Tecumseh V-twin, TVT 691 Technician's Handbook
V-TWIN
TECUMSEH
ENGINE
Small Engine Parts
TABLE OF CONTENTS
CHAPTER 1. GENERAL INFORMATION
CHAPTER 2. AIR CLEANERS
CHAPTER 3. CARBURETORS AND FUEL SYSTEMS
CHAPTER 4. GOVERNORS AND LINKAGE
CHAPTER 5. ELECTRICAL SYSTEMS
CHAPTER 6. IGNITION
CHAPTER 7. INTERNAL ENGINE AND DISASSEMBLY
CHAPTER 8. ENGINE ASSEMBLY
CHAPTER 9. TROUBLESHOOTING AND TESTING
CHAPTER 10. ENGINE SPECIFICATIONS
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retrieval system, without permission in writing from Tecumseh Products Company Training Department
Manager.
Copyright © 2000 by Tecumseh Products Company
i
TABLE OF CONTENTS
GENERAL INFORMATION
Engine Identification ................................................................................................1-1
Interpretation of Engine Identification ......................................................................1-1
Short Blocks ............................................................................................................1-2
Fuels........................................................................................................................1-2
Engine Oil ................................................................................................................1-3
Basic Tune-Up Procedure .......................................................................................1-4
Storage....................................................................................................................1-4
AIR CLEANERS
General Information.................................................................................................2-1
Operation.................................................................................................................2-1
Components ............................................................................................................2-1
Troubleshooting and Testing....................................................................................2-1
Service.....................................................................................................................2-2
(by subject)
Page
CARBURETORS AND FUEL SYSTEMS
General Information.................................................................................................3-1
Float Style Carburetors............................................................................................3-1
Operational Circuits Series 7 Carburetor.................................................................3-1
Testing .....................................................................................................................3-3
Carburetor Disassembly Procedure ........................................................................3-5
Inspection ................................................................................................................3-7
Carburetor Re-Assembly .........................................................................................3-7
Throttle Shaft and Plate...................................................................................3-7
Choke Shaft and Plate.....................................................................................3-8
Fuel Bowl Assembly ........................................................................................3-8
Impulse Fuel Pumps................................................................................................3-9
Impulse Fuel Pump Service...........................................................................3-10
GOVERNORS AND LINKAGE
General Information.................................................................................................4-1
Operation.................................................................................................................4-1
Troubleshooting.......................................................................................................4-1
Engine Speed Adjustments .....................................................................................4-1
Engine Overspeed...........................................................................................4-2
Engine Surging ................................................................................................4-2
Governor Service
Static Adjustment - Governor ..........................................................................4-2
Governor Gear and Shaft Service ...................................................................4-3
Governor Shaft Replacement ..........................................................................4-3
ii
TABLE OF CONTENTS (continued)
Speed Controls and Linkage ...................................................................................4-3
Synchronizing the Carburetors ................................................................................4-4
Choke Synchronization............................................................................................4-5
ELECTRICAL SYSTEMS
General Information.................................................................................................5-1
Operation.................................................................................................................5-1
Converting Alternating Current to Direct Current.....................................................5-2
Components
Battery ............................................................................................................5-2
Wiring..............................................................................................................5-2
Condition.........................................................................................................5-2
Wire Gauge.....................................................................................................5-2
Electrical Terms .......................................................................................................5-3
Basic Checks...........................................................................................................5-3
Charging Circuit.......................................................................................................5-4
3 Amp D.C. 5 Amp A.C. Alternator .........................................................................5-4
Diode Replacement ........................................................................................5-4
Checking the System......................................................................................5-5
16 Amp Alternator System with External Regulator.................................................5-5
Troubleshooting Electrical Charging Circuit Flow Chart ..........................................5-6
Voltage Regulators ..................................................................................................5-7
Fuel Shut-Down Solenoids ......................................................................................5-7
Low Oil Pressure Sensor Testing.............................................................................5-7
Starting Circuit .........................................................................................................5-8
Testing Procedure Starting Circuit ..................................................................5-8
Troubleshooting Electrical Starter Circuit Flow Chart .....................................5-9
Electric Starter Service ..........................................................................................5-10
12 Volt Electric Starter ..................................................................................5-10
Inspection and Repair...................................................................................5-11
Brush Holder.................................................................................................5-12
Brush Replacement ......................................................................................5-12
Page
IGNITION
General Information.................................................................................................6-1
Operation
Solid State Ignition System (CDI) ............................................................................6-1
Components ....................................................................................................6-1
