page 5B.26
(24 pin) or 5B.29 (32 pin) for pin positions). The
value should be 2375-2625

5. Unplug the sensor from the wire harness and
check the sensor resistance separately. Resistance
value should again be 2375-2625

ΩΩ

Ω.

ΩΩ

ΩΩ

Ω.

ΩΩ

Oxygen Sensor

Figure 5B-9. Oxygen Sensor.

General

The oxygen sensor functions like a small battery,
generating a voltage signal to the ECU based upon the
difference in oxygen content between the exhaust gas
and the ambient air.

The tip of the sensor, protruding into the exhaust gas,
is hollow (see cutaway Figure 5B-10). The outer
portion of the tip is surrounded by the exhaust gas,
with the inner portion exposed to the ambient air.
When the oxygen concentration on one side of the tip
is different than that of the other side, a voltage signal
between 0.2 and 1.0 volts is generated between the
electrodes and sent to the ECU. The voltage signal
tells the ECU if the engine is straying from the ideal

14.7:1 fuel mixture, and the ECU then adjusts the
injector pulse accordingly.

4

1

3

2

5

6

8

7

a. If the resistance is out of specifications,

replace the temperature sensor.

b. If it is within specifications, proceed to Step 6.

6. Check the circuits (input, ground), from the main
harness connector to the sensor plug for
continuity, damage, etc. Connect one ohmmeter
lead to pin terminal #6 in the main harness
connector (as in step 4). Connect the other lead to
terminal #1 in the sensor plug (see diagram).
Continuity should be indicated. Repeat the test
between pin terminal #4 and terminal #2 in the
sensor plug.

5B.10

1. Connection Cable

2. Disc Spring

3. Ceramic Support Tube

4. Protective Sleeve

Figure 5B-10. Cutaway of Oxygen Sensor .

5. Contact Element

6. Sensor Housing

7. Active Ceramic Sensor

8. Protective Tube

Section 5B

EFI Fuel System

The oxygen sensor can function only after being
heated by exhaust temperatures to a minimum of
375°C (709°F). A cold oxygen sensor will require
approximately 1-2 minutes at moderate engine load to
warm sufficiently to generate a voltage signal. Proper
grounding is also critical. The oxygen sensor grounds
through the metal shell, so a good, solid, unbroken
ground path back through the exhaust system
components, engine, and wiring harness is required.
Any disruption or break in the ground circuit can
affect the output signal and trigger misleading fault
codes. Keep that in mind when doing any
troubleshooting associated with the oxygen sensor.
The oxygen sensor can also be contaminated by leaded
fuel, certain RTV and/or other silicone compounds,
carburetor cleaners, etc. Use only those products
indicated as “O

Service

Like the other sensors already discussed, the oxygen
sensor is a non-serviceable component. Complete
replacement is required if it is faulty. The sensor and
wiring harness can be checked as follows.

NOTE: All tests should be conducted with a good

quality, high-impedance, digital VOA meter
for accurate results.

1. Oxygen sensor must be hot (minimum of 400°C,
752°F). Run engine for about 5 minutes. With the
engine running, disconnect the oxygen sensor
lead from the wiring harness. Set VOA meter for
DC volts and connect the red lead to the
disconnected sensor lead, and the black lead to
the sensor shell. Look for a voltage reading from

0.2 v-1.0 v.

a. If voltage is in the specified range, go to Step

2.

b. If voltage is not in the specified range,

reconnect the oxygen sensor lead. With the
lead connected, probe or connect the sensor
connection with the red VOA meter lead.
Attach the black VOA meter lead to a good
ground location. Start and run the engine at
3/4 throttle and note the voltage reading being
signaled by the oxygen sensor. The reading
should cycle between 0.2 v and 1.0 v, which
indicates the oxygen sensor is functioning
normally and fuel delivery is within
prescribed parameters. If the voltage readings
show a steady decline, rev the engine and
check the indicated reading again. If the
voltage momentarily increases and then again

Sensor Safe.”

2

declines, without cycling, the engine may be
running lean due to incorrect TPS initialization.
Shut off the engine, perform TPS initialization,
and then repeat the test. If TPS initialization
cannot be achieved, perform step c.

c. Replace the oxygen sensor (see next page).

Run the engine long enough to bring the new
sensor up to temperature and repeat the
output test from step 1. The cycling voltage
from 0.2 to 1.0 v should be indicated.

2. Move the black voltmeter lead to the engine

ground location and repeat the output test. The
same voltage (0.2 v-1.0 v) should be indicated.

a. If the same voltage reading exists, go on to

Step 3.

b. If the voltage output is no longer correct, a

bad ground path exists between the sensor
andthe engine ground. Touch the black lead at
various points, backtracking from the engine
ground back toward the sensor, watching for a
voltage change at each location. If the correct
voltage reading reappears at some point,
check for a problem (rust, corrosion, loose
joint or connection) between that point and
the previous checkpoint. For example, if the
reading is too low at points on the crankcase,
but correct voltage is indicated when the black
lead is touched to the skin of the muffler, the
flange joints at the exhaust ports become
suspect.

3. With the sensor still hot (minimum of 400°C,
752°F), switch the meter to the Rx1K or Rx2K
scale and check the resistance between the sensor
lead and the sensor case. It should be less than

ΩΩ

2.0 K

Ω.

ΩΩ

a. If the resistance is less than 2.0 K

Step 4.

b. If the resistance is greater than 2.0 K

oxygen sensor is bad, replace it.

4. Allow the sensor to cool (less than 60°C, 140°F)
and retest the resistance with the meter set on the
Rx1M scale. With sensor cool, the resistance
should be greater than 1.0 M

a. If the resistance is greater than 1.0 M

Step 5.

ΩΩ

Ω.

ΩΩ

ΩΩ

Ω go to

ΩΩ

ΩΩ

Ω, the

ΩΩ

ΩΩ

Ω go to

ΩΩ

5B

5B.11

Section 5B
EFI Fuel System

b. If the resistance is less than 1.0 M

sensor is bad, replace it.

5. With the oxygen sensor disconnected and
engine not running, disconnect the main
harness connector from the ECU and set the
meter to the Rx1 scale. Check the circuit
continuity as follows:

“24 Pin” (MSE 1.0) Plastic-Cased ECU: Check
for continuity from pin #15 of the ECU
connector (see page 5B.26) to the shell of the
oxygen sensor, and from pin #11 to the sensor
connector terminal of the main harness. Both
tests should indicate continuity.

“32 Pin” (MSE 1.1) Plastic-Cased ECU: Check
for continuity from pin #19 of the ECU
connector (see page 5B.29) to the shell of the
oxygen sensor, and from pin #20 to the sensor
terminal of the main harness. Both tests should
indicate continuity.

a. If there is no continuity displayed in either

of the tests, check the harness circuit for
breaks or damage, and the connections for
poor contact, moisture, or corrosion. If no
continuity was found in the first test, also
check for a poor/broken ground path back
through the exhaust system, engine, and
mounting (sensor is grounded through its
shell).

