Kohler CH621, CH23, CH670, CH680, CH25 Service Manual

CH18-CH25, CH620-CH730, CH740, CH750

Service Manual

IMPORTANT: Read all safety precautions and instructions carefully before operating equipment. Refer to operating

instruction of equipment that this engine powers.

Ensure engine is stopped and level before performing any maintenance or service.

2 Safety
3 Maintenance

5 Specications
15 Tools and Aids
18 Troubleshooting
22 Air Cleaner/Intake
23 Fuel System
29 Governor System
31 Lubrication System
33 Electrical System
49 Starter System
58 Clutch
60 Disassembly/Inspection and Service
75 Reassembly

124 690 06 Rev. J KohlerEngines.com

Safety

SAFETY PRECAUTIONS

WARNING: A hazard that could result in death, serious injury, or substantial property damage.

CAUTION: A hazard that could result in minor personal injury or property damage.

NOTE: is used to notify people of important installation, operation, or maintenance information.

WARNING

Explosive Fuel can cause
res and severe burns.

Do not ll fuel tank while
engine is hot or running.

Gasoline is extremely ammable
and its vapors can explode if
ignited. Store gasoline only in
approved containers, in well
ventilated, unoccupied buildings,
away from sparks or ames.
Spilled fuel could ignite if it comes
in contact with hot parts or sparks
from ignition. Never use gasoline
as a cleaning agent.

WARNING

Rotating Parts can cause
severe injury.

Stay away while engine
is in operation.

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

WARNING

Carbon Monoxide can
cause severe nausea,
fainting or death.

Avoid inhaling exhaust
fumes.

Engine exhaust gases contain
poisonous carbon monoxide.
Carbon monoxide is odorless,
colorless, and can cause death if
inhaled.

Accidental Starts can
cause severe injury or
death.

Disconnect and ground
spark plug lead(s) before
servicing.

Before working on engine or
equipment, disable engine as
follows: 1) Disconnect spark plug
lead(s). 2) Disconnect negative (–)
battery cable from battery.

Hot Parts can cause
severe burns.

Do not touch engine
while operating or just
after stopping.

Never operate engine with heat
shields or guards removed.

Cleaning Solvents can
cause severe injury or
death.

Use only in well
ventilated areas away
from ignition sources.

Carburetor cleaners and solvents
are extremely ammable. Follow
cleaner manufacturer’s warnings
and instructions on its proper and
safe use. Never use gasoline as a
cleaning agent.

WARNING

WARNING

WARNING

Electrical Shock can
cause injury.

Do not touch wires while
engine is running.

Damaging Crankshaft
and Flywheel can cause
personal injury.

Using improper procedures can
lead to broken fragments. Broken
fragments could be thrown from
engine. Always observe and use
precautions and procedures when
installing ywheel.

Failure to utilize or
reassemble debris
screen as designed could
result in debris screen
failure and serious
personal injury.

Uncoiling Spring can
cause severe injury.

Wear safety goggles or
face protection when
servicing retractable
starter.

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
for relieving spring tension.

CAUTION

CAUTION

CAUTION

WARNING

2

24 690 06 Rev. JKohlerEngines.com

Maintenance

MAINTENANCE INSTRUCTIONS

WARNING

Accidental Starts can cause severe injury or
death.

Disconnect and ground spark plug lead(s)
before servicing.

Normal maintenance, replacement or repair of emission control devices and systems may be performed by any repair
establishment or individual; however, warranty repairs must be performed by a Kohler authorized dealer.

MAINTENANCE SCHEDULE

Weekly

● Check heavy-duty air cleaner element. Air Cleaner/Intake

Every 25 Hours or Annually¹

● Service/replace low-prole precleaner. Air Cleaner/Intake

Every 100 Hours or Annually¹

● Replace low-prole air cleaner element. Air Cleaner/Intake

● Change oil. Lubrication System/Clutch

● Remove cooling shrouds and clean cooling areas. Air Cleaner/Intake

● Check oil cooler ns, clean as necessary (if equipped). Lubrication System

Before working on engine or equipment, disable engine as
follows: 1) Disconnect spark plug lead(s). 2) Disconnect
negative (–) battery cable from battery.

Every 200 Hours

● Change oil lter. Lubrication System

● Replace fuel lter.

Every 250 Hours¹

● Replace heavy-duty air cleaner element and check inner element. Air Cleaner/Intake

Every 500 Hours¹

● Replace heavy-duty inner air cleaner element. Air Cleaner/Intake

● Replace spark plugs and set gap. Electrical System

Every 500 Hours

2

● Have crankshaft spline lubricated.

1

Perform these procedures more frequently under severe, dusty, dirty conditions.

2

Have a Kohler authorized dealer perform this service.

REPAIRS/SERVICE PARTS

Kohler genuine service parts can be purchased from Kohler authorized dealers. To nd a local Kohler authorized
dealer visit KohlerEngines.com or call 1-800-544-2444 (U.S. and Canada).

324 690 06 Rev. J KohlerEngines.com

Maintenance

OIL RECOMMENDATIONS

We recommend use of Kohler oils for best performance.
Other high-quality detergent oils (including synthetic)
of API (American Petroleum Institute) service class SJ
or higher are acceptable. Select viscosity based on
air temperature at time of operation as shown in table
below.

FUEL RECOMMENDATIONS

WARNING

Explosive Fuel can cause res and severe
burns.

Do not ll fuel tank while engine is hot or
running.

Gasoline is extremely ammable and its vapors can
explode if ignited. Store gasoline only in approved
containers, in well ventilated, unoccupied buildings,
away from sparks or ames. Spilled fuel could ignite
if it comes in contact with hot parts or sparks from
ignition. Never use gasoline as a cleaning agent.

STORAGE

If engine will be out of service for 2 months or more
follow procedure below.

1. Add Kohler PRO Series fuel treatment or equivalent
to fuel tank. Run engine 2-3 minutes to get stabilized
fuel into fuel system (failures due to untreated fuel
are not warrantable).

2. Change oil while engine is still warm from operation.
Remove spark plug(s) and pour about 1 oz. of
engine oil into cylinder(s). Replace spark plug(s) and
crank engine slowly to distribute oil.

3. Disconnect negative (-) battery cable.

4. Store engine in a clean, dry place.

NOTE: E15, E20 and E85 are NOT approved and

should NOT be used; effects of old, stale or
contaminated fuel are not warrantable.

Fuel must meet these requirements:

● Clean, fresh, unleaded gasoline.

● Octane rating of 87 (R+M)/2 or higher.

● Research Octane Number (RON) 90 octane minimum.

● Gasoline up to 10% ethyl alcohol, 90% unleaded is
acceptable.

● Methyl Tertiary Butyl Ether (MTBE) and unleaded
gasoline blend (max 15% MTBE by volume) are
approved.

● Do not add oil to gasoline.

● Do not overll fuel tank.

● Do not use gasoline older than 30 days.

4 24 690 06 Rev. JKohlerEngines.com

Engine Dimensions with Low-Prole Air Cleaner

Specications

Dimensions in millimeters.

Inch equivalents shown in [ ].

524 690 06 Rev. J KohlerEngines.com

Specications

135.00

HOLE “A”

514.05

285.90

Engine Dimensions with Heavy-Duty Air Cleaner

[5.315]

AIR FILTER RAIN

CAP REMOVAL

424.61

[16.717]

93.33
[3.674]

304.48

[11.987]

272.17

[10.715]

AIR FILTER COVER

ASSEMBLY REMOVAL

130.00
[5.118]

Dimensions in millimeters.

Inch equivalents shown in [ ].