Testing Procedure............................................................................................6-2
Service
Spark Plug Service ..........................................................................................6-3
Conditions Causing Frequent Spark Plug Fouling...........................................6-3
Ignition Timing .........................................................................................................6-3
Service Tips.............................................................................................................6-4
iii
TABLE OF CONTENTS (continued)
INTERNAL ENGINE AND DISASSEMBLY
General Information.................................................................................................7-1
Lubrication Systems ................................................................................................7-1
Disassembly Procedure...........................................................................................7-1
Disassembly of Cylinder Heads...............................................................................7-4
Valves ..............................................................................................................7-5
Valve Guides ...................................................................................................7-5
Valve Springs...................................................................................................7-6
Push Rods .......................................................................................................7-6
Valve Seats......................................................................................................7-6
Internal Engine Component Inspection
Cylinders..........................................................................................................7-7
Pistons.............................................................................................................7-8
Rings ...............................................................................................................7-9
Connecting Rods ...........................................................................................7-10
Crankshafts and Camshafts ..........................................................................7-11
Mechanical Compression Release ................................................................7-12
Valve Lifters ...................................................................................................7-13
Crankcase Breather.......................................................................................7-13
Cylinder Cover...............................................................................................7-13
Page
ENGINE ASSEMBLY
Engine Assembly.....................................................................................................8-1
TROUBLESHOOTING AND TESTING
Engine Knocks.........................................................................................................9-1
Engine Overheats....................................................................................................9-1
Surges or Runs Unevenly........................................................................................9-1
Engine Misfires ........................................................................................................9-1
Engine Vibrates Excessively....................................................................................9-2
Breather Passing Oil................................................................................................9-2
Excessive Oil Consumption.....................................................................................9-2
Lack Power..............................................................................................................9-2
ENGINE SPECIFICATIONS
TVT691 Engine Specifications...............................................................................10-1
Torque Specifications ............................................................................................10-3
Service Tool List ....................................................................................................10-4
iv
CHAPTER 1. GENERAL INFORMATION
ENGINE IDENTIFICATION
Tecumseh engine model, specification, and date of
manufacture (D.O.M.) are located on decals attached to
the blower housing of the engine. The engine
identification decal also provides the applicable warranty
code, oil and fuel recommendations, EPA (Environmental
Protection Agency) and C.A.R.B. (California Air Resource
Board) Emission Compliance Information. (Illust. 1-1)
The group of numbers following the model number is
the specification number. The last three numbers
indicate a variation to the basic engine specification.
(Illust. 1-3)
SPECIFICATION
NUMBER
1-3
1-1
INTERPRETATION OF ENGINE
IDENTIFICATION
The letter designations (TVT) in a model number
indicate the basic type of engine.
The number designations following the letters (691)
indicate the basic engine model displacement in CC’s
(cubic centimeters). (Illust. 1-2)
ENGINE
MODEL
NUMBER
The letter in parenthesis on the engine information decal
is the warranty code identification number. This letter
designates the length of time the engine is under
warranty. A cross-reference may be found in the service
warranty policy of the master repair manual or the engine
operator’s manual. (Illust. 1-4)
WARRANTY
IDENTIFICATION
NUMBER
1-4
1-2
1-1
The D.O.M. (date of manufacture) indicates the
production date of the engine by year and numerical day.
(Illust. 1-5)
DATE OF
MANUFACTURE
(D.O.M.)
1-5
This symbol points out important safety
INSTRUCTIONS, WHICH IF NOT FOLLOWED,
could endanger the personal safety of YOU and
others. Follow all instructions.
SHORT BLOCKS
New short blocks are identified by a tag marked S.B.V.
(Short Block Vertical) located on the engine block. When
a short block repair is made, it is vital both the original
engine and short block numbers are present on the
repaired product for correct future parts identification.
(Illust. 1-6)
SBV OR SBH IDENTIFICATION NUMBER
SHORT BLOCK IDENTIFICATION TAG
SBV- 564A
SER 5107
Using model TVT691-600401A D.O.M. 9146 as an
example, the interpretation is as follows:
TVT691- Is the model number.
60041A Represents the specification number used for
properly identifying the parts of the engine.
TVT Tecumseh Vertical Twin.
691 Indicates the displacement in cubic
centimeters.
9146 Is the D.O.M. (Date of Manufacture) formerly
serial number.
9 Is the last digit in the year of manufacture
(1999).
146 Indicates the calendar day of that year (146th
day or May 26th of 1999).
A,B,C A letter following the D.O.M. number
represents the line, shift and plant in which
the engine was built.
Emissionized engines that meet the California Air
Resource Board (C.A.R.B.) or the Environmental
Protection Agency (EPA) standards will include additional
required engine information on the engine decal.
NOTE: To maintain the best possible emission
performance, use only Genuine Tecumseh Parts.
SERIAL NUMBER
1-6
FUELS
Tecumseh Products Company strongly recommends the
use of fresh, clean, unleaded regular gasoline in all
Tecumseh engines. Unleaded gasoline burns cleaner,
extends engine life, and promotes good starting by
reducing the build up of combustion chamber deposits.
Unleaded regular, unleaded premium or reformulated
gasoline containing no more than 10% Ethanol, 15%
MTBE or 15% ETBE may be used.
Leaded fuel is not available in the United States and
should not be used if any of the above options are
available.
Never use gasoline, fuel conditioners, additives or
stabilizers containing methanol, white gas, or fuel blends,
which exceed the limits, specified above for Ethanol,
MTBE, or ETBE because engine/fuel system damage
could result.
CAUTION: THE USE OF SOME ANTI-ICING
ADDITIVES MAY CREATE A METHANOL FUEL
BLEND. DO NOT USE ADDITIVES THAT
CONTAIN METHANOL. FUEL CONDITIONERS
THAT CONTAIN ISOPROPYL ALCOHOL CAN
BE USED IN CORRECT MIXTURE RATIOS.
Regardless of which of the approved fuels are used, fuel
quality is critical to engine performance. Fuel should
not be stored in an engine or container more than 30
days prior to use. Time may be extended with the use of
a fuel stabilizer like TECUMSEH, part number 730245.
See “STORAGE” instructions in this Manual, Operators
Manual, or Bulletin 111.