ΩΩ

Ω, the

ΩΩ

2. Loosen and remove the oxygen sensor from the
exhaust manifold/muffler assembly.

3. Apply anti-seize compound sparingly to
threads of new oxygen sensor, if none already
exists. DO NOT get any on the tip as it will
contaminate the sensor. Install sensor and
torque to 50-60 N·m (37-44 ft. lb.).

4. Reconnect the lead to the wiring harness
connector. Make sure it can not contact hot
surfaces, moving parts, etc.

5. Test run the engine.

Electrical Relay

Figure 5B-11. Electrical Relay.

b. If continuity is indicated, go to step 6.

6. With the key switch in the ‘‘on/run’’ position,
using a high impedance voltmeter, check the
voltage from the wiring harness oxygen sensor
connector to the engine ground location. Look
for a steady voltage from 350-550 mv
(0.35 - 0.55 v).

a. If the voltage reading is not as specified,

move the black voltmeter lead to the
negative post of the battery, to be certain of
a good ground. If the voltage is still not
correct, the ECU is probably bad.

b. If the voltage readings are correct, clear the

fault codes and run the engine to check if
any fault codes reappear.

T o Replace Oxygen Sensor

1. Disconnect the oxygen sensor connector from
the wiring harness.

5B.12

General

The electrical relay is used to supply power to the
injectors, coil, and fuel pump. When the key switch is
turned “on” and all safety switch requirements met,
the relay provides 12 volts to the fuel pump circuit,
injectors, and ignition coils. The fuel pump circuit is
continuously grounded, so the pump is immediately
activated and pressurizes the system. Activation of the
ignition coils and fuel injectors is controlled by the
ECU, which grounds their respective ground circuits
at the proper times.

Service

A malfunctioning relay can result in starting or
operating difficulties. The relay and related wiring can
be tested as follows:

1. Disconnect the relay connector plug from the
relay.

Section 5B

EFI Fuel System

2. Connect the black lead of VOA meter to a chassis
ground location. Connect the red lead to the #86
terminal in relay connector (see Figure 5B-12). Set
meter to test resistance (Rx1). T urn ignition
switch from “off” to “on.” Meter should indicate
continuity (ground circuit is completed) for 1 to 3
seconds. T urn key switch back off.

a. Clean the connection and check wiring if

circuit was not completed.

Terminal #85 ­Ignition Switch
Voltage

Terminal #87A ­Not used

Terminal #30 ­Permanent Battery Voltage

Terminal #87 ­Feed To Ignition
Coils, Fuel
Injectors, and
Fuel Pump

Terminal #86 ­ECU Controlled
Ground

Figure 5B-12. Relay Connector.

3. Set meter for DC voltage. Touch red tester lead
to the #30 terminal in relay connector. A
reading of 12 volts should be indicated at all
times.

Terminal #86 - ECU
Controlled Ground

Terminal
#87A ­Not used

Permanent Battery Voltage

Terminal #87 ­Feed To
Ignition Coils,
Fuel Injectors,
and Fuel Pump

Terminal #85 ­Ignition Switch
Voltage

Terminal #30 -

Figure 5B-13. Relay Terminal Details.

5. Connect an ohmmeter (Rx1 scale) between the
#85 and #86 terminals in the relay. There should
be continuity. See Figure 5B-13.

6. Attach ohmmeter leads to the #30 and #87
terminals in relay. First, there should be no
continuity. Using a 12 volt power supply, connect
the positive (+) lead to the #85 terminal and touch
the negative (-) lead to the #86 terminal. When 12
volts is applied, the relay should activate and
continuity should exist between the #30 and #87
terminals. Repeat the test several times. If, at any
time the relay fails to activate the circuit, replace
the relay.

5B

4. Connect the red lead of meter to the #85
terminal in relay connector. Turn key switch to
the “on” position. Battery voltage should be
present.

a. No voltage present indicates a problem

with the key switch, in the wiring, or at the
connector.

b. If voltage is present, the wiring to the

connector is good. Turn the ignition switch
‘‘off’’ and proceed to Step 5 to test therelay.

Fuel Injectors

Figure 5B-14. Style 1 Fuel Injector.

5B.13

Section 5B
EFI Fuel System

1

2

3

Figure 5B-15. Style 2 Fuel Injector.

General

The fuel injectors mount into the throttle body/intake
manifold, and the fuel rail attaches to them at the top
end. Replaceable O-Rings on both ends of the injector
prevent external fuel leakage and also insulate it from
heat and vibration. A special clip connects each
injector to the fuel rail and holds it in place. The
O-Rings should be replaced anytime the injector is
removed.

When the key switch is on and the relay is closed, the
fuel rail is pressurized, and voltage is present at the
injector. At the proper instant, the ECU completes the
ground circuit, energizing the injector. The valve
needle in the injector is opened electromagnetically,
and the pressure in the fuel rail forces fuel down
through the inside. The “director plate” at the tip of
the injector (see inset) contains a series of calibrated
openings which directs the fuel into the manifold in a
cone-shaped spray pattern.

4

Multi-Orifice
Director Plate With
Calibrated Opening

1. Filter Strainer In
Fuel Supply

2. Electrical Connection

3. Solenoid Winding

Figure 5B-16. Fuel Injector Details.

The injector is opened and closed once for each
crankshaft revolution, however only one-half the total
amount of fuel needed for one firing is injected during
each opening. The amount of fuel injected is
controlled by the ECU and determined by the length
of time the valve needle is held open, also referred to
as the “injection duration” or “pulse width”. It may
vary in length from 1.5-8 milliseconds depending on
the speed and load requirements of the engine.

5

6

7

4. V alve Housing

5. Armature

6. V alve Body

7. V alve Needle

5B.14

Service

Injector problems typically fall into three general
categories: electrical, dirty/clogged, or leakage. An
electrical problem usually causes one or both of the
injectors to stop functioning. Several methods may be
used to check if the injectors are operating.

1. With the engine running at idle, feel for
operational vibration, indicating that they are
opening and closing.

2. When temperatures prohibit touching, listen for a
buzzing or clicking sound with a screwdriver or
mechanic’s stethoscope (see Figure 5B-17).

Section 5B

EFI Fuel System

Listen Here

Figure 5B-17. Checking Injectors.

3. Disconnect the electrical connector from an
injector and listen for a change in idle
performance (only running on one cylinder) or a
change in injector noise or vibration.

If an injector is not operating, it can indicate either a
bad injector, or a wiring/electrical connection
problem. Check as follows:

NOTE: Do not apply voltage to the fuel injector(s).

