Tecumseh Overhead Valve Engine Manual


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TECUMSEH

T E C H N I C I A N ' S H A N D B O O K

This manual covers engine models:

OHH50 - 65, OHHSK50 - 130, OHV11 - OHV17, OVM120,

OVRM40-675, OVRM120, OVXL/C120, OVXL120, OVXL125.

Other illustrated Tecumseh 2-Cycle Engine, 4-Cycle Engine and Transmission manuals; booklets; and wall charts are available through Tecumseh.

For complete listing write or call

CONTAINS SEARS CRAFTSMAN CROSS REFERENCE

4-CYCLE OVERHEAD VALVE

ENGINES

CONTENTS

 

Page

INLET NEEDLE AND SEAT

20

FLOAT INSTALLATION

20

FUEL BOWL AND BOWL NUT

21

IMPULSE FUEL PUMP

21

PRIMER BULB

21

FINAL CHECKS

21

CHAPTER 4 GOVERNORS AND LINKAGE

22

GENERAL INFORMATION

22

OPERATION

22

TROUBLESHOOTING

22

ENGINE OVERSPEEDING

22

ENGINE SURGING

22

SERVICE

23

GOVERNOR ADJUSTMENT

23

GOVERNOR GEAR AND SHAFT SERVICE

23

GOVERNOR GEAR OR SHAFT REPLACEMENT,

 

UPSET STYLE GOVERNOR SHAFT

23

GOVERNOR SHAFT REPLACEMENT, RETAINING

 

RING STYLE

24

SPEED CONTROLS AND LINKAGE

25

CONVERSION TO REMOTE CONTROL

27

OVM, OVXL, OHV VERTICAL SPEED CONTROL

28

OHV 11-17 HORIZONTAL SPEED CONTROL

28

CHAPTER 5 RECOIL STARTERS

29

GENERAL INFORMATION

29

OPERATION

29

COMPONENTS

29

SERVICE

29

ROPE SERVICE

29

ROPE RETAINER REPLACEMENT

30

STYLIZED REWIND STARTER (OHH, OVRM, OHM,

 

OHSK, OVM, OVXL, OHV 11-13), AND STAMPED

 

STEEL STARTER

30

DISASSEMBLY PROCEDURE

30

ASSEMBLY PROCEDURE

31

STYLIZED REWIND STARTER WITH PLASTIC

 

RETAINER

31

DISASSEMBLY PROCEDURE

31

ASSEMBLY

32

KEEPER SPRING STYLE STARTERS

32

DISASSEMBLY PROCEDURE

32

ASSEMBLY PROCEDURE

33

STYLIZED STARTER (OHV 13.5 -17)

34

ASSEMBLY

34

CHAPTER 6 ELECTRICAL SYSTEMS

35

GENERAL INFORMATION

35

OPERATION

35

STARTING CIRCUIT AND ELECTRIC STARTERS

35

CHARGING CIRCUIT

35

CONVERTING ALTERNATING CURRENT TO

 

DIRECT CURRENT

36

HALF WAVE RECTIFIER SINGLE DIODE

36

FULL WAVE RECTIFIER BRIDGE RECTIFIER

36

COMPONENTS

36

BATTERY

36

WIRING

36

ELECTRICAL TERMS

37

BASIC CHECKS

37

TROUBLESHOOTING ELECTRICAL STARTER

 

CIRCUIT FLOW CHART

38

TROUBLESHOOTING ELECTRICAL CHARGING

 

CIRCUIT FLOW CHART

39

Tecumseh Products Company

i

ii

CHAPTER 1 GENERAL INFORMATION

ENGINE IDENTIFICATION

Tecumseh engine model, specification, and serial numbers or date of manufacture (D.O.M.) are stamped into the blower housing, or located on a decal on the engine in locations as illustrated (diag. 1 & 2). The engine identification decal also provides the applicable warranty code and oil recommendations (diag. 2).

Interpretation of Model Number

The letter designations in a model number indicate the basic type of engine.

OHH

-

Overhead Valve Horizontal

OHM

-

Overhead Valve Horizontal

 

 

MediumFrame

OHSK

- Overhead Valve Horizontal Snow King

OVM

- Overhead Valve Vertical Medium Frame

OVRM

- Overhead Valve Vertical Rotary Mower

OVXL

- Overhead Valve Vertical Medium Frame

 

 

Extra Life

OHV

-

Overhead Valve Vertical

The number designations following the letters indicate the basic engine model.

The number following the model number is the specification number. The last three numbers of the specification number indicate a variation to the basic engine specification.

The serial number or D.O.M. indicates the production date of the engine.

Using model OHV16-204207A, serial 5215C as an example, interpretation is as follows:

OHV16-204207A is the model and specification number.

OHV Overhead Valve Vertical

16Indicates the basic engine model.