1-2
ENGINE OIL
TECUMSEH FOUR-CYCLE ENGINES REQUIRE THE
USE OF CLEAN, HIGH QUALITY DETERGENT OIL.
Be sure original container is marked: A.P.I. service “SF”
thru “SJ” or “CD”.
TECUMSEH RECOMMENDS USING ONE OF THE
FOLLOWING FOUR CYCLE OILS THAT ARE
SPECIALLY FORMULATED TO TECUMSEH
SPECIFICATIONS.
DO NOT USE SAE 10W40 OIL.
FOR SUMMER (Above 320 F) (0oC) USE SAE 30 OIL.
PART 730225
Use SAE 30 oil in high temperature, high load
applications. Using multigrade oil may increase oil
consumption.
Oil Change Procedure: Locate the oil drain plug in the
mounting flange. The drain plug or cap on most units is
located above the frame in one of the locations shown.
(Illust. 1-7) The oil filter if equipped, can be removed
with a commercially available filter wrench.
FOR WINTER (Below 320F) (0oC) USE SAE 5W30 OIL.
PART 730226
(SAE 10W is an acceptable substitute.)
(BELOW 00F (-18oC) ONLY): SAE 0W30 is an
acceptable substitute.
Oil Capacity
Engine Model oz. ml.
TVT691 with Filter 80 2366
TVT691 Oil Only 72 2129
Change oil and filter after the first two operating hours.
Standard oil change intervals are every 50 hours. Oil
filter changes are recommended every 100 operating
hours.
Oil Change Intervals: Change the oil and filter after
the first 2 hours of operation. Thereafter oil change
intervals are every 50 hours. Oil and oil filter changes
are requested every 100 operating hours. Service should
be performed more often if operated under extremely
dusty or dirty conditions. The oil and filter (if equipped)
should be changed yearly if operated less than 100 hours.
Oil Check: Check the oil each time the equipment is
used or every five-(5) hours of operation. Position the
equipment so the engine is level when checking the oil
level.
CAUTION: A TWIN CYLINDER ENGINE MAY
START AND RUN ON ONLY ONE CYLINDER.
ALWAYS DISCONNECT BOTH SPARK PLUG
WIRES FROM THE SPARK PLUGS AND
GROUND TO THE DEDICATED RETAINING
POSTS LOCATED ON THE VALVE COVER
BOXES BEFORE ATTEMPTING ANY SERVICE
OR MAINTENANCE WORK ON THE ENGINE OR
EQUIPMENT.
ALTERNATE
LOCATION
STANDARD OIL DRAIN PLUG LOCATION
NOTE: An oil change is best performed after the engine
is warm.
Remove the oil plug or cap and allow the oil to drain into
a proper receptacle. Always make sure that drain oil and
filter are disposed of properly. Contact your local
governing authorities to find a waste oil disposal site.
Once the oil is drained, reinstall the drain plug and fill the
engine with new oil to the proper capacity.
1-7
BASIC MAINTENANCE CHART
Pre-filter (Dry Poly) Clean every 25 hours
Air filter (Paper Element) Replace every 100 hours of
operation
Oil change Every 50 hours or annually
Oil filter Every 100 hours or
annually
Spark plug replacement Every 100 hours or
annually
Clean cooling fins Every 200 hours or
annually
Fuel Filter (Replace) Every 100 hours or
annually
1-3
BASIC TUNE-UP PROCEDURE:
NOTE: Today’s fuels can cause many problems in an
engines performance due to the fuel quality and short
shelf life (as little as 30 days). Always check fuel as a
primary cause of poor engine performance before
performing any other service.
The following is a minor tune-up procedure. When this
procedure is completed, the engine should operate
properly. Further repairs may be necessary if the engine’s
performance remains poor.
CAUTION: REMOVE THE SPARK PLUG WIRES
AND ATTACH TO THE DEDICA TED RET AINING
POSTS BEFORE DOING ANY SERVICE WORK
ON THE ENGINE.
1. Service or replace the air cleaner. See Chapter 2
under “Service”.
2. Inspect the level and condition of the oil, change or
add oil as required.
3. Remove the blower housing and clean all dirt, grass
or debris from the intake screen, Cylinder head,
cooling fins, carburetor, governor levers and linkage.
4. Check that the fuel filter, fuel tank, and fuel line are
clean. We recommend replacing the fuel filter every
100 hours or annually.
5. Replace the spark plugs every 100 hours or annually,
consult the parts breakdown for the correct spark
plug to be used. Set the spark plug gap (.030") (.762
mm) and install the plug, being careful not to cross
thread. Tighten the spark plug to 21 foot pounds
(28 Nm) of torque. If a torque wrench is not
available, turn the spark plug in as far as possible
by hand, then use a spark plug wrench to turn the
plug 1/2 turn further. If installing a used plug, only
1/8 to 1/4 turn after seat is needed. Note: The correct
plug reach must be used see (Illust. 1-8).
6. Make sure all ignition wires are free of abrasions or
breaks and are properly routed so they will not rub
on the flywheel.
7. Completely clean the cooling fins, intake screen and
linkages of all dirt and debris. Reinstall the blower
housing, fuel tank, fuel line, and air cleaner assembly
if removed. Be careful not to pinch any of the
wires upon re-assembly.