Excessive voltage will burn out the
injector(s). Do not ground the injector(s) with
the ignition “on.” Injector(s) will open/turn
on if relay is energized.

a. If flashing occurs, use an ohmmeter (Rx1

scale) and check the resistance of each
injector across the two terminals. Proper
resistance is 12-20
correct, check whether the connector and
injector terminals are making a good
connection. If the resistance is not correct,
replace the injector following steps 1-8 and
13-16 below.

b. If no flashing occurs, reattach the connectors

to both injectors. Disconnect the main harness
connector from the ECU and the connector
from the relay. Set the ohmmeter to the Rx1
scale and check the injector circuit resistance
as follows:

“24 Pin” (MSE 1.0) Plastic-Cased ECU:

Check the resistance between relay terminal
#87 and pin #16 in the main connector. Then
check the resistance between relay terminal
#87 and pin #17. Resistance should be 4-15
for each circuit.

“32 Pin” (MSE 1.1) Plastic-Cased ECU:

Check the resistance between relay terminal
#87 and pin #14 in the main connector. Then
check the resistance between relay terminal
#87 and pin #15. Resistance should be

ΩΩ

4-15

Ω for each circuit.

ΩΩ

ΩΩ

Ω. If injector resistance is

ΩΩ

5B

ΩΩ

Ω

ΩΩ

Figure 5B-18. Volt Noid Light.

1. Disconnect the electrical connector from both
injectors. Plug a 12 volt noid light (part of EFI
Service Kit, see Section 2) into one connector.

2. Make sure all safety switch requirements are met.
Crank the engine and check for flashing of the
test light. Repeat test at other connector.

Check all electrical connections, connectors, and
wiring harness leads if resistance is incorrect.

Injector leakage is very unlikely, but in those rare
instances it can be internal (past the tip of the valve
needle), or external (weeping around the injector
body). See Figure 5B-19. The loss of system pressure
from the leakage can cause hot restart problems and
longer cranking times. To check for leakage it will be
necessary to loosen or remove the blower housing
which may involve removing the engine from the unit.

5B.15

Section 5B
EFI Fuel System

Check For Leaks

Figure 5B-19. Injector Inspection Points.

10. Remove the manifold mounting bolts and separate
the throttle body/manifold from the engine
leaving the TPS, fuel rail, air baffle, injectors and
line connections intact. Discard the old gaskets.

11. Position the manifold assembly over an
appropriate container and turn the key switch
“on” to activate the fuel pump and pressurize the
system. Do not turn switch to “start” position.

12. If either injector exhibits leakage of more than two
to four drops per minute from the tip, or shows
any sign of leakage around the outer shell, turn
the ignition switch off and replace the injector as
follows.

1. Engine must be cool. Depressurize fuel system
through test valve in fuel rail.

2. Disconnect spark plug leads from spark plugs.

3. Remove the air cleaner outer cover, inner wing
nut, element cover and air cleaner element/
precleaner. Service air cleaner components as
required.

4. Remove the two screws securing the air cleaner
base to the throttle body manifold. Remove the
air cleaner base to permit access to the injectors.
Check condition of air cleaner base gasket,
replace if necessary.

5. Remove the flywheel screen if it overlaps the
blower housing.

6. If the engine has a radiator-type oil cooler
mounted to the blower housing, remove the two
oil cooler mounting screws.

7. Remove the blower housing mounting screws.
Note the location of the plated (silver) screw
attaching the rectifier/regulator ground lead.
Remove the blower housing.

8. Thoroughly clean the area around and including
the throttle body/manifold and the injectors.

9. Disconnect the throttle linkage and damper
spring from the throttle lever. Disconnect the TPS
lead from the harness.

13. Depressurize the fuel system following the
procedure in the fuel warning on page 5B.2.
Remove the two fuel rail mounting screws.

14. Clean any dirt accumulation from the sealing/
mounting area of the faulty injector(s) and
disconnect the electrical connector(s).

15. Pull the retaining clip off the top of the injector(s).
Disconnect the fuel rail and remove the injector(s)
from the manifold.

16. Reverse the appropriate procedures to install the
new injector(s) and reassemble the engine. Use
new O-Rings any time an injector is removed (new
replacement injectors include new O-Rings).
Lubricate O-Rings lightly with oil. Torque the fuel
rail and blower housing mounting screws to

3.9 N·m (35 in. lb.), and the intake manifold and
air cleaner mounting screws to 9.9 N·m
(88 in. lb.).

Injector problems due to dirt or clogging are generally
unlikely due to the design of the injectors, the high fuel
pressure, and the detergent additives in the gasoline.
Symptoms that could be caused by dirty/clogged
injectors include rough idle, hesitation/stumble during
acceleration, or triggering of fault codes related to fuel
delivery. Injector clogging is usually caused by a
buildup of deposits on the director plate, restricting
the flow of fuel, resulting in a poor spray pattern.
Some contributing factors to injector clogging include
higher than normal operating temperatures, short
operating intervals, and dirty, incorrect, or poor quality
fuel. Cleaning of clogged injectors is not
recommended; they should be replaced. Additives and
higher grades of fuel can be used as a preventative
measure if clogging has been a problem.

5B.16

Section 5B

EFI Fuel System

Ignition System

General

A high-voltage, solid-state, battery ignition system is
used with the EFI system. The ECU controls the
ignition output and timing through transistorized
control of the primary current delivered to the coils.
Based on input from the speed sensor, the ECU
determines the correct firing point for the speed at
which the engine is running. At the proper instant, it
releases the flow of primary current to the coil. The
primary current induces high voltage in the coil
secondary, which is then delivered to the spark plug.
Each coil fires every revolution, but every other spark
is "wasted".

Service

Except for removing the spark plug lead by
unscrewing it from the secondary tower (see Figure
5B-20), no coil servicing is possible. If a coil is
determined to be faulty, replacement is necessary. An
ohmmeter may be used to test the wiring and coil
windings.

2. Disconnect connector from relay and locate
terminal #87 in connector.

3. Using an ohmmeter set on the Rx1 scale, check
the resistance in circuits as follows:

"24 Pin" (MSE 1.0) Plastic-Cased ECU: Check
between terminal #87 and pin #22 for coil #1.
Repeat the test between terminal #87 and pin #23
for coil #2.

"32 Pin" (MSE 1.1) Plastic-Cased ECU: Check
between terminal #87 and pin #30 for coil #1.
Repeat the test between terminal #87 and pin #31
for coil #2.

A reading of 1.8-4.0
the wiring and coil primary circuits are OK.

a. If reading(s) are not within specified range,

check and clean connections and retest.

b. If reading(s) are still not within the specified

range, test the coils separately from main
harness as follows:

ΩΩ

Ω in each test indicates that

ΩΩ

5B

Figure 5B-20. Ignition Coil.

NOTE: Do not ground the coils with the ignition

‘‘on,’’ as they may overheat or spark.