[11.256]

50.85

[2.002]

OIL FILL

LOCATION

PULSE

FUEL PUMP

CRANKSHAFT

15.70

[.618]
OIL FILTER
REMOVAL

124.34
[4.895]

MOUNTING

92.10

[3.626]

184.20
[7.252]

ENGINE

CRANKSHAFT

414.17

[16.306]

SAFETY AIR FILTER

ELEMENT REMOVAL

SPARK PLUG

SOLENOID

SHIFT STARTER

15.58
[.613]

526.49

[20.728]
PRIMARY AIR FILTER
ELEMENT REMOVAL

301.36

[11.864]

LIFT STRAP

30˚

ENGINE MOUNTING SURFACE

42.26

[1.664]

115.74
[4.557]

[20.238]

30˚

3/8-16 UNC 2B (INCH)

17.0 [.669]
Ø 165.1 [6.50]B.C.

7/16-14 UNC 2B (INCH)

21.0 [.827]
Ø 196.85 [7.75]B.C.

LIFT STRAP

440.88

[17.357]

626.92

[24.682]

155.58
[6.125]

1/4 IN. SQ KEYWAY

Ø 25.56
[1.125]

7/16-20 UNF 2B (INCH)

38.10 (1.500)

2X OIL DRAIN PLUG

3/8 NPT (INCH)

89.00

[3.504]

MOUNTING HOLE “A”

6 24 690 06 Rev. JKohlerEngines.com

OIL DIPSTICK

70.52

[2.776]

100.00
[3.937]

89.00

[3.504]

ENGINE

MOUNTING

SURFACE

54.00

[2.126]

1/4 IN. SQ KEYWAY

3/8-16 UNC 2B

19.05 [.750]

Specications

ENGINE IDENTIFICATION NUMBERS

Kohler engine identication numbers (model, specication and serial) should be referenced for efcient repair,
ordering correct parts, and engine replacement.

Model .....................CH620

Command Engine

Horizontal Shaft

Numerical Designation

Specication ...............CH620-0001

Serial .....................4323500328

Year Manufactured Code Factory Code

Code Year
43 2013
44 2014
45 2015

GENERAL SPECIFICATIONS

Bore 77 mm

3,6

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

(3.03 in.)

CH22/CH23/

CH6207/
CH6407/

CH670/CH680

80 mm

(3.15 in.)

CH25/

CH730/

CH740

83 mm (3.27 in.)

CH750

Stroke 67 mm (2.64 in.) 69 mm

(2.7 in.)

Displacement 624 cc

(38 cu. in.)

674 cc

(41 cu. in.)

725 cc

(44 cu. in.)

747 cc

(46 cu. in.)
Oil Capacity (rell) 1.6-1.8 L (1.7-1.9 U.S. qt.)
Maximum Angle of Operation (@ full oil level)

TORQUE SPECIFICATIONS

3,5

4

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

25°

CH25/

CH730/

CH740

CH750

Blower Housing and Sheet Metal

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

4.0 N·m (35 in. lb.) into used holes

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

7.3 N·m (65 in. lb.) into used holes

Carburetor and Intake Manifold

Intake Manifold Mounting Fastener (torque in 2
increments)

rst to 7.4 N·m (66 in. lb.)

nally to 9.9 N·m (88 in. lb.)
M6 Mounting Screw 6.2-7.3 N·m (55-65 in. lb.)
Adapter (for Heavy-Duty Air Cleaner) Mounting

7.3 N·m (65 in. lb.)

Fastener

Closure Plate

Fastener 24.4 N·m (216 in. lb.)

3

Values are in Metric units. Values in parentheses are English equivalents.

4

Exceeding maximum angle of operation may cause engine damage from insufcient lubrication.

5

Lubricate threads with engine oil prior to assembly.

6

Any and all horsepower (hp) references by Kohler are Certied Power Ratings and per SAE J1940 & J1995 hp

standards. Details on Certied Power Ratings can be found at KohlerEngines.com.

7

CH620/CH640 engines changed from 624cc to 674cc; displacement can be conrmed on engine nameplate.

724 690 06 Rev. J KohlerEngines.com

Specications

TORQUE SPECIFICATIONS

3,5

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

Connecting Rod

Cap Fastener (torque in increments)
8 mm straight shank
8 mm step-down
6 mm straight shank

22.7 N·m (200 in. lb.)

14.7 N·m (130 in. lb.)

11.3 N·m (100 in. lb.)

Crankcase

Breather Cover Fastener 7.3 N·m (65 in. lb.)
Oil Drain Plug 13.6 N·m (10 ft. lb.)

Cylinder Head

Fastener (torque in 2 increments)
Nut rst to 16.9 N·m (150 in. lb.)

nally to 35.5 N·m (315 in. lb.)

Bolt (torque in 2 increments) rst to 22.6 N·m (200 in. lb.)

nally to 41.8 N·m (370 in. lb.)

Rocker Arm Screw 18.1 N·m (160 in. lb.)

Flywheel

Fan Fastener 9.9 N·m (88 in. lb.)
Flywheel Retaining Screw 66.4 N·m (49 ft. lb.)

CH750

Fuel Pump-Pulse

Fastener 2.3 N·m (20 in. lb.)

Governor

Lever Nut 6.8 N·m (60 in. lb.)

Ignition

Spark Plug 27 N·m (20 ft. lb.)
Module Fastener 4.0-6.2 N·m (35-55 in. lb.)
Rectier-Regulator Fastener 1.4 N·m (12.6 in. lb.)

Mufer

Retaining Nut 24.4 N·m (216 in. lb.)

Oil Cooler

Adapter Nipple 27 N·m (20 ft. lb.)

Oil Sentry

™

Pressure Switch 4.5 N·m (40 in. lb.)

Solenoid (Starter)

Mounting Hardware
Nippondenso Starter
Delco-Remy Starter

6.0-9.0 N·m (53-79 in. lb.)

4.0-6.0 N·m (35-53 in. lb.)

Nut, Positive (+) Brush Lead
Nippondenso Starter
Delco-Remy Starter

8.0-12.0 N·m (71-106 in. lb.)

8.0-11.0 N·m (71-97 in. lb.)

3

Values are in Metric units. Values in parentheses are English equivalents.

5

Lubricate threads with engine oil prior to assembly.

8 24 690 06 Rev. JKohlerEngines.com

Specications

TORQUE SPECIFICATIONS

3,5

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

Speed Control Bracket

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

7.3 N·m (65 in. lb.) into used holes

Starter Assembly

Thru Bolt
Inertia Drive
Nippondenso Solenoid Shift
Delco-Remy Solenoid Shift

4.5-5.7 N·m (40-50 in. lb.)

4.5-7.5 N·m (40-84 in. lb.)

5.6-9.0 N·m (49-79 in. lb.)
Mounting Screw 15.3 N·m (135 in. lb.)
Brush Holder Mounting Screw 2.5-3.3 N·m (22-29 in. lb.)

Stator

Mounting Screw 6.2 N·m (55 in. lb.)

Valve Cover

Gasket Style Cover Fastener 3.4 N·m (30 in. lb.)
Black O-Ring Style Cover Fastener

w/Shoulder Screws
w/Flange Screws and Spacers

5.6 N·m (50 in. lb.)

9.9 N·m (88 in. lb.)

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

CH750

CLEARANCE SPECIFICATIONS

3

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

Camshaft

End Play (w/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
Max. Wear Limit

20.000/20.025 mm (0.7874/0.7884 in.)

20.038 mm (0.7889 in.)

Bearing Surface O.D.
New
Max. Wear Limit

19.962/19.975 mm (0.7859/0.7864 in.)

19.959 mm (0.7858 in.)

Connecting Rod

Connecting Rod-to-Crankpin Running Clearance
New
Max. Wear Limit

0.030/0.055 mm (0.0012/0.0022 in.)