8. Make sure all remote cables are correctly routed and
adjusted for proper operation. See Chapter 4, under
“Speed Controls and Linkage”.
9. Reinstall the spark plug wires, add fuel and oil as
necessary, start the engine.
STORAGE
(IF THE ENGINE IS TO BE UNUSED FOR 30 DAYS
OR MORE)
CAUTION: NEVER STORE THE ENGINE WITH
FUEL IN THE TANK INDOORS OR IN
ENCLOSED, POORLY VENTILATED AREAS,
WHERE FUEL FUMES MAY REACH AN OPEN
FLAME, SPARK OR PILOT LIGHT AS ON A
FURNACE, WATER HEATER, CLOTHES
DRYER OR OTHER GAS APPLIANCE.
Gasoline can become stale in less than 30 days and
form deposits that can impede proper fuel flow and engine
operation. To prevent deposits from forming, all gasoline
must be removed from the fuel tank and the carburetor.
An acceptable alternative to removing all gasoline, is by
adding Tecumseh fuel stabilizer, part number 730245,
to the gasoline. Fuel stabilizer is added to the fuel tank
or storage container. Always follow the mix ratio found
on the stabilizer container. Run the engine at least 10
minutes after adding the fuel stabilizer to allow it to
reach the carburetor. (Illust. 1-9)
STANDARD
PLUG
1-4
OHV
1-8
1-9
CHAPTER 2. AIR CLEANERS
GENERAL INFORMATION
The air cleaner is the device used to eliminate dust and
dirt from the air supply. Filtered air is necessary to assure
that abrasive particles are removed before entering the
combustion chamber. Dirt allowed into the engine will
quickly wear the internal components and shorten engine
life.
The TVT series engine uses a paper-type air filter system
and also has a dry foam pre-filter.
Extremely dirty conditions require more frequent pre-filter
cleaning or paper element replacement.
OPERATION
The air filter cover secures and seals the paper filter
element in place. The cover also prevents large particles
from entering the filter body and completes the KleenAire® circuit. The air is first filtered through the flywheel
and blower housing then enters the air filter cover. It
travels through the pre-filter then the paper filter element.
Pre-filters typically extend the paper filter life.
(Illust. 2-1)
COMPONENTS
The cover holds the poly pre-cleaner and clamps the
paper filter in place, creating a dirt tight seal. The cover
also prevents large debris from entering the filter body.
The pre-cleaner is made of a polyurethane foam and
designed to pre-filter the air prior to it passing through
the paper filter. This added stage, assures the operator
of maximum air filtering and extends paper filter life.
The paper filter element is the main filter to stop
impurities from entering the engine. This dry-type element
is pleated paper for increased surface area maximizing
its life. The filter has rubberized edges to assure sealing.
(Illust. 2-2)
2-1
2-2
TROUBLESHOOTING AND TESTING
If the engine’s performance is unsatisfactory (runs
unevenly, starts smoking abnormally or loses power),
the first engine component(s) to be checked are the air
filter(s). A dirt restricted or oil soaked filter will cause
noticeable performance problems. Polyurethane pre-filter
can be cleaned following the service procedure listed
under “Service” in this chapter. A paper-type air filter can
only be replaced NEVER attempt to clean a paper filter.
The paper-type filter must not have any oil film or residue
present. Should the paper have a brown tint it may have
been damaged by an excessively oiled pre-filter or
crankcase breather problems. Follow the procedure listed
in the “Service” section of this chapter for filter
replacement or cleaning.
2-1
SERVICE
Cleaning of the polyurethane pre-filter element is
recommended every twenty-five (25) operating hours or
(3) months, whichever comes first. Extremely dirty or
dusty conditions may require daily cleanings.
2. Remove the paper filter. Note: Paper filters must be
replaced NEVER attempt to clean a paper filter.
3. Remove the polyurethane pre-cleaner from the
cover.
NOTE: Do not oil the pre-filter, paper element damage
can occur.
The paper filter element should be replaced once a year
or every 100 operating hours, more often if used in
extremely dusty conditions.
NOTE: Never run the engine without the complete air
cleaner assembly installed on the engine. Always replace
the filter element with a Tecumseh original replacement
part to maintain proper filtration, emissions compliance
and long engine life.
Disassembly Procedure
1. Remove the wing nuts holding the air cleaner cover
in place. Swing the cover out, then lift to remove.
(Illust. 2-3)
BODY
(ATTACHED TO ENGINE)
PAPER FILTER
FOAM PRE-FILTER
WING NUTS (2)
4. Wipe or wash out the air filter cover and base. (Illust.
2-4)
2-4
5. Service the polyurethane pre-filter element by
washing in liquid dish soap and warm water until
clean. Squeeze out the excess water (Never Twist).
Finish drying the element by squeezing it in a dry
cloth or paper towel.
SLOTS
TABS
COVER
2-3
NOTE: DO NOT OIL THE PRE-FILTER IT MUST
BE INSTALLED DRY TO PREVENT SATURATION
OF THE PAPER FILTER ELEMENT.
6. Install the pre-cleaner and new air filter in the cover.
Replace the filter cover and tighten the wing nuts,
be careful not to over-tighten it. Note: The air filter
system on all models can be upgraded to include
the pre-cleaner if the OEM did not originally request
one.