Testing

1. Disconnect the main harness connector from the
ECU.

"24 Pin" (MSE 1.0) Plastic-Cased ECU: Locate
pins #22 and #23 in the 24 pin connector. See page
5B.26.

"32 Pin" (MSE 1.1) Plastic Cased ECU: Locate
pins #30 and #31 in the 32 pin connector. See page
5B.29.

1) Disconnect the red and black primary
leads from the coil terminals.

2) Connect an ohmmeter set on the Rx1
scale to the primary terminals. Primary
resistance should be 1.8-2.5

3) Disconnect the secondary lead from the
spark plug. Connect an ohmmeter set on
the Rx10K scale between the spark plug
boot terminal and the red primary
terminal. Secondary resistance should
be 13,000-17,500

4) If the secondary resistance is not within
the specified range, unscrew the spark
plug lead nut from the coil secondary
tower and remove the plug lead. Repeat
step b. 3, testing from the secondary tower
terminal to the red primary terminal. If
resistance is now correct, the coil is good,
but the spark plug lead is faulty, replace
the lead. If step b. 2 resistance was
incorrect and/or the secondary resistance
is still incorrect, the coil is faulty and
needs to be replaced.

ΩΩ

Ω.

ΩΩ

ΩΩ

Ω.

ΩΩ

5B.17

Section 5B
EFI Fuel System

Spark Plugs

EFI engines are equipped with Champion® RC12YC
(Kohler Part No. 12 132 02-S) resistor spark plugs.
Equivalent alternate brand plugs can also be used, but
must be resistor plugs or permanent damage to the
ECU will occur, in addition to affecting operation.
Proper spark plug gap is 0.76 mm (0.030 in.).

Wiring Harness

The wiring harness used in the EFI system connects
the electrical components, providing current and
ground paths for the system to operate. All input and
output signaling occurs through a special all weather
connector that attaches and locks to the ECU (see
Figures 5B-21 and 5B-22).

The condition of the wiring, connectors, and terminal
connections is essential to system function and
performance. Corrosion, moisture, and poor
connections are more likely the cause of operating
problems and system errors than an actual
component. Refer to the ‘‘Troubleshooting –
Electrical’’ section for additional information.

Battery Charging System

EFI engines are equipped with either a 15 or 25 amp
charging system to accommodate the combined
electrical demands of the ignition system and the
specific application. Charging system troubleshooting
information is provided in Section 8.

Fuel Components

Fuel Pump

Figure 5B-21. “24 Pin” (MSE 1.0) Plastic-Cased
ECU Connector.

Figure 5B-22. “32 Pin” (MSE 1.1) Plastic-Cased
ECU Connector.

Internal

Figure 5B-23. Fuel Pump Styles.

General

An electric fuel pump is used to transfer fuel in the
EFI system. Depending on the application, the pump
may be inside the fuel tank, or in the fuel line near the
tank. The pumps are rated for a minimum output of
25 liters per hour at 39 psi. The pumps have an
internal 60-micron filter. In addition, the in-tank style
pumps will have a pre-filter attached to the inlet. In­line pump systems may also have a filter between the
tank and the pump on the pickup/low pressure side.
The final fuel filter is covered separately on page
5B-21.

When the key switch is turned “on” and all safety
switch requirements are met, the ECU, through the
relay activates the fuel pump, which pressurizes the
system for start-up. If the key switch is not promptly
turned to the “start” position, the engine fails to start,
or the engine is stopped with the key switch “on” (as
in the case of an accident), the ECU switches off the

External

5B.18

Section 5B

EFI Fuel System

pump preventing the continued delivery of fuel. In
this situation, the MIL will go on, but it will go back
off after 4 cranking revolutions if system function is
OK. Once the engine is running, the fuel pump
remains on.

Service

The fuel pumps are non-serviceable and must be
replaced if determined to be faulty. If a fuel delivery
problem is suspected, make certain the pump is being
activated through the relay, all electrical connections
are properly secured, the fuses are good, and a
minimum of 7.0 volts is being supplied. If during
cranking, voltage drops below 7.0 volts, a reduction of
fuel pressure may occur resulting in a lean starting
condition. If required, testing of the fuel pump and
relay may be conducted.

1. Connect the black hose of Pressure Tester (part of
EFI Service Kit, see Section 2) to the test valve in
the fuel rail. Route the clear hose into a portable
gasoline container or the equipment fuel tank.

2. Turn on the key switch to activate the pump and
check the system pressure on the gauge. If system
pressure of 39 psi ± 3 is observed, the relay, fuel
pump, and regulator are working properly. Turn
key switch off and depress the valve button on
the tester to relieve the system pressure.

b. If the voltage was below 7, test the wiring

harness and relay as covered in the
‘‘Electrical Relay’’ section.

4. If voltage at the plug was good, and there was
continuity across the pump terminals, reconnect
the plug to the pump, making sure you have a
good connection. Turn on the key switch and
listen for the pump to activate.

a. If the pump starts, repeat steps 1 and 2 to

verify correct pressure.

b. If the pump still does not operate, replace it.

Fuel Pressure Regulator

5B

a. If the pressure is too high, and the regulator

is outside the tank (just down line from the
pump), check that the return line from the
regulator to the tank is not kinked or
blocked. If the return line is good, replace
the regulator (see ‘‘Regulator Service’’ on
page 5B.20).

b. If the pressure is too low, install in-line ‘‘T’’

between the pump and the regulator and
retest the pressure at that point. If it is too low
there also, replace the fuel pump.

3. If the pump did not activate (step 2), disconnect
the plug from the fuel pump. Connect a DC
voltmeter across the terminals in the plug, turn
on the key switch and observe if a minimum of 7
volts is present. If voltage is between 7 and 14,
turn key switch off and connect an ohmmeter
between the terminals on the pump to check for
continuity.

a. If there was no continuity between the pump

terminals, replace the fuel pump.

Figure 5B-24. External Fuel Pressure Regulators.

Figure 5B-25. Internal Fuel Pressure Regulators.

5B.19

Section 5B
EFI Fuel System

General

The fuel pressure regulator assembly maintains the
required operating system pressure of 39 psi ± 3. A
rubber-fiber diaphragm (see Figure 5B-26) divides the
regulator into two separate sections; the fuel chamber
and the pressure regulating chamber. The pressure
regulating spring presses against the valve holder
(part of the diaphragm), pressing the valve against the
valve seat. The combination of atmospheric pressure
and regulating spring tension equals the desired
operating pressure. Any time the fuel pressure against
the bottom of the diaphragm exceeds the desired (top)
pressure, the valve opens, relieving the excess

pressure, returning the excess fuel back to the tank.

Pressure
Regulating
Spring

Valve

Inlet Port

Return Port (To Tank)

Figure 5B-26. Fuel Pressure Regulator Details.

