Tecumseh V-twin User manual

V-TWIN
ENGINE
TECUMSEH
Small Engine Parts

i
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
Copyright © 2000 by Tecumseh Products Company
All rights reserved. No part of this book may be reproduced or transmitted, in any form or by any
means, electronic or mechanical, including photocopying, recording or by any information storage and
retrieval system, without permission in writing from Tecumseh Products Company Training Department
Manager.

ii
TABLE OF CONTENTS
(bysubject)
GENERAL INFORMATION Page
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
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

iii
Page
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
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
TABLE OF CONTENTS (continued)

iv
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
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
TABLE OF CONTENTS (continued)
Page

1-1
1-1
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
identificationdecalalsoprovidestheapplicablewarranty
code,oilandfuelrecommendations,EPA(Environmental
ProtectionAgency)and C.A.R.B.(CaliforniaAirResource
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)
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)
1-2
Theletterinparenthesison the engine information decal
is the warranty code identification number.Thisletter
designates the length of time the engine is under
warranty. A cross-reference may be found in the service
warrantypolicyof the masterrepairmanualorthe engine
operator’s manual. (Illust. 1-4)
1-3
1-4
ENGINE
MODEL
NUMBER
SPECIFICATION
NUMBER
WARRANTY
IDENTIFICATION
NUMBER

1-2
The D.O.M. (date of manufacture) indicates the
productiondateoftheengineby year and numerical day.
(Illust. 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.
(ShortBlockVertical)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)
1-5
1-6
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.
9Is 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
ProtectionAgency(EPA)standards will includeadditional
required engine information on the engine decal.
NOTE: To maintain the best possible emission
performance, use only Genuine Tecumseh Parts.
FUELS
TecumsehProductsCompanystronglyrecommendsthe
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
stabilizerscontainingmethanol, whitegas,orfuel 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 fuelstabilizerlike TECUMSEH, part number 730245.
See “STORAGE” instructions in this Manual, Operators
Manual, or Bulletin 111.
DATE OF
MANUFACTURE
(D.O.M.)
SBV OR SBH IDENTIFICATIONNUMBER
SHORTBLOCK IDENTIFICATIONTAG
SERIALNUMBER
SBV- 564A
SER 5107

1-3
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
arerequestedevery100operatinghours.Serviceshould
be performed more often if operated under extremely
dusty or dirty conditions. The oil and filter (if equipped)
shouldbechanged yearlyifoperatedlessthan 100hours.
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: ATWIN CYLINDER ENGINE MAY
STARTAND RUN ON ONLYONE 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
ORMAINTENANCEWORKON THE ENGINE OR
EQUIPMENT.
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 320F) (0oC) USE SAE 30 OIL.
PART 730225
Use SAE 30 oil in high temperature, high load
applications. Using multigrade oil may increase oil
consumption.
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
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.
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
aproper receptacle. Always makesure thatdrainoiland
filter are disposed of properly. Contact your local
governing authorities to find a waste oil disposal site.
Oncetheoil is drained, reinstall the drain plugand fill the
engine with new oil to the proper capacity.
BASIC MAINTENANCE CHART
Pre-filter (Dry Poly) Clean every 25 hours
Air filter (Paper Element) Replaceevery100hours 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
1-7
STANDARD OIL DRAIN PLUG LOCATION
ALTERNATE
LOCATION

1-4
1-8
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. Furtherrepairsmaybenecessaryif theengine’s
performance remains poor.
CAUTION: REMOVE THE SPARK PLUG WIRES
AND ATTACH TO THE DEDICATED RETAINING
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,
coolingfins, 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. Replacethespark plugs every100hoursor annually,
consult the parts breakdown for the correct spark
plugtobe 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
1/8to1/4turnafterseatisneeded.Note:Thecorrect
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. Completelycleanthe cooling fins, intake screen and
linkages of all dirt and debris. Reinstall the blower
housing,fueltank, fuelline,andair cleanerassembly
if removed. Be careful not to pinch any of the
wires upon re-assembly.
8. Makesureallremotecables are correctly routed and
adjustedforproperoperation.SeeChapter 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
formdepositsthatcanimpedeproper fuelflowandengine
operation.Toprevent 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)
1-9
STANDARD
PLUG OHV