2-2
CHAPTER 3. CARBURETORS AND FUEL SYSTEMS
GENERAL INFORMATION
The TVT engine uses two series seven (7) float type
carburetors. This carburetor uses a choke enrichment
system to provide easy cold engine starting. To comply
with emission standards, the carburetor idle and highspeed fuel mixtures are non-adjustable. Carburetor
cleaning and related fuel system service is covered in
this chapter.
FLOAT STYLE CARBURETORS
A float is used to maintain the operating level of fuel in
the carburetor bowl. As the engine consumes fuel, the
fuel level in the carburetor bowl drops and the float moves
downward. This allows the inlet needle valve to move off
the sealing seat, and fuel to enter the carburetor float
bowl. As the fuel level in the bowl rises, it elevates the
float. This upward float motion moves the inlet needle
valve to the closed position. When the needle contacts
the seat, the fuel flow is stopped. The tapered end of the
inlet needle varies the fuel flow rate keeping the supply
constant. (Illust. 3-1) The float height on the series 7
carburetor is fixed and may not be adjusted.
OPERATIONAL CIRCUITS SERIES 7
CARBURETOR
SERIES 7
IDLE
PRIMARY
IDLE MIXING
WELL
IDLE
RESTRICTOR
IDLE/TRANSFER
FUEL
PASSAGE
IDLE PROGRESSION HOLES
IDLE
AIR BLEED
SPRING
MAIN JET
ATMOSPHERIC
VENT PASSAGES
MAIN NOZZLE
AIR BLEED
3-2
INLET
NEEDLE
3-1
NOTE: Gravity fed systems must have the bottom of
the fuel tank no lower than the fuel inlet of the carburetor.
When servicing carburetors, use the engine model and
specification number to obtain the correct carburetor part
number or parts. An alternate method is to use the
manufacturing number stamped on the carburetor.
Convert this number to a service part number in Div. 5
carburetor section of the Master Parts Manual. This
method can also be used in microfiche and computer
parts look-up systems.
Choke Circuit: In the “CHOKE”/“START” position, the
choke shutter is closed, and the only air entering the
engine, enters through openings around the shutter. As
the starting device cranks the engine over, the pistons
travel downward on the intake stroke, creating a lowpressure area in the cylinder. High-pressure
(atmospheric) air rushes into the cylinder to fill the lowpressure area created.
Since the choke shutter blocks the majority of the air
passage, a relatively small quantity of air enters the
carburetor. The main nozzle and idle fuel discharge ports
are all supplying fuel at this point. This is due to the
increased low air pressure in the intake system of the
engine. A maximum fuel flow through the carburetor
orifices combined with the reduced quantity of air that
passes through the carburetor, creates a very rich fuel
mixture needed to start a cold engine.
3-1
Governed Idle Circuit: The TVT series engine uses a
governed idle system. In the low speed throttle position,
engine speed is being maintained by the governor NOT
the idle speed adjustment screw. The governed idle
system improves throttle response when the engine load
changes. The relatively small amount of fuel/air mixture
is supplied through the primary idle orifice location under
the idle mixing well welch plug. (Illust. 3-3)
IDLE SPEED
ADJUSTMENT
IDLE
MIXING
WELL
SCREW
3-3
True Idle: The idle speed adjustment screw on governed
idle engines perform as a stop to prevent complete
closure of the throttle plate. This partial open throttle
position is required for good starting performance. The
idle adjustment screw is set 600 RPM lower than the
governed idle speed. (Found on microfiche card #30 or
the computer parts look-up systems.) See governed
speed adjustment procedure Chapter 4.
CAUTION: DUAL CARBURETORS MUST BE
PROPERLY SYCRONIZED. DO NOT ADJUST
IDLE SPEED SCREW WITHOUT PROPER
SYNCHRONIZATION.
Transfer/Intermediate Circuit: During Intermediate
engine operation or light loads, additional orifices are
uncovered in the idle mixing well, as the throttle shutter
opens. The fuel being released from these jets is already
pre-mixed (atomized) with air prior to entering the air
stream in the venturi of the carburetor. When the fuel
enters the air stream it further mixes with the air which
maximizes combustibility.
Idle Mixing Well: The idle mixing well of the carburetor
contains a series of metering holes. These metering holes
are the primary and secondary idle circuit as well as the
idle air bleed hole. Proper servicing of the carburetor
requires removal of the welch plug and cleaning of these
metering holes. (Illust. 3-4)
IDLE
MIXING WELL
IDLE SPEED
ADJUSTMENT
SCREW
3-4
High Speed Circuit: During HIGH-SPEED engine
operation, the throttle shutter is opened beyond the idle/
transfer discharge ports. Air is flowing through the
carburetor(s) at a high rate. The venturi, which decreases
the size of the air passage through the carburetor, causes
the airflow to further accelerate. This rapidly moving air
creates a low-pressure area at the main nozzle (Emulsion
Tube) discharge opening.
Using air that is channeled to the emulsion tube through
the main nozzle air bleed, a mixture of fuel and air is
drawn up the emulsion tube.
The addition of air creates an atomized mixture before
being discharged into the venturi. Fuel flow is created
by the difference in the atmospheric air pressure on the
fuel in the carburetor bowl and the main nozzle opening.
Atmospheric Vent: For the fuel to flow out of the
carburetor, the bowl must be vented to atmospheric
pressure. The internal vent is located at the 4 o’clock
position from the choke end of the carburetor. (Illust.
3-5) This passage should be checked for blockage if
engine performance is in question.