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
Max. Wear Limit

17.015/17.023 mm (0.6699/0.6702 in.)

17.036 mm (0.6707 in.)

CH750

3

Values are in Metric units. Values in parentheses are English equivalents.

5

Lubricate threads with engine oil prior to assembly.

924 690 06 Rev. J KohlerEngines.com

Specications

CLEARANCE SPECIFICATIONS

3

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

Crankcase

Governor Cross Shaft Bore I.D.
6 mm Shaft
New
Max. Wear Limit

6.025/6.050 mm (0.2372/0.2382 in.)

6.063 mm (0.2387 in.)
8 mm Shaft
New
Max. Wear Limit

8.025/8.075 mm (0.3159/0.3179 in.)

8.088 mm (0.3184 in.)

Crankshaft

End Play (free) 0.070/0.590 mm (0.0028/0.0230 in.)
End Play (w/thrust bearing components) 0.070/1.190 mm (0.0028/0.0468 in.)
Except CH25 Engines Below Serial No. 2403500008 0.050/0.750 mm (0.0020/0.0295 in.)
Bore (in crankcase)

New
Max. Wear Limit

40.965/41.003 mm (1.6128/1.6143 in.)

41.016 mm (1.6148 in.)

Crankshaft to Sleeve Bearing (crankcase)
Running Clearance-New 0.03/0.09 mm (0.0012/0.0035 in.)

Bore (in closure plate)
New 40.987/40.974 mm (1.6136/1.6131 in.)

Crankshaft Bore (in closure plate)-to-Crankshaft
Running Clearance-New 0.039/0.074 mm (0.0015/0.0029 in.)

Flywheel End Main Bearing Journal
O.D. - New
O.D. - Max. Wear Limit
Max. Taper
Max. Out-of-Round

40.913/40.935 mm (1.6107/1.6116 in.)

40.84 mm (1.608 in.)

0.022 mm (0.0009 in.)

0.025 mm (0.0010 in.)
Closure Plate End Main Bearing Journal

O.D. - New
O.D. - Max. Wear Limit
Max. Taper
Max. Out-of-Round

40.913/40.935 mm (1.6107/1.6116 in.)

40.84 mm (1.608 in.)

0.022 mm (0.0009 in.)

0.025 mm (0.0010 in.)
Connecting Rod Journal

O.D. - New
O.D. - Max. Wear Limit
Max. Taper
Max. Out-of-Round

35.955/35.973 mm (1.4156/1.4163 in.)

35.94 mm (1.415 in.)

0.018 mm (0.0007 in.)

0.025 mm (0.0010 in.)
T.I.R.

PTO End, Crank in Engine
Entire Crank, in V-Blocks

0.279 mm (0.0110 in.)

0.10 mm (0.0039 in.)

CH750

Cylinder Bore

Bore I.D.
New 77.000/

Max. Wear Limit 77.063 mm

Max. Out-of-Round 0.12 mm (0.0047 in.)
Max. Taper 0.05 mm (0.0020 in.)

Cylinder Head

Max. Out-of-Flatness 0.076 mm (0.003 in.) 0.1 mm (0.004 in.)

3

Values are in Metric units. Values in parentheses are English equivalents.

10 24 690 06 Rev. JKohlerEngines.com

77.025 mm
(3.0315/

3.0325 in.)

(3.0340 in.)

80.000/

80.025 mm
(3.1496/

3.1506 in.)

80.065 mm

(3.1522 in.)

82.988/83.013 mm
(3.2672/3.2682 in.)

83.051 mm
(3.2697 in.)

Specications

CLEARANCE SPECIFICATIONS

3

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

Governor

Governor Cross Shaft-to-Crankcase
Running Clearance
6 mm Shaft
8 mm Shaft

0.013/0.075 mm (0.0005/0.0030 in.)

0.025/0.126 mm (0.0009/0.0049 in.)

Cross Shaft O.D.
6 mm Shaft
New
Max. Wear Limit

5.975/6.012 mm (0.2352/0.2367 in.)

5.962 mm (0.2347 in.)
8 mm Shaft
New
Max. Wear Limit

Governor Gear Shaft-to-Governor Gear

7.949/8.000 mm (0.3129/0.3149 in.)

7.936 mm (0.3124 in.)

0.015/0.140 mm (0.0006/0.0055 in.)

Running Clearance
Gear Shaft O.D.

New
Max. Wear Limit

5.990/6.000 mm (0.2358/0.2362 in.)

5.977 mm (0.2353 in.)

Ignition

Spark Plug Gap 0.76 mm (0.030 in.)
Module Air Gap 0.28/0.33 mm (0.011/0.013 in.)

CH750

Piston, Piston Rings, and Piston Pin

Piston Style A
Piston-to-Piston Pin Running Clearance 0.006/0.017 mm (0.0002/0.0007 in.)
Pin Bore I.D.

New
Max. Wear Limit

17.006/17.012 mm (0.6695/0.6698 in.)

17.025 mm (0.6703 in.)

Pin O.D.
New
Max. Wear Limit

Top Compression Ring-to-Groove Side Clearance 0.040/

0.080 mm
(0.0016/

0.0031 in.)

Middle Compression Ring-to-Groove Side Clearance 0.040/

0.080 mm
(0.0016/

0.0031 in.)

Oil Control Ring-to-Groove Side Clearance 0.060/

0.202 mm
(0.0024/

0.0080 in.)

16.995/17.000 mm (0.6691/0.6693 in.)

16.994 mm (0.6691 in.)

0.030/

0.076 mm

0.025/0.048 mm

(0.0010/0.0019 in.)

(0.0012/

0.0030 in.)

0.030/

0.076 mm

0.015/0.037 mm

(0.0006/0.0015 in.)

(0.0012/

0.0030 in.)

0.046/

0.196 mm

0.026/0.176 mm

(0.0010/0.0070 in.)

(0.0018/

0.0077 in.)

Top and Middle Compression Ring End Gap
New Bore 0.25/

0.45 mm
(0.0098/

0.0177 in.)

Used Bore (Max) 0.77 mm

(0.030 in.)

0.18/

0.46 mm
(0.0071/

0.0181 in.)

0.80 mm

(0.0315 in.)

0.25/0.56 mm

(0.0100/0.0224 in.)

0.94 mm (0.037 in.)

3

Values are in Metric units. Values in parentheses are English equivalents.

1124 690 06 Rev. J KohlerEngines.com

Specications

CLEARANCE SPECIFICATIONS

3

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

CH750

Piston, Piston Rings, and Piston Pin (Style A continued)
Thrust Face O.D.

New 76.943/

Max. Wear Limit 76.816 mm

Piston Thrust Face-to-Cylinder Bore

8

8

Running

76.961 mm
(3.0292/

3.0299 in.)

(3.0242 in.)

79.943/

79.961 mm
(3.1473/

3.1480 in.)

79.816 mm

(3.1423 in.)

82.949/82.967 mm
(3.2656/3.2664 in.)

82.822 mm (3.2606 in.)

Clearance
New 0.039/0.082 mm (0.0015/0.0032 in.)

Piston Style B
Piston-to-Piston Pin Running Clearance 0.006/0.017 mm (0.0002/0.0007 in.)
Pin Bore I.D.

New
Max. Wear Limit

17.006/17.012 mm (0.6695/0.6698 in.)

17.025 mm (0.6703 in.)

Pin O.D.
New
Max. Wear Limit

16.995/17.000 mm (0.6691/0.6693 in.)

16.994 mm (0.6691 in.)
Top Compression Ring-to-Groove Side Clearance 0.030/0.070 mm (0.001/0.0026 in.)
Middle Compression Ring-to-Groove Side Clearance 0.030/0.070 mm (0.001/0.0026 in.)
Oil Control Ring-to-Groove Side Clearance 0.060/0.190 mm (0.0022/0.0073 in.)