Pressure
Regulating
Chamber

Diaphragm

Valve Seat

Fuel Chamber

Outlet Port
(To Fuel Rail)

a. Remove the two screws securing the

mounting bracket to the regulator housing.
Remove the O-Ring and pull the regulator out
of the housing.

b. Remove the snap ring and remove regulator

from base/holder.

Internal (In-Tank) Regulator -

Remove the three screws securing the retaining
ring and regulator in the base/holder assembly.
Grasp and pull the regulator out of the base/
holder. See Figure 5B-28.

Service

Depending on the application, the regulator may be
located in the fuel tank along with the fuel pump, or
outside the tank just down line from the pump. The
regulator is a sealed, non-serviceable assembly. If it is
faulty, it must be separated from the base/holder
assembly and replaced as follows:

1. Shut engine off, make sure engine is cool, and
disconnect the negative (-) battery cable.

2. Depressurize fuel system through test valve in
fuel rail (see fuel warning on page 5B.2).

3. Access the regulator assembly as required and
clean any dirt or foreign material away from the
area.

4. External Regulator -
Based upon the style of regulator used: See
Figure 5B-27:

Figure 5B-27. External Regulators and Base/
Holders.

Figure 5B-28. Internal (In-T ank) Regulator and
Base/Holder .

5. Always use new O-Rings and hose clamps when
installing a regulator. A new replacement
regulator will have new O-Rings already
installed. Lubricate the O-Rings (external
regulator) with light grease or oil.

5B.20

Section 5B

EFI Fuel System

6. Install the new regulator by carefully pushing
and rotating it slightly into the base or housing.

a. External Regulators with Square Base

Housing Only; Install a new O-Ring between
the regulator and the mounting bracket. Set
the mounting bracket into position.

b. Secure the regulator in the base with the

original retaining ring or screws. Be careful
not to dent or damage the body of the
regulator as operating performance can be
affected.

7. Reassemble and connect any parts removed in
step 3.

8. Reconnect the negative (-) battery cable.

9. Recheck regulated system pressure at fuel rail test
valve.

Fuel Filter

EFI engines use a high-volume, high-pressure, 10-15
micron, in-line fuel filter.

Fuel Rail

Fuel Rail

TPS

Locking Cups

Figure 5B-30. Throttle Body/Intake Manifold.

General

The fuel rail is a formed tube assembly that feeds fuel
to the top of the injectors. The tops of the injectors fit
into formed cups in the fuel rail. When the rail is
fastened to the manifold, the injectors are locked into
place. A small retaining clip provides a secondary
lock. Incorporated into the fuel rail is a pressure relief/
test valve for testing operating pressure or relieving
fuel system pressure for servicing. The fuel supply
line is attached to the barbed end of the fuel rail with
an Oetiker hose clamp.

Fuel Injector

5B

Figure 5B-29. In-Line Fuel Filter.

Service

Filter replacement is recommended every 1500 hours
of operation or more frequently under extremely
dusty or dirty conditions. Use only the specified filter,
and install it according to the directional arrows. Do
not use a substitute filter as operating performance
and safety can be affected. Relieve system pressure
through the safety valve in the fuel rail before
servicing.

Service

The fuel rail is mounted to the throttle body/intake
manifold. No specific servicing is required unless
operating conditions indicate that it needs internal
cleaning or replacement. It can be detached by
removing the two mounting screws and the injector
retaining clips. Thoroughly clean the area around all
joints and relieve any pressure before starting any
disassembly.

Fuel Line

Figure 5B-31. High Pressure Fuel Line.

5B.21

Section 5B
EFI Fuel System

General

Special low permeation high-pressure fuel line with
an SAE 30 R9 rating is required for safe and reliable
operation, due to the higher operating pressure of the
EFI system. If hose replacement is necessary, order
Fuel Line Service Kit Part No. 25 111 37-S (containing
60” of high-pressure hose and 10 Oetiker clamps), or
use only the type of hose specified. Special Oetiker
clamps (Kohler Part No. 24 237 05-S) are used on all
fuel line connections to prevent tampering and safety
hazards with the high fuel pressure. The old clamp
must be cut to open a connection, so replacement is
necessary each time. Oetiker Clamp Pliers (part of EFI
Service Kit, see Section 2) is used to crimp the
replacement clamps.

CAUTION:

Fuel lines between the fuel pump and fuel rail must be made
from SAE 30 R9 fuel line. Standard fuel line (SAE 30 R7)
may only be used between the fuel tank and pump (5/16”
ID) and for the return line from the pressure regulator to
the tank (1/4” ID). All high-pressure fuel line connections
must be secured with Oetiker clamps (Kohler Part No.
24 237 05-S), installed/crimped with the corresponding
pliers.

Throttle Body/Intake Manifold Assembly

Service

The throttle body/intake manifold is serviced as an
assembly, with the throttle shaft, TPS, throttle plates,
and idle speed adjusting screw installed. The throttle
shaft rotates on needle bearings (non-serviceable),
capped with rubber seals to prevent air leaks. A
throttle shaft repair kit is available to replace the shaft
if worn or damaged. The appropriate “TPS
Initialization Procedure” must be performed after any
throttle shaft service.

Idle Speed Adjustment (RPM)

General

The idle speed is the only adjustment that may be
performed on the EFI system. The standard idle speed
setting for EFI engines is 1500 RPM, but certain
applications might require a different setting. Check
the equipment manufacturer’s recommendation.

For starting and warm up, the ECU will adjust the fuel
and ignition timing, based upon ambient temperature,
engine temperature, and loads present. In cold
conditions, the idle speed will probably be higher than
normal for a few moments. Under other conditions,
the idle speed may actually start lower than normal,
but gradually increase to the established setting as
operation continues. Do not attempt to circumvent
this warm up period, or readjust the idle speed during
this time. The engine must be completely warmed up,
in closed loop operating mode for accurate idle
adjustment.

Figure 5B-32. Upper Throttle Body/Intake Manifold
Details.

General

The EFI engines have no carburetor, so the throttle
function (regulate incoming combustion airflow) is
incorporated in the intake manifold assembly. The
manifold consists of a one-piece aluminum casting
which also provides mounting for the fuel injectors,
throttle position sensor, fuel rail, air baffle, idle speed
screw, and air cleaner assembly.

5B.22

Adjustment Procedure

1. Make sure there are no fault codes present in the
ECU memory.

2. Start the engine and allow it to fully warm up
and establish closed looped operation
(approximately 5-10 min.).

3. Place the throttle control in the ‘‘idle/slow’’
position and check the idle speed with a
tachometer. Turn the idle speed screw in or out as
required to obtain 1500 RPM, or the idle speed
specified by the equipment manufacturer. See
Figure 5B-33.

4. The idle speed adjustment can affect the high idle
speed setting. Move the throttle control to the full
throttle position and check the high idle speed.
Adjust as necessary to 3750 RPM, or the speed
specified by the equipment manufacturer.