ATMOSPHERIC
VENT
3-2
3-5
Main Nozzle Air Bleed: Air is bled into the main nozzle
through the main nozzle air bleed passage located in
the 6 o’clock position of the carburetor’s choke end. (Illust.
3-6) This passage allows air to mix with the fuel traveling
up the main nozzle creating a pre-atomized mixture. The
fuel is then released into the venturi from the nozzle tip.
Atomization occurs as the fuel mixture contacts the fast
moving air stream in the venturi and flows into the intake
of the engine.
TESTING
1. Should repeated efforts to start the engine using the
procedure listed in the operator’s manual fail, check
for spark by removing the high-tension lead. Install
an ignition tester and check for spark. If the spark is
bright blue and consistent, proceed to step 2. If no
or irregular spark see Chapter 6 under “Testing”.
CAUTION: KEEP ALL COMBUSTIVE SOURCES
AWAY. AVOID THE SPRAY FROM THE SPARK
PLUG HOLE WHEN CRANKING THE ENGINE
OVER AND MAKE SURE THE PLUG WIRES ARE
PROPERLY GROUNDED TO THE DEDICATED
RETAINING POSTS.
2. Remove and visually inspect the condition of each
spark plug, a wet condition indicates the presence
of gasoline in the cylinder. Although this indicates
fuel is present the fuel condition regarding its
combustibility should always be checked.
NOTE: Check plug for correct reach. (Illust. 3-8)
3-6
Low Speed Idle Air Bleed: The low speed circuit of the
carburetor has an idle air bleed passage which performs
the same function as the high-speed air bleed. It premixes fuel and air prior to entering the throat of the
carburetor. This passage is located in the idle mixing
well (Illust. 3-7)
LOW SPEED
IDLE AIR BLEED
IDLE MIXING
WELL
PLUG
OHVSTANDARD
3-8
3. If either spark plug is dry, check for restrictions in
the fuel system, which supplies that cylinder. If both
plugs are dry check the fuel supply system and
continue with step #4. If the spark plug is wet,
continue with step # 8.
4. Dry Spark Plug: Begin by checking the fuel cap for
proper atmospheric venting. With the fuel cap in place
and tightened, remove the fuel line prior to the pump
allowing fuel to flow into a proper receptacle. Allow
at least 1 gallon of fuel to flow out, noting the rate of
flow. If it remains consistent the vent is performing
properly. Re-connect the fuel line(s) to the pump.
3-7
NOTE: Today’s fuels can cause many problems in
engine performance due to the fuels quality and short
shelf life. Always check fuel as a primary cause of
engine poor performance.
5. Remove the air filter, visually check the choke
shutter(s) operation for complete closure when the
throttle or independent choke control are in the full
choke position.
3-3
6. Fuel Supply If the fuel flow to the carburetors is
adequate and no fuel is evident at either spark plug,
the carburetor bowl(s) will need to be removed for
service. See “Service” in this chapter or consult the
“Carburetor Troubleshooting” chart to diagnose
carburetor symptoms. Improper fuel flow indicates
the fuel, fuel line, filter or tank require cleaning or
replacement.
7. Compression Test Most Tecumseh engines include
a compression relief system. These systems make
publishing compression values impractical. However,
following is a cylinder compression balance test,
which can be preformed to help diagnose a possible
compression concern.
1. Remove air filter cover, air filter and both spark
plugs
2. Ground out the spark plug wires to the engine.
3. Install a compression tester into either of the
spark plug holes of the cylinder head.
8. Wet Plug(s) A wet spark plug indicates fuel is being
supplied by the carburetor. A restricted air filter,
carbon shorted or defective spark plug, excessive
choking or a defective carburetor, may have flooded
the engine. With the spark plug(s) removed and the
plug wire(s) grounded to the dedicated retaining
posts, place a shop towel over the spark plug hole.
Turn the engine over very slowly by hand to remove
excess gasoline from the engine cylinder.
CAUTION: KEEP ALL COMBUSTIVE SOURCES
AWAY. AVOID THE SPRAY FROM THE SPARK
PLUG HOLE WHEN CRANKING THE ENGINE
OVER AND MAKE SURE THE PLUG WIRES
ARE PROPERLY GROUNDED TO THE
DEDICATED RETAINING POST.
9. Replace the air filter if restricted or oil soaked, if the
paper filter has a brown color it may have been
damaged by oil and should be replaced. Replace
the spark plug if questionable then install the spark
plugs and high tension leads. Attempt to start the
engine.
4. Turn engine over until the highest reading is
recorded on the compression tester.
5. Write down the reading, remove the compression
tester install it into the remaining cylinder head
and repeat.
Compare the two readings. The difference between
the two cylinders should not exceed 20%. Example:
Cyl #1 90 PSI, Cyl #2 75 PSI. There is 15-PSI
difference between cylinders. Divide this number (15)
into the highest compression reading (90) giving a
17% difference between cylinders. A difference
above 20% or an extremely low compression reading
(below 50 PSI) will require further leak testing or
cylinder head removal for inspection.
Cylinder #1 Cylinder #2 Difference %
90 psi - 75 psi = 15 psi ÷ 90 = 17%
10. If the engine floods and fails to start, the carburetor(s)
will require service. See the “Carburetor
Troubleshooting” chart for additional causes. If the
carburetor is functioning properly the problem may
be ignition or timing related. Reference
“Troubleshooting” under “Ignition” for further
assistance.