Top Compression Ring End Gap
New Bore 0.100/

0.279 mm

0.189/0.277 mm

(0.0074/0.0109 in.)

(0.0039/

0.0110 in.)

Used Bore (Max) 0.490 mm

0.531 mm (0.0209 in.)

(0.0192 in.)

Middle Compression Ring End Gap
New Bore 1.400/

1.679 mm

1.519/1.797 mm

(0.0598/0.0708 in.)

(0.0551/

0.0661 in.)

Used Bore (Max) 1.941 mm

2.051 mm (0.0808 in.)

(0.0764 in.)

Thrust Face O.D.
New 79.966 mm

(3.1483 in.)

Max. Wear Limit 79.821 mm

(3.1426 in.)

82.978 mm (3.2668 in.)

9

82.833 mm (3.2611 in.)

9

Piston Thrust Face-to-Cylinder Bore Running
Clearance
New

0.025/

0.068 mm
(0.0010/

0.0027 in.)

0.019/0.062 mm

(0.0007/0.0024 in.)

9

8

8

8

3

Values are in Metric units. Values in parentheses are English equivalents.

8

Measure 6 mm (0.2362 in.) above bottom of piston skirt at right angles to piston pin.

9

Measure 13 mm (0.5118 in.) above bottom of piston skirt at right angles to piston pin.

12 24 690 06 Rev. JKohlerEngines.com

Specications

CLEARANCE SPECIFICATIONS

3

CH18/CH20/

CH22/

CH620/CH621/

CH640/CH641

CH22/CH23/

CH620/
CH640/

CH670/CH680

CH25/

CH730/

CH740

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
Max. Wear Limit

7.038/7.058 mm (0.2771/0.2779 in.)

7.134 mm (0.2809 in.)

Exhaust Valve Guide I.D.
New
Max. Wear Limit

7.038/7.058 mm (0.2771/0.2779 in.)

7.159 mm (0.2819 in.)

Valve Guide Reamer Size
Standard

0.25 mm O.S

7.048 mm (0.2775 in.)

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°

CH750

3

Values are in Metric units. Values in parentheses are English equivalents.

1324 690 06 Rev. J KohlerEngines.com

Specications

GENERAL TORQUE VALUES

English Fastener Torque Recommendations for Standard Applications

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

Size Grade 2 Grade 5 Grade 8

Tightening Torque: N·m (in. lb.) ± 20%

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) — — —

Tightening Torque: N·m (ft. lb.) ± 20%

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) 142.5 (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) —

5/8-11 149.5 (110) 244.1 (180) 352.6 (260) —

5/8-18 189.8 (140) 311.9 (230) 447.5 (330) —

3/4-10 199.3 (147) 332.2 (245) 474.6 (350) —

3/4-16 271.2 (200) 440.7 (325) 637.3 (470) —

Grade 2 or 5 Fasteners

Into Aluminum

Metric Fastener Torque Recommendations for Standard Applications

Size

4.8

5.8

Tightening Torque: N·m (in. lb.) ± 10%

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)

Tightening Torque: N·m (ft. lb.) ± 10%

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 (56) 131.5 (97) 184.4 (136) 219.7 (162) 94.9 (70)

14 24 690 06 Rev. JKohlerEngines.com

Property Class

8.8

10.9 12.9

Torque Conversions

N·m = in. lb. x 0.113 in. lb. = N·m x 8.85

N·m = ft. lb. x 1.356 ft. lb. = N·m x 0.737

Noncritical

Fasteners

Into Aluminum

Tools and Aids

Certain quality tools are designed to help you perform specic disassembly, repair, and reassembly procedures. By
using these tools, 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 a list of tools and their source.

SEPARATE TOOL SUPPLIERS

Kohler Tools
Contact your local Kohler source of
supply.

TOOLS

Description Source/Part No.

Alcohol Content Tester

For testing alcohol content (%) in reformulated/oxygenated fuels.

Camshaft Endplay Plate

For checking camshaft endplay.

Camshaft Seal Protector (Aegis)

For protecting seal during camshaft installation.

Cylinder Leakdown Tester

For checking combustion retention and if cylinder, piston, rings, or valves are worn.
Individual component available:
Adapter 12 mm x 14 mm (Required for leakdown test on XT-6 engines)

Dealer Tool Kit (Domestic)

Complete kit of Kohler required tools.
Components of 25 761 39-S
Ignition System Tester
Cylinder Leakdown Tester
Oil Pressure Test Kit
Rectier-Regulator Tester (120 V AC/60Hz)

Dealer Tool Kit (International)

Complete kit of Kohler required tools.
Components of 25 761 42-S
Ignition System Tester
Cylinder Leakdown Tester
Oil Pressure Test Kit
Rectier-Regulator Tester (240 V AC/50Hz)

Digital Vacuum/Pressure Tester

For checking crankcase vacuum.
Individual component available:
Rubber Adapter Plug

Electronic Fuel Injection (EFI) Diagnostic Software

For Laptop or Desktop PC.

EFI Service Kit

For troubleshooting and setting up an EFI engine.
Components of 24 761 01-S
Fuel Pressure Tester
Noid Light
90° Adapter
In-line "T" Fitting
Code Plug, Red Wire
Code Plug, Blue Wire
Shrader Valve Adapter Hose

Flywheel Puller

For properly removing ywheel from engine.

SE Tools
415 Howard St.
Lapeer, MI 48446
Phone [phone]
Toll Free 800-664-2981
Fax [phone]

Design Technology Inc.
768 Burr Oak Drive
Westmont, IL 60559
Phone [phone]
Fax [phone]

Kohler 25 455 11-S

SE Tools KLR-82405

SE Tools KLR-82417

Kohler 25 761 05-S

Design Technology Inc.

DTI-731-03

Kohler 25 761 39-S

Kohler 25 455 01-S
Kohler 25 761 05-S
Kohler 25 761 06-S
Kohler 25 761 20-S

Kohler 25 761 42-S

Kohler 25 455 01-S
Kohler 25 761 05-S
Kohler 25 761 06-S
Kohler 25 761 41-S

Design Technology Inc.

DTI-721-01

Design Technology Inc.

DTI-721-10

Kohler 25 761 23-S

Kohler 24 761 01-S

Design Technology Inc.

DTI-019
DTI-021
DTI-023
DTI-035
DTI-027
DTI-029
DTI-037

SE Tools KLR-82408

1524 690 06 Rev. J KohlerEngines.com

Tools and Aids

TOOLS

Description Source/Part No.

Hydraulic Valve Lifter Tool

For removing and installing hydraulic lifters.

Ignition System Tester

For testing output on all systems, including CD.

Inductive Tachometer (Digital)

For checking operating speed (RPM) of an engine.

Offset Wrench (K and M Series)

For removing and reinstalling cylinder barrel retaining nuts.

Oil Pressure Test Kit

For testing/verifying oil pressure on pressure lubricated engines.

Rectier-Regulator Tester (120 volt current)
Rectier-Regulator Tester (240 volt current)

For testing rectier-regulators.
Components of 25 761 20-S and 25 761 41-S
CS-PRO Regulator Test Harness
Special Regulator Test Harness with Diode

Spark Advance Module (SAM) Tester

For testing SAM (ASAM and DSAM) on engines with SMART-SPARK

.

™

Starter Servicing Kit (All Starters)

For removing and reinstalling drive retaining rings and brushes.
Individual component available:
Starter Brush Holding Tool (Solenoid Shift)

Triad/OHC Timing Tool Set

For holding cam gears and crankshaft in timed position while installing timing belt.

Valve Guide Reamer (K and M Series)

For properly sizing valve guides after installation.