204207A is the specification number used for properly identifying the parts of the engine.

5215C is the serial number or D.O.M. (Date of Manufacture)

5 is the last digit in the year of manufacture (1995).

215indicates the calendar day of that year (215th day or August 3, 1995).

C represents the line and shift on which the engine was built at the factory.

Emissionized engines that meet the California Air Resource Board (C.A.R.B.) or the Environmental Protection Agency (E.P.A.) standards will include additional required engine information on the engine decal.

NOTE: To maintain best possible emission performance, use only Genuine Tecumseh Parts.

ENGINE MODEL

NUMBER

1

THIS ENGINE MEETS 1995-1998

CALIF. EMISSION REGULATIONS FOR

ULGE ENGINES AS APPLICABLE

FUEL: REGULAR UNLEADED OIL : USE SAE 30

OHV 125 203000A

(D)

RTP358UIG2RA

 

358cc

3057D

2

1

SHORT BLOCKS

New short blocks are identified by a tag marked S.B.H. (Short Block Horizontal) or S.B.V. (Short Block Vertical). Original model identification numbers of an engine should always be transferred to a new short block for correct parts identification (diag. 3).

THIS SYMBOL POINTS OUT IMPORTANT SAFETY INSTRUCTIONS WHICH IF NOT FOLLOWED COULD ENDANGER THE PERSONAL SAFETY OF YOURSELF AND OTHERS. FOLLOW ALL INSTRUCTIONS.

FUELS

SBV OR SBH IDENTIFICATION NUMBER

SHORT BLOCK IDENTIFICATION TAG

SBV- 564A

SER 5107

SERIAL NUMBER

3

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, or 15% MTBE, or 15% ETBE may also be used.

Leaded fuel is generally 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.

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. This time may be extended with the use of a fuel stabilizer like TECUMSEH'S, part number 730245.

See "STORAGE" instructions in the Technician's Manual, Operators Manual, or Bulletin 111.

ENGINE OIL

TECUMSEH FOUR CYCLE ENGINES REQUIRE THE USE OF A 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 SAE10W40 OIL.

FOR SUMMER (Above 320 F) (0oC) USE SAE30 OIL. PART #730225

Use SAE30 oil in high temperature, high load applications. Using multigrade oil may increase oil consumption. FOR WINTER (Below 320F) (0oC) USE SAE5W30 OIL. PART #730226

(SAE 10W is an acceptable substitute.)

(BELOW 00F (-18oC) ONLY): SAE 0W30 is an acceptable substitute.

NOTE: For severe, prolonged winter operation of HH120 model, SAE10W oil is recommended.

Capacities

Engine Model

 

Oz.

 

ml.

OHH,OHSK 50-70

21

630

OVRM 40 - 6.75

21

630

OVRM105 & 120

21

630

OHSK80 - 100

 

26

720

OHM, OHSK 110* - 130

32

960

OVM 120, OVXL 120, 125

32

960

OHV 11 - 13 without oil filter

32

960

OHV 11 - 13 with filter

39

1170

OHV 13.5

- 17

without oil filter

55

1650

OHV 13.5

-17

2 1/4" filter (part # 36563)

62

1860

OHV 13.5

-17

2 5/8" filter (part # 36262)

64

1920

* NOTE: Model OHSK110 with a spec. of 221000 and up, have a capacity of 26 oz. (720 ml.)

2

Oil Change Intervals: Change the oil after the first two (2) hours of operation and every 25 hours thereafter (OHH & OHSK50-130, OHV13.5-17 every 50 hours), or more often if operated under dusty or dirty conditions. If the engine is run less than 25 hours per year, change the oil at least once per year.

NOTE: The oil filter (if equipped) requires changing every 100 hours or more often if operated under dusty or dirty conditions.

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.

CAUTION: Remove the spark plug wire before doing any service work on the engine.

Oil Change Procedure: Locate the oil drain plug. On some units this plug is located below the deck through the bottom of the mounting flange. Other units drain at the base of the engine above the deck or frame. On some rotary mower applications, where access to the drain plug is restricted by the equipment, it may be necessary to drain the oil by tipping the mower in a position that would allow the oil to drain out of the fill tube.

On units that the drain plug is accessible, remove the plug and allow the oil to drain into a proper receptacle. Always make sure that drain oil is 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.

TUNE-UP PROCEDURE:

NOTE: Today's fuels can cause many problems in an engines performance due to the fuels quality and short shelf life. Always check fuel as a primary cause of poor engine performance.

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.

STANDARD

OHV

 

CAUTION: Remove the spark plug wire

PLUG

 

 

 

 

 

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 and

 

 

 

change or add oil as required.

 

 

3.

Remove the blower housing and clean all dirt,

 

 

 

grass or debris from the intake screen, head,

 

 

 

cylinder cooling fins, carburetor, governor

 

 

 

levers and linkage.