3-4
CARBURETOR DISASSEMBLY
PROCEDURE
Before performing any carburetor service check the
throttle/choke control(s) for proper adjustments. Make
sure the unit is reaching full choke shutter position on
both carburetors.
NOTE : The series seven carburetor uses FIXED IDLE
AND MAIN JETS AND SHOULD BE SERVICED ONLY
BY QUALIFIED TECHNICIANS TO PREVENT
DAMAGE. It is a violation of both the U.S. EPA and CARB
regulations to modify the carburetor from the original
factory jetting unless specifically authorized.
CAUTION: DRAIN THE FUEL INTO AN
APPROVED CONTAINER OUTDOORS, AND
AWAY FROM ANY OPEN FLAME OR
COMBUSTION SOURCE. BE SURE THE ENGINE
IS COOL.
1. Remove the fuel line. Use care not to damage the
float bowl or retainer. Disconnect the wires from the
fuel shut-off solenoids. Release the float bowl retainer
bail. The float bowl assembly may now be removed
by pulling straight down. (Illust. 3-9)
2. Remove the main nozzle (Emulsion) tube, “O” ring,
and spring located in the center leg of the float bowl.
(Illust. 3-10)
SPRING
O-RING
MAIN NOZZLE
(EMULSION TUBE)
3-10
3. Next remove the bowl drain screw or fuel shut off
solenoid and gasket. Remove the spring, metering
jet, and “O” ring. (Illust. 3-11)
SOLENOID
GASKET
METERING
JET
3-9
SPRING
O-RING
3-11
4. Float removal is done by grasping the cross-brace
on the float with needle nose pliers. Then pulling in a
horizontal motion to release the float assembly. (Illust.
3-12) Removal by any other method may cause
damage.
3-12
3-5
5. Remove the inlet needle seat using a No. 4 crochet
hook or a paper clip with a 3/32" (2.38 mm) hook
end. Push the hook through the hole in the center of
the seat and pull out to remove it. NOTE: A metal
retaining ring may be present on top of the seat to
aid in its retention, this will come out with the seat. If
a ring is present or comes with the new seat reinstall
it. (Illust. 3-13)
NOTE: Before removing the main carburetor body,
mark or sketch the choke and throttle linkage
connection points. Also MARK THE EDGES OF THE
THROTTLE AND CHOKE SHUTTERS. THE
SHUTTERS HAVE BEVELED EDGES AND MUST
BE INSTALLED IN THE ORIGINAL POSITION.
7. Use a Torx T-10 to remove the choke and throttle
shutters. Remove the throttle shaft, choke shaft and
return springs.
8. Welch plug Removal: Secure the carburetor in a vise
equipped with protective jaws. Use a small chisel
sharpened to a 1/8" (3.175 mm) wide wedge point .
Drive the chisel into the plug to pierce the metal and
push down on the chisel prying the plug out of the
hole. (Illust. 3-15)
NOTE: Be careful not to drive the chisel through the
plug damaging the metering holes underneath.
3-13
6. Idle Restrictor: The idle restrictor is located to the
side of the center leg in the fuel bowl. (Illust. 3-14)
Clean the passage using a piece of wire (maximum
.015, .0006 mm), carburetor spray and compressed
air, verify it is open. If the restrictor remains plugged
it can be serviced by replacement of the float bowl
assembly only.
NOTE: New service fuel bowls come with the
restrictor installed.
SMALL
CHISEL
PRY OUT
PLUG
DO NOT ALLOW
CHISEL POINT
TO STRIKE
CARBURETOR
BODY OR
CHANNEL
REDUCER
PIERCE PLUG
WITH TIP
SMALL CHISEL
WELCH PLUG TO
BE REMOVED
ABOUT 1/8”
(3.175 mm)
WIDE
3-15
3-6
3-14
INSPECTION
After careful disassembly of the carburetor, clean the
carburetor body and float bowl with solvent, or spray
carburetor cleaner. Wearing eye protection, use
compressed air and soft tag wire to clean internal
carburetor passages. (Illust. 3-16) Examine the float for
cracks or leaks. Check the float hinge bearing surfaces
for wear, as well as the tab that contacts the inlet needle.
Examine the throttle, choke shaft, and carburetor body
at the bearing points and holes into which the linkage is
fastened. If dust seals are present, check the seal
condition and for correct placement next to the carburetor
body. If the condition of any of these parts is worn or
questionable replace them. The float can be checked
for leakage by submersion in a clear jar filled with hot
water. If any air bubbles are noted the float must be
replaced.
NOTE: DO NOT INTERCHANGE MAIN NOZZLES OR
METERING JETS FROM OTHER CARBURETORS.
CARBURETOR RE-ASSEMBLY
WELCH PLUGS
To install a new welch plug, secure the carburetor in a
vise equipped with protective jaws. Place the welch plug
into the mixing well pocket with the raised portion up.
With a punch equal to the size of the plug-hole, flatten
the plug. Do not dent or drive the center of the plug below
the top surface of the carburetor. After installation of the
welch plug, seal the outer diameter with fingernail polish.