Valve Guide Reamer O.S. (Command Series)

For reaming worn valve guides to accept replacement oversize valves. Can be used
in low-speed drill press or with handle below for hand reaming.

Reamer Handle

For hand reaming using Kohler 25 455 12-S reamer.

Kohler 25 761 38-S

Kohler 25 455 01-S

Design Technology Inc.

DTI-110

Kohler 52 455 04-S

Kohler 25 761 06-S

Kohler 25 761 20-S
Kohler 25 761 41-S

Design Technology Inc.

DTI-031
DTI-033

Kohler 25 761 40-S

SE Tools KLR-82411

SE Tools KLR-82416

Kohler 28 761 01-S

Design Technology Inc.

DTI-K828

Kohler 25 455 12-S

Design Technology Inc.

DTI-K830

AIDS

Description Source/Part No.

Camshaft Lubricant (Valspar ZZ613) Kohler 25 357 14-S
Dielectric Grease (GE/Novaguard G661) Kohler 25 357 11-S
Dielectric Grease Loctite

®

51360

Kohler Electric Starter Drive Lubricant (Inertia Drive) Kohler 52 357 01-S
Kohler Electric Starter Drive Lubricant (Solenoid Shift) Kohler 52 357 02-S
RTV Silicone Sealant

Loctite
Only oxime-based, oil resistant RTV sealants, such as those listed, are approved

®

5900® Heavy Body in 4 oz. aerosol dispenser.

for use. Loctite® Nos. 5900® or 5910® are recommended for best sealing
characteristics.

Kohler 25 597 07-S

Loctite® 5910

®

Loctite® Ultra Black 598™

Loctite® Ultra Blue 587™

Loctite® Ultra Copper 5920™

Spline Drive Lubricant Kohler 25 357 12-S

16 24 690 06 Rev. JKohlerEngines.com

Tools and Aids

FLYWHEEL HOLDING TOOL ROCKER ARM/CRANKSHAFT TOOL

A ywheel holding tool can be made out of an old junk
ywheel ring gear and used in place of a strap wrench.

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

2. Grind off any burrs or sharp edges.

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

A spanner wrench to lift rocker arms or turn 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 rod cap.

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

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

4. Use a at washer with correct I.D. to slip on
capscrew and approximately 1 in. O.D. Assemble
capscrew and washer to joint surface of rod.

1724 690 06 Rev. J KohlerEngines.com

Troubleshooting

TROUBLESHOOTING GUIDE

When troubles occur, be sure to check simple causes which, at rst, 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 and vary by engine specication. Use these to
locate causing factors.

Engine Cranks But Will Not Start

● Battery connected backwards.

● Blown fuse.

● Carburetor solenoid malfunction.

● Choke not closing.

● Clogged fuel line or fuel lter.

● Diode in wiring harness failed in open circuit mode.

● DSAI or DSAM malfunction.

● Empty fuel tank.

● Faulty electronic control unit.

● Faulty ignition coil(s).

● Faulty spark plug(s).

● Fuel pump malfunction-vacuum hose clogged or
leaking.

● Fuel shut-off valve closed.

● Ignition module(s) faulty or improperly gapped.

● Insufcient voltage to electronic control unit.

● Interlock switch is engaged or faulty.

● Key switch or kill switch in OFF position.

● Low oil level.

● Quality of fuel (dirt, water, stale, mixture).

● SMART-SPARKTM malfunction.

● Spark plug lead(s) disconnected.

Engine Starts But Does Not Keep Running

● Faulty carburetor.

● Faulty cylinder head gasket.

● Faulty or misadjusted choke or throttle controls.

● Fuel pump malfunction-vacuum hose clogged or
leaking.

● Intake system leak.

● Loose wires or connections that intermittently ground
ignition kill circuit.

● Quality of fuel (dirt, water, stale, mixture).

● Restricted fuel tank cap vent.

Engine Starts Hard

● Clogged fuel line or fuel lter.

● Engine overheated.

● Faulty ACR mechanism.

● Faulty or misadjusted choke or throttle controls.

● Faulty spark plug(s).

● Flywheel key sheared.

● Fuel pump malfunction-vacuum hose clogged or
leaking.

● Interlock switch is engaged or faulty.

● Loose wires or connections that intermittently ground
ignition kill circuit.

● Low compression.

● Quality of fuel (dirt, water, stale, mixture).

● Weak spark.

Engine Will Not Crank

● Battery is discharged.

● Faulty electric starter or solenoid.

● Faulty key switch or ignition switch.

● Interlock switch is engaged or faulty.

● Loose wires or connections that intermittently ground
ignition kill circuit.

● Pawls not engaging in drive cup.

● Seized internal engine components.

Engine Runs But Misses

● Carburetor adjusted incorrectly.

● Engine overheated.

● Faulty spark plug(s).

● Ignition module(s) faulty or improperly gapped.

● Incorrect crankshaft position sensor air gap.

● Interlock switch is engaged or faulty.

● Loose wires or connections that intermittently ground
ignition kill circuit.

● Quality of fuel (dirt, water, stale, mixture).

● Spark plug lead(s) disconnected.

● Spark plug lead boot loose on plug.

● Spark plug lead loose.

Engine Will Not Idle

● Engine overheated.

● Faulty spark plug(s).

● Idle fuel adjusting needle(s) improperly set.

● Idle speed adjusting screw improperly set.

● Inadequate fuel supply.

● Low compression.

● Quality of fuel (dirt, water, stale, mixture).

● Restricted fuel tank cap vent.

Engine Overheats

● Cooling fan broken.

● Excessive engine load.

● Fan belt failed/off.

● Faulty carburetor.

● High crankcase oil level.

● Lean fuel mixture.

● Low cooling system uid level.

● Low crankcase oil level.

● Radiator, and/or cooling system components clogged,
restricted, or leaking.

● Water pump belt failed/broken.

● Water pump malfunction.

Engine Knocks

● Excessive engine load.

● Hydraulic lifter malfunction.

● Incorrect oil viscosity/type.

● Internal wear or damage.

● Low crankcase oil level.

● Quality of fuel (dirt, water, stale, mixture).

18 24 690 06 Rev. JKohlerEngines.com

Troubleshooting

Engine Loses Power

● Dirty air cleaner element.

● Engine overheated.

● Excessive engine load.

● Restricted exhaust.

● Faulty spark plug(s).

● High crankcase oil level.

● Incorrect governor setting.

● Low battery.

● Low compression.

● Low crankcase oil level.

● Quality of fuel (dirt, water, stale, mixture).

Engine Uses Excessive Amount of Oil

● Loose or improperly torqued fasteners.

● Blown head gasket/overheated.

● Breather reed broken.

● Clogged, broken, or inoperative crankcase breather.

● Crankcase overlled.

● Incorrect oil viscosity/type.

● Worn cylinder bore.

● Worn or broken piston rings.

● Worn valve stems/valve guides.

Oil Leaks from Oil Seals, Gaskets

● Breather reed broken.

● Clogged, broken, or inoperative crankcase breather.

● Loose or improperly torqued fasteners.

● Piston blow by, or leaky valves.

● Restricted exhaust.

EXTERNAL ENGINE INSPECTION

NOTE: It is good practice to drain oil at a location away

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

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

● Check for buildup of dirt and debris on crankcase,
cooling ns, grass screen, and other external surfaces.
Dirt or debris on these areas can cause overheating.

● Check for obvious fuel and oil leaks, and damaged
components. Excessive oil leakage can indicate a
clogged or inoperative breather, worn or damaged
seals or gaskets, or loose fasteners.

● Check air cleaner cover and base for damage or
indications of improper t and seal.

● Check air cleaner element. Look for holes, tears,
cracked or damaged sealing surfaces, or other
damage that could allow unltered air into engine. A
dirty or clogged element could indicate insufcient or
improper maintenance.