Idle Speed
Screw

Section 5B

EFI Fuel System

Throttle
Linkage

Figure 5B-34. Throttle Linkage/Governor Lever
Connection.

Linkage
Bushing

Damper
Spring

Figure 5B-33. Idle Speed Screw Details.

Initial Governor Adjustment

The initial governor adjustment is especially critical
on EFI engines because of the accuracy and sensitivity
of the electronic control system. Incorrect adjustment
can result in overspeed, loss of power, lack of
response, or inadequate load compensation. If you
encounter any of these symptoms and suspect them to
be related to the governor setting, the following
should be used to check and/or adjust the governor
and throttle linkage.

If the governor/throttle components are all intact, but
you think there may be a problem with the
adjustment, follow Procedure A to check the setting. If
the governor lever was loosened or removed, go
immediately to Procedure B to perform the initial
adjustment.

A. Checking the Initial Adjustment

1. Unsnap the plastic linkage bushing attaching the
throttle linkage to the governor lever. See Figure
5B-34. Unhook the damper spring from the lever,
separate the linkage from the bushing, and
remove the bushing from the lever. Mark the hole
position and unhook the governor spring from
the governor lever.

2. Check if the engine has a high-speed throttle stop
screw installed in the manifold casting boss. See
Figure 5B-35.

5B

High-Speed
Throttle Stop
Screw

Figure 5B-35. Throttle Details.

a. On engines with a stop screw, pivot the

throttle shaft and plate into the “Full Throttle”
position, so the tang of the throttle shaft plate
is against the end of the high-speed stop
screw. See Figure 5B-35. Temporarily clamp in
this position.

5B.23

Section 5B
EFI Fuel System

Figure 5B-36. Inserting Feeler Gauge (Engines
Without Stop Screw).

b. On engines without a stop screw, pivot the

throttle shaft and plate assembly into the
“Full Throttle” position. Insert a 1.52 mm
(0.060 in.) feeler gauge between the
tang of the throttle shaft plate and the
underside of the manifold boss. Use a
locking pliers (needle nose works best) to
temporarily clamp the parts in this position.
See Figure 5B-36.

3. Rotate the governor lever and shaft
counterclockwise until it stops. Use only enough
pressure to hold it in that position.

B. Setting the Initial Adjustment

1. Check the split where the clamping screw goes
through the governor lever. See Figure 5B-38.
There should be a gap of at least 1/32". If the tips
are touching and there is no gap present, the lever
should be replaced. If not already installed,
position the governor lever on the cross shaft, but
leave the clamping screw loose.

Figure 5B-38. Checking ‘‘Split’’ of Clamp.

2. Follow the instructions in Step 2 of ‘‘Checking the
Initial Adjustment,’’ then reattach the throttle
linkage to the governor lever with the bushing
clip. It is not necessary to reattach the damper or
governor springs at this time.

4. Check how the end of the throttle linkage aligns
with the bushing hole in the governor lever. See
Figure 5B-37. It should fall in the center of the
hole. If it doesn’t, perform the adjustment
procedure as follows.

Figure 5B-37. Throttle Link in Center of Hole.

3. Insert a nail into the hole in the top of the cross
shaft. Using light pressure, rotate the governor
shaft counterclockwise as far as it will turn, then
torque the hex nut on the clamping screw to

6.8 N·m (60 in. lb.). See Figure 5B-39. Make sure
that the governor arm has not twisted up or
down after the nut has been tightened.

Figure 5B-39. Adjusting Governor Shaf t.

5B.24

Section 5B

EFI Fuel System

4. Verify that the governor has been set correctly.
With the linkage still retained in the “Full
Throttle” position (Step 2), unsnap the bushing
clip, separate the linkage from the bushing, and
remove the bushing from the lever. Follow Steps
3 and 4 in ‘‘Checking the Initial Adjustment’’.

5. Reconnect the dampening spring into its
governor lever hole from the bottom. Reinstall
the bushing and reattach the throttle linkage. See
Figure 5B-34. Reattach the governor spring in the
marked hole.

6. Start the engine and allow it to fully warm up
and establish closed loop operation
(approximately 5-10 min.). Check the speed
settings and adjust as necessary, first the low idle
speed, and then the high-speed setting.

Troubleshooting

General

When troubleshooting a problem on an engine with
EFI, basic engine operating problems must be
eliminated first before faulting the EFI system
components. What appears to be an EFI problem
could be something as simple as a fuel tank with
debris in the bottom or a plugged vent. Be sure the
engine is in good mechanical operating condition and
all other systems are operating properly before
attempting to troubleshoot the EFI system.

Engine starts hard or fails to start when hot

1. Faulty spark plugs

2. Fuel pump not running

3. Fuel pressure low

4. Insufficient fuel delivery

5. TPS offset incorrect (Initialization)

6. Speed sensor loose or faulty

7. TPS faulty

8. Engine temp sensor faulty

9. Faulty injectors

Engine stalls or idles roughly (cold or warm)

1. Faulty spark plugs

2. Insufficient fuel delivery

3. TPS offset incorrect

4. TPS faulty

5. Faulty engine temperature sensor

6. Faulty injectors

Engine misses, hesitates, or stalls under load

1. Fuel injector(s), fuel filter, fuel line, or fuel pick­up dirty/restricted

2. Dirty air cleaner

3. Insufficient fuel pressure or fuel delivery

4. Vacuum (intake air) leak

5. Improper governor setting, adjustment or
operation

6. Speed sensor malfunction

7. TPS faulty, mounting problem or "TPS
Initialization Procedure" incorrect

8. Bad coil(s), spark plug(s), or wires

5B

Troubleshooting Guide

Engine starts hard or fails to start when cold

1. Fuel pump not running

2. Faulty spark plugs

3. Old/stale fuel

4. Incorrect fuel pressure

5. Speed sensor loose or faulty

6. TPS offset incorrect (initialization)

7. TPS faulty

8. Engine temp sensor faulty

9. Faulty coils

10. Low system voltage

11. Faulty injectors

Low Power

1. Faulty/malfunctioning ignition system

2. Dirty air filter

3. Insufficient fuel delivery

4. Improper governor adjustment

5. Plugged/restricted exhaust

6. One injector not working

7. Basic engine problem exists

8. TPS faulty or mounting exists

9. Throttle plates in throttle body/intake manifold
not fully opening to WOT stop (if so equipped)

5B.25

Section 5B
EFI Fuel System

Electrical System

The EFI system is a 12 VDC negative ground system,
designed to operate down to a minimum of 7.0 volts.
If system voltage drops below this level, the operation
of voltage sensitive components such as the ECU, fuel
pump, and injectors will be intermittent or disrupted,
causing erratic operation or hard starting. A fully
charged, 12 volt battery with a minimum of 350 cold
cranking amps is important in maintaining steady and
reliable system operation. Battery condition and state
of charge should always be checked first when
troubleshooting an operational problem.