2-1
2-1
CHAPTER 2. AIR CLEANERS
GENERAL INFORMATION
The air cleaner is the device used to eliminate dust and
dirtfromtheairsupply.Filteredairis necessary toassure
that abrasive particles are removed before entering the
combustion chamber. Dirt allowed into the engine will
quicklyweartheinternalcomponentsandshortenengine
life.
TheTVTseriesengineuses a paper-type airfiltersystem
and also has a dry foam pre-filter.
Extremelydirtyconditions requiremorefrequentpre-filter
cleaning or paper element replacement.
OPERATION
The air filter cover secures and seals the paper filter
elementinplace.Thecoveralsopreventslargeparticles
from entering the filter body and completes the Kleen-
Aire®circuit. The air is first filtered through the flywheel
and blower housing then enters the air filter cover. It
travelsthroughthepre-filterthenthepaperfilterelement.
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
impuritiesfromentering theengine.This dry-typeelement
is pleated paper for increased surface area maximizing
itslife.Thefilterhasrubberized edges to assure sealing.
(Illust. 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
noticeableperformanceproblems.Polyurethanepre-filter
can be cleaned following the service procedure listed
under“Service” in this chapter. Apaper-type airfilter can
onlybereplacedNEVER attempttoclean a paperfilter.
Thepaper-typefiltermustnothave 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
crankcasebreatherproblems. Followtheprocedurelisted
in the “Service” section of this chapter for filter
replacement or cleaning.
2-2

2-2
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.
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
cleanerassemblyinstalledonthe 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)
2-3
2-4
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.
4. Wipeorwash out the air filter cover and base. (Illust.
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.
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.
SLOTS
TABS
BODY
(ATTACHED TO ENGINE)
PAPERFILTER
FOAMPRE-FILTER
WING NUTS (2)
COVER

3-1
3-1
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 high-
speed 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
fuellevelinthe carburetor bowldropsandthefloat 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
3-2
NOTE: Gravity fed systems must have the bottom of
thefueltanknolowerthanthe fuel inlet of the carburetor.
When servicing carburetors, use the engine model and
specificationnumbertoobtainthe 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 low-
pressure area in the cylinder. High-pressure
(atmospheric) air rushes into the cylinder to fill the low-
pressure area created.
Since the choke shutter blocks the majority of the air
passage, a relatively small quantity of air enters the
carburetor. Themainnozzle andidlefueldischargeports
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.
SERIES7
IDLEMIXING
WELL
IDLE
RESTRICTOR
IDLE/TRANSFER
FUEL
PASSAGE
SPRING MAINJET
MAINNOZZLE
AIRBLEED
ATMOSPHERIC
VENTPASSAGES
IDLE
PRIMARY
IDLE
AIRBLEED
IDLE PROGRESSION HOLES
INLET
NEEDLE

3-2
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
systemimprovesthrottleresponsewhentheengineload
changes. The relatively small amount of fuel/air mixture
issuppliedthroughtheprimaryidleorificelocationunder
the idle mixing well welch plug. (Illust. 3-3)
Idle Mixing Well: The idle mixing well of the carburetor
containsaseries ofmeteringholes.These meteringholes
are the primary and secondary idle circuit as well as the
idle air bleed hole. Proper servicing of the carburetor
requiresremovalof the welch plug and cleaning of these
metering holes. (Illust. 3-4)
3-4
True Idle: Theidle speed adjustmentscrewongoverned
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
PROPERLYSYCRONIZED. 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.Thefuel 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
3-5
IDLE
MIXINGWELL
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)ata highrate.Theventuri, whichdecreases
thesizeof theairpassagethrough thecarburetor,causes
the airflow to further accelerate. This rapidly moving air
createsalow-pressureareaatthe mainnozzle(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.
3-3
IDLESPEED
ADJUSTMENT
SCREW
ATMOSPHERIC
VENT
IDLE SPEED
ADJUSTMENT
SCREW

3-3
Main Nozzle Air Bleed: Air is bled into the main nozzle
through the main nozzle air bleed passage located in
the6o’clock positionofthecarburetor’s chokeend.(Illust.
3-6)This passage allows air to mix withthe fuel traveling
upthemainnozzlecreatingapre-atomizedmixture.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.
3-7
Low Speed Idle Air Bleed: The low speed circuit of the
carburetorhas an idle air bleed passagewhich performs
the same function as the high-speed air bleed. It pre-
mixes fuel and air prior to entering the throat of the
carburetor. This passage is located in the idle mixing
well (Illust. 3-7)
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)
3-8
OHVSTANDARD
PLUG
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
properatmosphericventing.Withthefuelcapinplace
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.
NOTE: Today’s fuels can cause many problems in
engineperformancedue to thefuelsqualityand 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.
3-6
IDLEMIXING
WELL
LOWSPEED
IDLE AIR BLEED