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

● Check if oil level is within operating range on dipstick.
If it is above, sniff for gasoline odor.

● Check condition of oil. Drain oil into a container; it
should ow 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 over rich fuel settings, weak ignition,
overextended oil change interval or wrong weight or
type of oil was used.

CLEANING ENGINE

WARNING

Cleaning Solvents can cause severe injury or
death.

Use only in well ventilated areas away from
ignition sources.

Carburetor cleaners and solvents are extremely
ammable. Follow cleaner manufacturer’s warnings
and instructions on its proper and safe use. Never use
gasoline as a cleaning agent.

After inspecting external condition of engine, clean
engine thoroughly before disassembly. Clean individual
components as 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
manufacturer’s instructions and safety precautions
carefully.

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

1924 690 06 Rev. J KohlerEngines.com

Troubleshooting

CRANKCASE VACUUM TEST

WARNING

Carbon Monoxide can cause severe nausea,
fainting or death.

Avoid inhaling exhaust fumes.

Engine exhaust gases contain poisonous carbon
monoxide. Carbon monoxide is odorless, colorless,
and can cause death if inhaled.

A partial vacuum should be present in crankcase when engine is operating. Pressure in 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. Complete instructions are
provided in kits.

To test crankcase vacuum with manometer:

1. Insert rubber stopper into oil ll hole. Be sure pinch
clamp is installed on hose and use tapered adapters
to connect hose between stopper and one
manometer tube. Leave other tube open to
atmosphere. Check that water level in manometer is
at 0 line. Make sure pinch clamp is closed.

2. Start engine and run no-load high speed.

3. Open clamp and note water level in tube.

Level in engine side should be a minimum of

10.2 cm (4 in.) above level in open side.

If level in engine side is less than specied (low/no

vacuum), or level in engine side is lower than level in
open side (pressure), check for conditions in table
below.

4. Close pinch clamp before stopping engine.

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

To test crankcase vacuum with vacuum/pressure gauge:

1. Remove dipstick or oil ll plug/cap.

2. Install adapter into oil ll/dipstick tube opening,

3. Run engine and observe gauge reading.
Analog tester–needle movement to left of 0 is a

Digital tester–depress test button on top of tester.
Crankcase vacuum should be a minimum of 10.2 cm

Rotating Parts can cause severe injury.
Stay away while engine is in operation.

upside down over end of a small diameter dipstick
tube, or directly into engine if a tube is not used.
Insert barbed gauge tting into hole in stopper.

vacuum, and movement to right indicates a pressure.

(4 in.) of water. If reading is below specication, or if
pressure is present, check table below for possible
causes and conclusions.

WARNING

Condition Conclusion

Crankcase breather clogged or inoperative. NOTE: If breather is integral part of valve cover and

cannot be serviced separately, replace valve
cover and recheck pressure.

Disassemble breather, clean parts thoroughly, check
sealing surfaces for atness, reassemble, and recheck
pressure.

Seals and/or gaskets leaking. Loose or improperly torque
fasteners.

Piston blow by or leaky valves (conrm by inspecting
components).

Restricted exhaust. Check exhaust screen/spark arrestor (if equipped). Clean

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

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

or replace as needed. Repair or replace any other
damaged/restricted mufer or exhaust system parts.

20 24 690 06 Rev. JKohlerEngines.com

Troubleshooting

COMPRESSION TEST

For Command Twins:
A compression test is best performed on a warm engine. Clean any dirt or debris away from base of spark plug(s)

before removing them. Be sure choke is off, and throttle is wide open during test. Compression should be at least 160
psi and should not vary more than 15% between cylinders.

All other models:
These engines are equipped with an automatic compression release (ACR) mechanism. It is difcult to obtain an

accurate compression reading because of ACR mechanism. As an alternative, use cylinder leakdown test described
below.

CYLINDER LEAKDOWN TEST

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

Cylinder leakdown tester is a relatively simple, inexpensive leakdown tester for small engines. This tester includes a
quick-connect for attaching adapter hose and a holding tool.

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

2. Remove spark plug(s) and air lter from engine.

3. Rotate crankshaft until piston (of cylinder being tested) is at top dead center (TDC) of compression stroke. Hold

engine in this position while testing. Holding tool supplied with tester can be used if PTO end of crankshaft is
accessible. Lock holding tool onto crankshaft. Install a 3/8 in. breaker bar into hole/slot of holding tool, so it is
perpendicular to both holding tool and crankshaft PTO.

If ywheel end is more accessible, use a breaker bar and socket on ywheel nut/screw to hold it in position. An

assistant may be needed to hold breaker bar during testing. If 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 engine cannot rotate off of
TDC in either direction.

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

5. Turn regulator knob completely counterclockwise.

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

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

8. Connect tester quick-connect to adapter hose. While rmly holding engine at TDC, gradually open tester valve.

Note gauge reading and listen for escaping air at combustion air intake, exhaust outlet, and crankcase breather.

Condition Conclusion

Air escaping from crankcase breather. Ring or cylinder worn.
Air escaping from exhaust system. Defective exhaust valve/improper seating.
Air escaping from intake. 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.

2124 690 06 Rev. J KohlerEngines.com

Air Cleaner/Intake

AIR CLEANER

These systems are CARB/EPA certied and components
should not be altered or modied in any way.

Low-Prole Air Cleaner Components

A

B

C

E

F

H

A Air Cleaner Cover B Air Cleaner Knob
C Wing Nut D Element Cover
E Rubber Seal F Precleaner
G Paper Element H Air Cleaner Base

Heavy-Duty Air Cleaner Components

D

G

NOTE: Operating engine with loose or damaged air

cleaner components could cause premature
wear and failure. Replace all bent or damaged
components.

NOTE: Paper element cannot be blown out with

compressed air.

Low-Prole

Loosen knob and remove air cleaner cover.

Precleaner

1. Remove precleaner from paper element.

2. Replace or wash precleaner in warm water with
detergent. Rinse and allow to air dry.

3. Saturate precleaner with new engine oil; squeeze
out excess oil.

4. Reinstall precleaner over paper element.

Paper Element

1. Clean area around element. Remove wing nut,
element cover, and paper element with precleaner.

2. Separate precleaner from element; service
precleaner and replace paper element.

3. Check condition of rubber seal and replace if
necessary.

4. Install new paper element on base; install precleaner
over paper element; reinstall element cover and
secure with wing nut.

Reinstall air cleaner cover and secure with knob.

M

I

N

J

K

I Air Cleaner Housing J Element

K End Cap L Dust Ejector Valve
M Retaining Clip N Inner Element
O Ejector Area P Inlet Screen
Q

Filter Minder

M

L

P

Q

O

Heavy-Duty

1. Unhook retaining clips and remove end cap(s).

2. Check and clean inlet screen (if equipped).

3. Pull air cleaner element out of housing and replace.
Check condition of inner element; replace when
dirty.

4. Check all parts for wear, cracks, or damage, and that
ejector area is clean.

5. Install new element(s).

6. Reinstall end cap(s) with dust ejector valve/screen
down; secure with retaining clips.

BREATHER TUBE

Ensure sure both ends of breather tube are properly
connected.

AIR COOLING

WARNING

Hot Parts can cause severe burns.
Do not touch engine while operating or just

after stopping.

Never operate engine with heat shields or guards
removed.

Proper cooling is essential. To prevent over heating,
clean screens, cooling ns, and other external surfaces
of engine. Avoid spraying water at wiring harness or any
electrical components. Refer to Maintenance Schedule.

22 24 690 06 Rev. JKohlerEngines.com

Fuel System

Typical carbureted fuel system and related components
include:

● Fuel tank and valve.

● Fuel lines.