 

 

4.

Make sure the fuel tank, fuel filter and fuel

 

4

 

line are clean. Replace any worn or damaged

 

 

 

 

governor springs or linkage. Make the proper governor adjustments and carburetor presets where required.

5.When replacing the spark plug, consult the proper parts breakdown for the spark plug to be used in the engine being serviced. Set the proper spark plug gap (.030") (.762 mm) and install the spark plug in the engine. Tighten the spark plug to 21 foot pounds (28 Nm) of torque. If a torque wrench isn’t available, screw the spark plug in as far as possible by hand, and use a spark plug wrench to turn the spark plug 1/8 to 1/4 turn further if using the old spark plug, or 1/2 turn further if using a new spark plug.

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.Properly reinstall the blower housing, gas tank, fuel line, and air cleaner assembly if removed.

8.Make sure all remote cables are properly adjusted for proper operation. See Chapter 4 under "Speed Controls and Linkage".

9.Reinstall the spark plug wire, add fuel and oil as necessary, start the engine.

3

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's 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 stabilizer to allow it to reach the carburetor.

Draining the Fuel System

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 all gasoline from the fuel tank by running the engine until the engine stops, or by draining the fuel tank by removing the fuel line at the carburetor or fuel tank. Be careful not to damage the fuel line, fittings, or fuel tank.

2.Drain the carburetor by pressing upward on bowl drain (if equipped) which is located on the bottom of the carburetor bowl. On carburetors without a bowl drain, the carburetor may be drained by loosening the bowl nut on the bottom carburetor one full turn. Allow to completely drain and retighten the bowl nut being careful not to damage the bowl gasket when tightening.

3.If "Gasohol" has been used, complete the above procedure and then put one half pint of unleaded gasoline into the fuel tank and repeat the above procedure. If Gasohol is allowed to remain in the fuel system during storage, the alcohol content can cause rubber gaskets and seals to deteriorate.

Change Oil: If the oil has not been changed recently, this is a good time to do it. See "Oil Change Procedure" on page 3.

Oil Cylinder Bore

1.Disconnect the spark plug wire and ground the spark plug wire to the engine. Remove the spark plug and put a 1/2 ounce (15 ml.) of clean engine oil into spark plug hole.

2.Cover the spark plug hole with a shop towel.

3.Crank the engine over, slowly, several times.

4.Install the spark plug and connect the spark plug wire.

Clean Engine: Remove the blower housing and clean all dirt, grass or debris from the intake screen, head, cylinder cooling fins, carburetor, governor levers and linkage.

4

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 the life of the engine.

Tecumseh engines use either a polyurethane or a paper-type air filter system. A polyurethane pre- cleaner or a flocked screen may be used with the main filter. Snow King® engines do not use an air filter due to the clean operating environment and to prevent filter freeze-up.

Extremely dirty conditions may require more frequent filter cleaning or replacement.

COVER

KLEEN-AIRE®

 

ENTRANCE FROM

FOAM

UNDER BLOWER

ELEMENT

HOUSING

 

OPERATION

The air cleaner cover allows access to the air filter element(s) and prevents large particles from entering the filter body. Air is filtered through the pre-cleaner or flocked screen if equipped, and the polyurethane or paper filter element. Pre-cleaners or flocked screens provide more air cleaning capacity.

In Tecumseh's Kleen Aire® system, air is drawn in through a rotating screen or recoil housing to be centrifugally cleaned by the flywheel before the air enters the air filter.

COMPONENTS

The cover holds the filter element and prevents large debris from entering the filter body.

The polyurethane wrap pre-cleaner is used on XL or XL/C engine models with paper filter elements.

The paper or polyurethane filter element is the main filter to trap dust and dirt. Dry-type paper elements are pleated paper for increased surface area and rubberized sealing edges. The polyurethane filter uses an oil film to trap fine particles found in dust.

AIR CLEANER BODY

FLOCKED SCREEN

1

COVER

POLYURETHENE

WRAP

PAPER

ELEMENT

AIR CLEANER

BODY

The flocked screen is used as an additional filter on XL or XL/C engine models that use a polyurethane filter element.

KLEEN-AIRE® ENTRANCE FROM UNDER BLOWER HOUSING

2

5

TROUBLESHOOTING OR TESTING

If the engine's performance is unsatisfactory (needs excessive carburetor adjustments, starts smoking abnormally, loses power), the first engine component to be checked is the air filter. A dirt restricted or an oil soaked filter will cause noticeable performance problems. A polyurethane filter may be cleaned following the service procedure listed under "Service" in this chapter. A paper-type air filter should only be replaced. A paper-type filter cannot have an oil film present on the paper. Follow the procedure listed in the "Service" section of this chapter for filter replacement or cleaning.