Keep in mind that EFI-related problems are more
often caused by the wiring harness or connections
than by the EFI components. Even small amounts of
corrosion or oxidation on the terminals can interfere
with the milliamp currents used in system operation.

Cleaning the connectors and grounds will solve
problems in many cases. In an emergency situation,
simply disconnecting and reconnecting the connectors
may clean up the contacts enough to restore operation,
at least temporarily.

If a fault code indicates a problem with an electrical
component, disconnect the ECU connector and test for
continuity between the component connector
terminals and the corresponding terminals in the ECU
connector using an ohmmeter. Little or no resistance
should be measured, indicating that the wiring of that
particular circuit is OK. An illustrated listing of
numerical terminal locations, for each style of ECU
connector is provided on pages 5B.26 and 5B.29.

NOTE: When performing voltage or continuity tests,

“24 Pin” (MSE 1.0) Plastic-Cased ECU Systems

Pin #

1
2
3
4
5
6
7
8

9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

Permanent Battery Voltage
Switched Ignition Voltage
Safety Switch
Throttle Position Sensor (TPS) and Temperature Sensor Ground

Not Used

Oil Temperature Sensor Input

Not Used
Throttle Position Sensor (TPS) Input
Speed Sensor Input
Speed Sensor Ground
Oxygen Sensor Input

Not Used (Oxygen Sensor Ground if needed)
Diagnostic Line
Throttle Position Supply Voltage
Battery Ground
Injector 1 Output
Injector 2 Output
Main Relay Output
Malfunction Indicator Light (MIL)

Not Used (Tach Output if needed)

Not Used
Ignition Coil #1 Output
Ignition Coil #2 Output
TPS Initialization Terminal

Function

avoid putting excessive pressure on or
against the connector pins. Flat pin probes
are recommended for testing to avoid
spreading or bending the terminals.

1
2

3
4

5
6
7

8

9
10
11

12

13
14
15

16
17

18
19
20

21
22

23
24

5B.26

“32 Pin” (MSE 1.1) Plastic-Cased ECU Systems

Section 5B

EFI Fuel System

Pin #

1
2
3
4
5
6
7
8

9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32

Function

Permanent Battery Voltage
Switched Battery Voltage
TPS Set; “Auto-Learn” Initialization Terminal
Throttle Position Sensor (TPS) and Temperature Sensor Ground

Not Used

Oil Temperature Sensor Input

Not Used
Throttle Position Sensor (TPS) Input
Speed Sensor Input (+)
Speed Sensor Ground (-)

Not Used

Not Used

Not Used
Injector 1 Output
Injector 2 Output

Not Used
Diagnostic Line
Throttle Position Sensor Supply Voltage
Battery Ground
Oxygen Sensor Input
Battery Ground (secondary)

Not Used

Not Used

Not Used
Safety Switch Input

Not Used

Not Used
Main Relay Output
Malfunction Indicator Light (MIL)
Ignition Coil #1 Output
Ignition Coil #2 Output

Not Used

10
11
12

13
14

15
16

1
2
3
4
5

6

7
8

9

17
18

19
20

21
22

23
24
25

26
27

28
29

30
31

32

5B

5B.29

Section 5B
EFI Fuel System

Fuel System

WARNING: Fuel System Under Pressure!

The fuel system operates under high pressure. System
pressure must be relieved through the test valve in the fuel
rail prior to servicing or removal of any fuel system
components. Do not smoke or work near heaters or other fire
hazards. Have a fire extinguisher handy and work only in a
well-ventilated area.

The function of the fuel system is to provide sufficient
delivery of fuel at the system operating pressure of 39
psi ± 3. If an engine starts hard, or turns over but will
not start, it may indicate a problem with the EFI fuel
system. A quick test will verify if the system is
operating.

1. Disconnect and ground the spark plug leads.

2. Complete all safety interlock requirements and
crank the engine for approximately 3 seconds.

3. Remove the spark plugs and check for fuel at the
tips.

a. If there is fuel at the tips of the spark plugs the

fuel pump and injectors are operating.

b. If there is no fuel at the tips of the spark plugs,

check the following:

1) Make sure the fuel tank contains clean,
fresh, proper fuel.

Fault Codes

The ECU continuously monitors engine operation
against preset performance limits. If the operation is
outside the limits, the ECU activates the MIL and
stores a diagnostic code in its fault memory. If the
component or system returns to proper function, the
ECU will eventually self-clear the fault code and turn
off the MIL. If the MIL stays illuminated, it warns the
customer that dealer service is required. Upon receipt,
the dealer technician can access the fault code(s) to
help determine what portion of the system is
malfunctioning. The 2-digit fault codes available based
upon the style of ECU are listed on pages 5B.31-5B.32.

The codes are accessed through the key switch and
displayed as blinks or flashes of the MIL. Access the
codes as follows:

1. Start with the key switch off.

2. Turn the key switch on-off-on-off-on, leaving it
on in the third sequence. The time between
sequences must be less than 2.5 seconds.

3. Any stored fault codes will then be displayed as a
series of MIL blinks (from 2 to 6) representing the
first digit, followed by a pause, and another series
of blinks (from 1 to 6) for the second digit (see
Figure 5B-40).

a. It’s a good idea to write down the codes as

they appear, as they may not be in numerical
sequence.

5B.30

2) Make sure that the vent in the fuel tank is
open.

3) Make sure the fuel tank valve (if so
equipped) is fully opened.

4) Make sure the battery is supplying proper
voltage.

5) Check that the fuses are good, and that
no electrical or fuel line connections are
damaged or broken.

6) Test fuel pump and relay operation as
described earlier under ‘‘Fuel Pump –
Service.’’

b. Code 61 will always be the last code

displayed, indicating the end of code
transmission. If code 61 appears immediately,
no other fault codes are present.

Example of Diagnostic Display

1. Diagnostic display initiated through ignition key sequencing.

2.

Section 5B

EFI Fuel System

Long Pause

Short Pause

3.

Code 32

4.

5.

6.

7.

3

Long Pause

6

Long Pause

Light remains on at end of transmission

2

Code 61

1

Figure 5B-40.

After the problem has been corrected, the fault codes may be cleared as follows.

1. Disconnect the negative (-) battery cable or the main harness connector for one minute.

2. Reconnect the cable and tighten securely. Start the engine and allow it to run for several minutes. The MIL
should remain off if the problem was corrected, and the fault codes should not reappear (codes 31, 32, 33,
and 34 may require 10-15 minutes of running to reappear).

The following chart lists the fault codes, what they correspond to, and what the visual indications will be.
Following the chart is a list of the individual codes with an explanation of what triggers them, what symptoms
might be expected, and the probable causes.