● In-line fuel lter.

● Fuel pump.

● Carburetor.

Fuel from tank is moved through in-line lter and fuel
lines by fuel pump. Fuel then enters carburetor oat bowl
and is drawn into carburetor body and mixed with air.
This fuel-air mixture is then burned in engine combustion
chamber.

FUEL RECOMMENDATIONS

Refer to Maintenance.

FUEL LINE

Low permeation fuel line must be installed on carbureted
Kohler Co. engines to maintain EPA and CARB
regulatory compliance.

FUEL PUMP

These engines use either a mechanical pump or a pulse
style fuel pump. Pumping action of pulse style pumps is
created by oscillation of positive and negative pressures
within crankcase. This pressure is transmitted to pulse
pump through rubber hose connected between pump
and crankcase. Pumping action causes diaphragm on
inside of pump to pull fuel in on its downward stroke
and to push it into carburetor on its upward stroke. Two
check valves prevent fuel from going backward through
pump.

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.

Fuel Pump Replacement

Pulse Fuel Pump

NOTE: On most models, pulse line is connected to a

tting on crankcase, while on early models, it is
connected to valve cover.

NOTE: Make sure orientation of new pump is consistent

with removed pump. Internal damage may occur
if installed incorrectly.

To replace pulse pump follow these steps. Note
orientation of pump before removing.

1. Disconnect fuel lines from inlet, outlet, and pulse

ttings on fuel pump.

2. Remove screws and take off pump.

3. Connect pulse line to new fuel pump and make sure

opposite end is properly connected to tting on
crankcase or valve cover.

4. Attach new fuel pump using screws. Torque screws

to 2.3 N·m (20 in. lb.).

5. Reconnect fuel lines to inlet and outlet ttings and

secure with clamps.

Mechanical Pump

Mechanical fuel pump is an integral part of valve cover
assembly and not serviced separately.

1. Disconnect fuel lines from inlet and outlet ttings.

Note orientation.

2. Follow procedure for replacing valve cover. Refer to

Disassembly and Reassembly.

3. Reconnect fuel lines to inlet and outlet ttings and

secure with clamps.

FUEL SYSTEM TESTS

When engine starts hard or turns over but will not start, fuel system might be causing problems. Test fuel system by
performing following test.

1. Check for fuel in combustion chamber.
a. Disconnect and ground spark plug leads.
b. Close choke on carburetor.
c. Crank engine several times.
d. Remove spark plug and check for fuel at tip.

2. Check for fuel ow from tank to fuel pump.

Condition Conclusion

Fuel at tip of spark plug. Fuel is reaching combustion chamber.
No fuel at tip of spark plug. Check fuel ow from fuel tank (step 2).
Fuel ows from fuel line. Check for faulty fuel pump (step 3).

No fuel ow from fuel line. Check fuel tank cap vent, fuel pickup screen, in-line

Fuel line condition. Check for a clogged fuel line. If fuel line is unobstructed,

a. Remove fuel line from inlet tting of fuel pump.
b. Hold line below bottom of tank. Open shut-off

valve (if equipped) and observe ow.

3. Check operation of fuel pump.
a. Remove fuel line from inlet tting of carburetor.
b. Crank engine several times and observe ow.

If fuel pump is working, check for faulty carburetor. Refer
to Carburetor.

lter, shut-off valve, and fuel line. Correct any observed
problem and reconnect line.

check for overlled crankcase and/or oil in pulse line. If
checks don't reveal cause of problem, replace pump.

2324 690 06 Rev. J KohlerEngines.com

Fuel System

CARBURETORS

WARNING

Explosive Fuel can cause res and severe
burns.

Do not ll fuel tank while engine is hot or
running.

Keihin Two-Barrel Carburetor Components

D

E

F

G

B

AF

AE

C

Gasoline is extremely ammable and its vapors can
explode if ignited. Store gasoline only in approved
containers, in well ventilated, unoccupied buildings, away
from sparks or ames. Spilled fuel could ignite if it comes
in contact with hot parts or sparks from ignition. Never use
gasoline as a cleaning agent.

H

AB

AA

I

A

K

U

AC

AD

L

Z

J

T

Q

R

V

X

Carburetor Body

A

Subassembly

F

K

P Sealing Washer Q Float R Pin S Screw T Float Clip

U

Z Choke Dust Cap AA Choke Shaft AB Spring AC Bushing AD Choke Lever

AE Choke Plate AF

Retaining

Washer

O-ring (Fuel

Bowl-Upper)

Float Valve/
Inlet Needle

Y

B

G

L

V

W

Idle Speed

Screw

Slow Jet-

Right Side

O-ring (Fuel

Bowl-Lower)

Main Nozzle-

Right Side

Choke Plate

Screw

M

S

C

H

M Drain Screw N Bowl Screw O Fuel Solenoid

W

Idle Speed

Spring

Slow Jet­Left Side

Main Nozzle-

Left Side

D Screw E Ground Lead

I

X

P

O-ring

(Slow Jet)

Main Jet-

Right Side

N

O

J Fuel Bowl

Y

Main Jet-

Left Side

24

24 690 06 Rev. JKohlerEngines.com

Fuel System

Keihin One-Barrel Carburetor Components

B

D

E

F

G

I

M

N

J

Engines in this series are equipped with Keihin xed
main jet carburetors. CH18-740 engines use a one­barrel carburetor. Most applications use a fuel shut-off
solenoid installed in place of fuel bowl retaining screw,

A

C

O

H

L

K

and also contain an accelerator pump. All carburetors
feature a self-relieving choke. CH750 engines use
a Keihin two-barrel carburetor on a matching intake
manifold.

Troubleshooting Checklist

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

1. Make sure fuel tank is lled with clean, fresh

gasoline.

2. Make sure fuel tank cap vent is not blocked and that

it is operating properly.

3. Make sure fuel is reaching carburetor. This includes

checking fuel shut-off valve, fuel tank lter screen,
in-line fuel lter, fuel lines and fuel pump for
restrictions or faulty components as necessary.

4. Make sure air cleaner base and carburetor are

securely fastened to engine using gaskets in good
condition.

5. Make sure air cleaner element (including precleaner

if equipped) is clean and all air cleaner components
are fastened securely.

6. Make sure ignition system, governor system,

exhaust system, and throttle and choke controls are
operating properly.

S

Q

W

U

V

T

Carburetor Upper

A

C

E Inlet Needle Valve F Clip
G Float Pin H Float Assembly

I

K

M Fuel Shut-off Solenoid N

O

Q Diaphragm R Diaphragm Spring
S O-Ring T Rubber Boot
U Bushing V Return Spring

W Accelerator Pump

Body (Choke)

Body Gasket (Formed

Rubber)

Carburetor Lower

Body (Throttle)

Idle Fuel Adjusting

Needle

Jet (Accelerator Pump

Carburetor only)

B Self-relieving Choke

D Slow Speed Jet

J Main Jet

L Solenoid Seat

P

S

P

Idle Speed Adjusting

Screw

Accelerator Pump

Cover

R

2524 690 06 Rev. J KohlerEngines.com

Fuel System

Troubleshooting-Carburetor Related Causes

Condition Possible Cause Conclusion

Engine starts hard, runs rough, or
stalls at idle speed.

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

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

Fuel leaks from carburetor. Float level is set too high. Separate carburetor air horn from

Low idle fuel mixture (some models)/
speed improperly adjusted.

Clogged air cleaner. Clean or replace air cleaner.
Choke partially closed during

operation.
Low idle fuel mixture is improperly

adjusted.
Float level is set too high. Separate carburetor air horn from

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

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

Leaky, cracked, or damaged oat. Submerge oat to check for leaks.
Low idle fuel mixture is improperly

adjusted.
Float level is set too low. Separate carburetor air horn from

Idle holes plugged; dirt in fuel delivery
channels.