(Illust. 3-17)
3-16
3-17
THROTTLE SHAFT AND PLATE
When reassembling the throttle plate on a series 7
carburetor, it is important that the marking on the plate
be in the 3 o’clock position facing out with the throttle
plate closed. (Illust. 3-18)
3 O’CLOCK
POSITION
3-18
3-7
CHOKE SHAFT AND PLATE
Install the choke return spring on the choke shaft with
the squared end up and hooked into the notch on the
arm. Work the dust shield up around the spring and insert
the choke shaft into the carburetor body. Rotate the shaft
counterclockwise until the tang on the spring rests against
the left side center boss on the carburetor body. (Illust.
3-19)
FUEL BOWL ASSEMBLY
Inlet Needle & Seat
When servicing the fuel bowl assembly, a new needle
and seat should always be installed to reduce the
possibility of leakage.
Make sure the seat cavity is clean. Moisten the seat
with oil and insert the seat with the grooved side down
and away from the inlet needle. Press the seat into the
cavity using a 5/32” (3.969 mm) an Allen wrench or a
flat punch, making sure it is firmly seated. (Illust. 3-20) If
the new needle and seat contains a retainer install it on
top and in contact with the seat.
3-19
Always use new shutter screws part 650506 when
reinstalling a shutter plate. Install the screws so they
are slightly loose. Apply light downward pressure on the
shaft and rotate it clockwise to seat the shutter in the
bore, then tighten the shutter screws. Check for binding
by rotating the shaft. If necessary, adjust the shutter by
loosening and repositioning, then retighten the screws.
3-20
Main Jet Assembly
Install a new O-ring in the main jet cavity (verify the
original o-ring has been removed). Place the spring over
the shoulder of the main jet and insert into the cavity
with the main jet towards the o-ring. Next install a new
fiber gasket on the bowl drain screw or fuel shut-off
solenoid and tighten to 25-30 In. lbs. (2.83 - 3.4 Nm).
(Illust. 3-21)
SOLENOID
GASKET
METERING
JET
3-8
SPRING
O-RING
3-21
Main Nozzle (Emulsion Tube)
Place the main nozzle tension spring into the cavity of
the float bowl. Apply a small amount of oil to the o-ring
on the main nozzle and insert it into the float bowl cavity.
Float Installation
Install the float with a new inlet needle and float hinge
pin onto the float bowl assembly. Carefully push the hinge
pin into the retaining post using a small flat blade
screwdriver. Check the float movement for complete
travel.
IMPULSE FUEL PUMPS
11
1
10
4
7
NOTE: EMISSIONIZED ENGINES OPERATED WITHIN
THE UNITED STATES MAY HAVE HIGH ATTITUDE
JETS AVAILABLE, CONSULT SERVICE BULLETIN
110 FOR INFORMATION.
Final Checks
Test the inlet needle and seat sealing using Tecumseh
service kit 670340 or a similar pop-off tester. To test the
pop off pressure remove the float bowl, float and inlet
needle. Place a drop of fuel on the seat and reinstall the
needle and float. Hook up the pressure tester and apply
approximately 6-9 PSI of pressure or until the needle
pops off the seat. Slowly release the pressure to not
less than 1 ½ PSI. The needle should seat between
1 ½ - 6 PSI for a minimum of five minutes. If the minimum
1 ½ PSI cannot be maintained the needle and seat will
need to be serviced. (Illust. 3-22)
11
5
1 - Body, Impulse
2 - Body, Pump
3 - Cover, Pump
4 - Bearing, Spring
5 - *Valve, Check (2)
6 - *Gasket, Pump Cover
7 - *Diaphragm, Pump (2)
9 - Screw, 1-1/4" (4)
10 - *Spring, Pressure
11 - *Filter, Air
9
2
8
6
3
3-23
Impulse fuel pumps are externally mounted in the fuel
circuit between the fuel supply and the carburetor. A fuel
pump must be used if the fuel supply outlet is lower than
the bowl inlet. There MUST be a in-line fuel filter installed
prior to the pump to prevent system damage.
Impulse fuel pumps are operated by positive and
negative pressure pulsation in the crankcase, which are
created by the up, and down movement of the piston. A
hose called a pulse line, connects the fuel pump
diaphragm chamber to the crankcase and transmits the
pulses to the pump diaphragm. These impulses actuate
the diaphragm creating the pumping action to lift the
fuel from the fuel tank to the carburetor(s). (Illust. 3-24)
The pump body contains check valves, which open and
close preventing the fuel from going backwards from
the pump.
Fuel Bowl Retaining Bail
The retainer bail must hold adequate pressure on the
float bowl to prevent air or fuel leakage during operation.
When re-installed, the force should be adequate to
securely clamp the bowl to the body of the carburetor. If
damage occurred upon bowl removal replace the bail.
3-22
VALVE CLOSED
CRANKCASE PRESSURE
ê
ATMOSPHERIC PRESSURE ACTING
á
ON DAMPING DIAPHRAGM
FUEL FLOW
á
ATMOSPHERIC
VENT
FUEL SUPPLY
CRANKCASE SUCTION AND
ê
FLOW DIRECTION
ATMOSPHERIC PRESSURE
ACTING ON DAMPING
á
DIAPHRAGM
CARBURETOR
FITTING
VALVE OPEN
DIAPHRAGM
FILTER
AIR BLEED
VALVE
CLOSED
PULSE LINE
TO CRANKCASE
SUCTION FUEL FLOW
á
DIRECTION
ATMOSPHERIC PRESSURE
ê
CAUSED FUEL FLOW
3-24
3-9
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