5B

Diagnostic Code Summary

2DBO

edoC-P

knilB

edoC

-- langiSMPRoNYY
125330PnoitazinorhcnySfossoLYY

220210PelbisualpmIlangiS-SPTNN2
222210PdnuorGottiucriCtrohSronepO-SPTYY
223210PyrettaBottiucriCtrohS-SPTYY
321060PUCEevitcefeDYY
42rosneSdeepSenignEYY9

134710PnaeLootmetsySYY6

elbacilppA

"niP23":ot

)1.1ESM(

-tsyS/UCE

ylnOme

"niP42"

noitpircseDeruliaFronoitcennoC

)0.1ESM(

desaC-citsalP

metsyS/UCE

"niP23"

)1.1ESM(

desaC-citsalP

metsyS/UCE

etoN

Continue on next page.

5B.31

Section 5B
EFI Fuel System

Diagnostic Code Summary cont.

2DBO

edoC-P

knilB

edoC

elbacilppA

"niP23":ot

)1.1ESM(

-tsyS/UCE

ylnOme

"niP42"

noitpircseDeruliaFronoitcennoC

)0.1ESM(

desaC-citsalP

metsyS/UCE

"niP23"

)1.1ESM(

desaC-citsalP

metsyS/UCE

etoN

132310PO
234310PO
335710PhciRootmetsySYY8,7
330200PO
431710PdehcaeRtimiLnoitpadAmumixaMYY8
432710PdehcaeRtimiLnoitpadAmuminiMYY8

247110P

248110P

34A/N

44A/N

150621PtiucriCnepO-1rotcejnIA/NY

151620PdnuorGottiucriCtrohS-1rotcejnIA/NY

152620PyrettaBottiucriCtrohS-1rotcejnIA/NY
253621PtiucriCnepO-2rotcejnIA/NY
254620PdnuorGottiucriCtrohS-2rotcejnIA/NY

2

2

2

dnuorG

yrettaBottrohS

yrettaBotdetrohS:tiucriCrosneSNY3

detceteDytivitcAoN:tiucriCrosneSNN8

timiLreppUtalortnoCrosneSYY8

otdetrohS:tiucriCrosneSerutarepmeT

rotiucriCnepO:tiucriCrosneSerutarepmeT

tesffOSPT-nraelotuAgnitelpmoCeruliaF

timilelbawollamuminimwoleb

tesffoSPT-nraelotuAgnitelpmoCeruliaF

timilelbawollamumixamevoba

YY

YY

A/NY

A/NY

255620PyrettaBottiucriCtrohS-2rotcejnIA/NY
5515619tiucriCnepO-pmaLcitsongaiDA/NY
552561PdnuorGottiucriCtrohS-pmaLcitsongaiDA/NY
553561PyrettaBottiucriCtrohS-pmaLcitsongaiDA/NY
651321PtiucriCnepO-yaleRpmuPA/NY
652321PdnuorGottiucriCtrohS-yaleRpmuPA/NY
653321PyrettaBottiucriCtrohS-yaleRpmuPA/NY

16noissimsnarTedoCfodnEYY

Note:

1. Idle Switch not used.

2. Diagnostic of "TPS - Signal Implausible" is disabled in code.

3. "O2 Sensor Short to Battery" diagnostic detection is disabled with SAS fuel-cutoff calibrated out.

4. Air Temperature Sensor not used.

5. "Temperature Sensor Signal Implausible": diagnostic detection is calibrated out, with TPLAUS set to -50°C.

6. System too Lean used to be "O2 Sensor - Short to Ground (P0131)."

7. "System too Rich" used to be "O2 Sensor Control at Lower Limit (P0019)."

8. Obtainable only with ECU 24 584 28-S or later.

9. Will not blink out.

5B.32

Section 5B

EFI Fuel System

Code: 21
Source: Engine Speed Sensor
Explanation: ECU receiving inconsistent tooth

count signals from speed sensor.

Expected Engine
Response: Possible misfire as ECU attempts

to resynchronize during which time
fuel and spark calculations are not
made.

Possible Causes:

1. Engine Speed Sensor Related
a. Sensor connector or wiring.
b. Sensor loose or incorrect air gap.
c. Flywheel key sheared.

2. Speed Sensor Ring Gear Related
a. Damaged teeth.
b. Varying gap (gear loose/out of alignment).

3. Engine Wiring Harness Related

“24 Pin” (MSE 1.0) Plastic-Cased ECU:

a. Pin circuits 9 and/or 10 wiring or connectors.
b. Shielding for pin circuits 9 and/or 10 damaged

or not properly grounded.

c. Poor or improper grounds in system (battery,

ECU oxygen sensor, shielding, fuel pump,
ignition output).

d. Pin circuits 9 and/or 10 routed near noisy

electrical signals (coils, spark plug lead, plug
connector).

3. Engine Wiring Harness Related

“32 Pin” (MSE 1.1) Plastic-Cased ECU:

a. Pin circuits 9 and/or 10 wiring or connectors.
b. Shielding for pin circuits 9 and/or 10 damaged

or not properly grounded.

c. Poor or improper grounds in system (battery,

ECU, oxygen sensor, shielding, fuel pump,
ignition output).

d. Pin circuits 9 and/or 10 routed near noisy

electrical signals (coils, spark plug lead, plug
connector).

4. ECU/Harness Related
a. ECU-to-harness connection problem.

5. Ignition System Related
a. Non-resistor spark plug(s) used.

Code: 22
Source: Throttle Position Sensor (TPS)
Explanation: Unrecognizable signal is being sent

from sensor (too high, too low,
inconsistent).

Expected Engine
Response: A “limp-home” operating mode

occurs, with an overall decrease in
operating performance and efficiency.
Fuel delivery is based upon the
oxygen sensor and five mapped
values only. Rich running (black
smoke) will occur until “closed loop”
operation is initiated. A stumble or
misfire on hard acceleration and/or
erratic operation may be exhibited.

Possible Causes:

1. TPS Sensor Related
a. Sensor connector or wiring.
b. Sensor output affected or disrupted by dirt,

grease, oil, wear, or breather tube position
(must be to side opposite the TPS).

c. Sensor loose on throttle body manifold.

2. Throttle Body Related
a. Throttle shaft or bearings worn/damaged.

3. Engine Wiring Harness Related

“24 Pin” (MSE 1.0) Plastic-Cased ECU:

a. Pin circuits 4, 8, and/or 14 damaged (wiring,

connectors).

b. Pin circuits 4, 8, and/or 14 routed near noisy

electrical signal (coils, alternator).

c. Intermittent 5 volt source from ECU (pin

circuit 14).

3. Engine Wiring Harness Related

“32 Pin” (MSE 1.1) Plastic-Cased ECU:

a. Pin circuits 4, 8, and/or 18 damaged (wiring,

connectors).

b. Pin circuits 4, 8, and/or 18 routed near noisy

electrical signal (coils, alternator).

c. Intermittent 5 volt source from ECU (pin

circuit 18).

4. ECU/Harness Related
a. ECU-to-harness connection problem.

5B

5B.33