3-4
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 MostTecumsehengines include
a compression relief system. These systems make
publishingcompressionvalues 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.
4. Turn engine over until the highest reading is
recorded on the compression tester.
5. Writedownthe reading,removethecompression
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
differencebetweencylinders. Dividethisnumber(15)
into the highest compression reading (90) giving a
17% difference between cylinders. A difference
above20%or an extremelylowcompressionreading
(below 50 PSI) will require further leak testing or
cylinder head removal for inspection.
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.
10. Iftheenginefloods and failstostart,thecarburetor(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.
Cylinder #1 Cylinder #2 Difference %
90 psi -75 psi = 15 psi ÷90 = 17%

3-5
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.Itis a violationofboththeU.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
fuelshut-off solenoids.Releasethe floatbowlretainer
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)
3-9
3-10
SPRING MAINNOZZLE
(EMULSIONTUBE)
O-RING
4. Float removal is done by grasping the cross-brace
onthe float with needle nosepliers.Thenpullingin a
horizontalmotionto releasethefloatassembly.(Illust.
3-12) Removal by any other method may cause
damage.
3-11
3-12
SOLENOID
GASKET
O-RING
SPRING
METERING
JET
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)

3-6
5.Remove the inlet needle seat using a No. 4 crochet
hook or a paper clip with a3/32" (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
aring is present or comes with thenew seat reinstall
it. (Illust. 3-13)
3-13
3-14
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.
NOTE: Before removing the main carburetor body,
mark or sketch the choke and throttle linkage
connectionpoints.Also MARK THEEDGESOFTHE
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. Removethethrottleshaft,choke shaft and
return springs.
8. WelchplugRemoval:Securethe 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.
3-15
SMALL
CHISEL
PRY OUT
PLUG
DO NOT ALLOW
CHISELPOINT
TOSTRIKE
CARBURETOR
BODY OR
CHANNEL
REDUCER
PIERCEPLUG
WITHTIP
WELCH PLUG TO
BEREMOVED
ABOUT1/8”
(3.175mm)
WIDE
SMALLCHISEL

3-7
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
forwear,as well as the tabthatcontactstheinlet 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
conditionandfor correct placementnexttothe 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.
3-16
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
theplug.Donotdentordrivethecenteroftheplugbelow
the top surface of the carburetor. After installation of the
welchplug,sealtheouterdiameterwithfingernailpolish.
(Illust. 3-17)
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)
3-18
3O’CLOCK
POSITION

3-8
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.Workthedustshield up around the springandinsert
thechokeshaftinto the carburetor body. Rotate the shaft
counterclockwiseuntilthe tangonthespring restsagainst
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
Main Jet Assembly
Install a new O-ring in the main jet cavity (verify the
originalo-ring has been removed). Place thespring 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)
3-20
3-21
SOLENOID
GASKET
O-RING
SPRING
METERING
JET
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.

3-9
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
pinontothefloatbowlassembly.Carefully push the hinge
pin into the retaining post using a small flat blade
screwdriver. Check the float movement for complete
travel.
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 foraminimumoffiveminutes.Iftheminimum
1 ½ PSI cannot be maintained the needle and seat will
need to be serviced. (Illust. 3-22)
3-22
3-23
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
3
6
8
11
52
11
1
10
7
4
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.
IMPULSE FUEL PUMPS
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
thebowlinlet.ThereMUST be a in-line fuelfilterinstalled
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.
3-24
CRANKCASE PRESSURE
ATMOSPHERIC PRESSURE ACTING
ON DAMPING DIAPHRAGM
FUEL FLOW
CRANKCASE SUCTION AND
FLOW DIRECTION
ATMOSPHERIC PRESSURE
ACTING ON DAMPING
DIAPHRAGM
SUCTION FUEL FLOW
DIRECTION
ATMOSPHERIC PRESSURE
CAUSED FUEL FLOW
á
á
á
áê
ê
ê
VALVECLOSED
ATMOSPHERIC
VENT
CARBURETOR
FITTING
VALVEOPEN
DIAPHRAGM
FILTER
PULSELINE
TOCRANKCASE
VALVE
CLOSED
AIRBLEED
FUELSUPPLY