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

Bowl vents plugged. Blow out with compressed air.

Adjust low idle speed tab, then adjust
low idle fuel needle.

Check choke lever/linkage to ensure
choke is operating properly.

Adjust low idle fuel needle (some
models).

carburetor body, adjust oat
according to steps outlined in repair
kit installation instructions.

seat and blow with compressed air.

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

Adjust low idle fuel needle (some
models).

carburetor body, adjust oat
according to steps outlined in repair
kit installation instructions.

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

carburetor body, adjust oat
according to steps outlined in repair
kit installation instructions.

seat and blow with compressed air.

Fuel Shut-Off Solenoid

Most carburetors are equipped with a fuel shut-off solenoid. Solenoid is attached to fuel bowl. Solenoid has a spring­loaded pin that retracts when 12 volts is applied to lead, allowing fuel ow to main jet. When current is removed, pin
extends blocking fuel ow.

Below is a simple test, performed with engine off, that can determine if solenoid is functioning properly.

1. Shut off fuel and remove solenoid from carburetor. When solenoid is loosened and removed, gas will leak out of
carburetor. Have a container ready to catch fuel.

2. Wipe tip of solenoid with a shop towel or blow with compressed air to remove any remaining fuel. Take 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 power source is switched OFF. Connect positive power source lead to red lead of solenoid. Connect
negative power source lead to solenoid body.

4. Turn power source ON and observe pin in center of solenoid. Pin should retract with power ON and return to its
original position with power OFF. Test several times to verify operation.

26

Carburetor bowl gasket leaks. Replace gasket.

24 690 06 Rev. JKohlerEngines.com

Fuel System

Carburetor Circuits

Float

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

Slow and Mid-Range

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

Main (high-speed)

At high speeds/loads engine operates on main circuit.
As a metered amount of air is drawn through air jet,
fuel is drawn through main jet. Air and fuel are mixed
in main nozzles then enters main body of airow where
further mixing of fuel and air occurs. This mixture is then
delivered to combustion chamber. Carburetor has a xed
main circuit; no adjustment is possible.

Carburetor Adjustments

NOTE: Carburetor adjustments should be made only

after engine has warmed up.

Carburetor is designed to deliver correct fuel-to-air
mixture to engine under all operating conditions. Main
fuel jet is calibrated at factory and is not adjustable.
Idle fuel adjusting needles are also set at factory and
normally do not need adjustment.

Low Idle Speed (RPM) Adjustment

NOTE: Actual low idle speed depends on application.

Refer to equipment manufacturer’s
recommendations. Low idle speed for basic
engines is 1200 RPM.

Place throttle control into idle or slow position. Turn low
idle speed adjusting screw in or out to obtain allow idle
speed of 1200 RPM (± 75 RPM).

Governed Idle Speed Adjustment (If equipped)

1. Hold governor lever away from carburetor so throttle

lever is against idle speed (RPM) adjustment screw
of carburetor. Start engine and allow to warm up,
then adjust screw to set approximately 1200 RPM.
Check speed using a tachometer. Turn adjustment
screw (inner) clockwise (in) to increase or
counterclockwise (out) to decrease speed.

2. Release governor lever and check that throttle lever
is in idle position. Turn governed idle adjustment
screw to obtain equipment manufacturer’s
recommended idle speed (1500-1800 RPM). Some
engines have a bendable tab that is used to set this
speed. A pliers should be used to bend this tab to
achieve recommended speed. Governed idle speed
(RPM) is typically 300 RPM (approximate) higher
than low idle speed.

3. Move throttle lever to wide-open/full throttle position
and hold in this position. Turn high speed screw to
obtain intended high speed no-load RPM. Governed
idle speed must be set before making this
adjustment.

Low Idle Fuel Adjustment
Optimum Low Idle Fuel Setting

BB

CC

AA

ED

A Rich B Lean

C Midpoint D Left Side

E Right Side

NOTE: Engines will have xed low idle or limiter caps

on idle fuel adjusting needles. Step 2 can only
be performed within limits allowed by cap. Do
not attempt to remove limiter caps.

1. Place throttle control into idle or slow position. Adjust
low idle speed to 1200 RPM. Follow Low Idle Speed
(RPM) Adjustment.

2. Low idle fuel needle(s) setting: place throttle into idle
or slow position.

a. Turn 1 low idle fuel adjusting needle out

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

b. Repeat procedure on other low idle adjustment

needle (two-barrel carburetor only).

3. Recheck/adjust Low Idle Speed (RPM) to specied
setting.

High Speed (RPM) Adjustment

1. With engine running, move throttle control to fast.

2. Turn inner adjustment screw outward to decrease, or
inward to increase RPM speed. Courage singles
require loosening screws on speed control bracket
and sliding towards carburetor to lower and away
from carburetor to increase speed.

2724 690 06 Rev. J KohlerEngines.com

Fuel System

Carburetor Servicing

WARNING

Accidental Starts can cause severe injury or
death.

Disconnect and ground spark plug lead(s)
before servicing.

Before working on engine or equipment, disable
engine as follows: 1) Disconnect spark plug lead(s). 2)
Disconnect negative (–) battery cable from battery.

NOTE: Main and slow jets are xed and size specic

and can be removed if required. Fixed jets for
high altitudes are available.

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

● Inspect oat for cracks, holes, and missing or
damaged oat tabs. Check oat hinge and shaft for
wear or damage.

● Inspect fuel inlet needle and seat for wear or damage.

● Inspect spring loaded choke plate to make sure it
moves freely on shaft.

1. Perform removal procedures for appropriate air

cleaner and carburetor outlined in Disassembly.

2. Clean exterior surfaces of dirt or foreign material

before disassembling carburetor. Remove bowl
retaining screws, or solenoid assembly on most
single cylinder engines, and carefully separate fuel
bowl from carburetor. Do not damage fuel bowl
O-rings. Transfer any remaining fuel into an
approved container. Save all parts. Fuel can also be
drained prior to bowl removal by loosening/removing
bowl drain screw.

3. Remove oat pin (some carburetors may have a

screw which requires removal), and inlet needle.
Seat for inlet needle is not serviceable and should
not be removed.

4. Clean carburetor bowl and inlet seat areas as

required.

5. Carefully remove main jets from carburetor. For

two-barrel carburetors, note and mark jets by
location for proper reassembly. Main jets may be
size/side specic. After main jets are removed, on
some carburetors, main nozzles can be removed
through bottom of main towers. Note orientation/
direction of nozzles. End with 2 raised shoulders
should be out/down adjacent to main jets. Save
parts for cleaning and reuse.

6. Position of slow jet varies and is removable only on

some styles of carburetors. See correct illustration
for corresponding style of carburetor showing
location. (On two-barrel carburetors, slow jets may
be sized to specic side. Mark or tag jets for proper
reassembly. Note small O-ring on bottom of each
jet.) Save parts for cleaning and reuse unless a jet
kit is also being installed. Clean slow jets using
compressed air. Do not use wire or carburetor
cleaner.

Carburetor is now disassembled for appropriate cleaning
and installation of parts in overhaul kit. See instructions
provided with repair kits for more detailed information.

High Altitude Operation

Engines may require a high altitude carburetor kit to
ensure correct engine operation at altitudes above
1219 meters (4000 ft.). To obtain high altitude kit
information or to nd a Kohler authorized dealer visit
KohlerEngines.com or call1-800-544-2444 (U.S. and
Canada).

This engine should be operated in its original
conguration below 1219 meters (4000 ft.) as damage
may occur if high altitude carburetor kit is installed and
operated below 1219 meters (4000 ft.).

28

24 690 06 Rev. JKohlerEngines.com