SERVICE

Service on the polyurethane filter element (cleaning and oiling) is recommended every three (3) months or every twenty five (25) operating hours, whichever comes first. Extremely dirty or dusty conditions may require daily cleanings.

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 THE PROPER TECUMSEH ORIGINAL REPLACEMENT PART.

DISASSEMBLY PROCEDURE

1.Unlock the tabs or remove the screws or wing nuts holding the air cleaner cover in place.

2.Remove the hex nuts holding the element down if equipped. New nuts are supplied with a new filter and are to be used for proper sealing.

3.Clean the excess contaminants out of the air cleaner body before removing the old element.

4.Remove the old element and the polyurethane pre-cleaner if equipped.

5.On air cleaners that use a flocked screen under the polyurethane element, remove the air cleaner assembly from the carburetor before removing the flocked screen. This prevents dirt from entering the carburetor (diag 3).

6.Clean the inside of the cover and body, remove the old gasket between the carburetor and the air cleaner assembly.

7.Reinstall the air cleaner assembly using a new gasket.

8.Use reverse procedure for reassembly. When installing the polyurethane pre-cleaner, make sure the seam is installed to the outside to prevent gaps between the paper element and the pre-cleaner.

WING NUTS

 

 

 

 

 

 

 

 

COVER

 

 

 

 

 

 

 

GASKET

FILTER A

 

 

 

 

 

 

NUTS

 

 

 

 

 

 

(FOAM)

 

 

 

 

 

 

 

 

KLEEN-AIRE®

 

 

 

 

 

 

FILTER B

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ENTRANCE

 

 

 

 

 

 

 

BODY

COVER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GASKET

FOAM

 

 

 

 

 

 

 

 

FILTER

 

 

 

 

 

 

 

 

KLEEN-AIRE®

 

 

 

FLOCKED SCREEN

 

 

 

 

 

 

 

 

 

 

 

ENTRANCE

 

 

 

 

 

 

 

 

GASKET3

6

Polyurethane-Type Filter Element or pre-cleaner

This type of air filter or pre-cleaner can be serviced when restricted with dust or dirt. Wash the filter or pre- cleaner in a detergent and water solution until all the dirt is removed. Rinse in clear water to remove the detergent solution. Squeeze the filter or pre-cleaner (do not twist) to remove the excess water. Wrap the filter or pre-cleaner in a clean cloth and squeeze it (do not twist) until completely dry.

On the polyurethane filter only, re-oil the filter by applying engine oil and squeezing it vigorously to distribute the oil. Roll the filter in a cloth and squeeze it (do not twist) to remove the excess oil. The pre-cleaner must not be oiled.

Clean the air cleaner housing and cover being careful not to allow dirt to fall into the carburetor or intake pipe.

Paper -type filter element

Paper type air filter elements can only be serviced by replacement. Do not attempt to clean a paper filter element. Replacement filters are available at any authorized Tecumseh Service Outlet. Be sure to use new filter nuts or seals for the air cleaner studs if supplied with the new filter (diag. 5).

Flocked Screen

A flocked screen may be cleaned by blowing compressed air through the screen from the backside. If the screen cannot be cleaned with this procedure, it should be replaced with a new screen.

COVER

KLEEN-AIRE®

 

ENTRANCE FROM

FOAM

UNDER BLOWER

ELEMENT

HOUSING

 

COVER

POLYURETHENE WRAP

PAPER

ELEMENT

AIR CLEANER BODY

AIR CLEANER BODY

FLOCKED SCREEN

4

KLEEN-AIRE® ENTRANCE FROM UNDER BLOWER HOUSING

5

7

CHAPTER 3 CARBURETORS AND FUEL SYSTEMS

GENERAL INFORMATION

Tecumseh overhead valve engines use float type carburetors. Float type carburetors use a hollow float to maintain the operating level of fuel in the carburetor.

The float type carburetor will have a fuel enrichment system of either a primer or a manual choke to provide easy cold engine starting. The carburetor fuel mixtures are either fully adjustable, partially adjustable, or nonadjustable. Carburetor adjustments, cleaning, and related fuel system service is covered in this chapter.

Some Tecumseh engines utilize Walbro carburetors. Basic operation is very similar to the Tecumseh float style carburetor.

Carburetors used by Tecumseh can be identified by a manufacturing number stamping on the carburetor as

illustrated (diag. 1).

When servicing carburetors, use the engine model and specification number to obtain the correct carburetor part number. An alternate method to find the correct carburetor part number is to use the manufacturing number stamped on the carburetor and convert this number to a service part number. In the carburetor section of the Master Parts Manual or Microfiche Catalog, a cross reference chart will convert a carburetor manufacturing number to a Tecumseh Service part number.

Complete carburetor replacement may be accomplished by a standard service carburetor. A standard service carburetor is a basic carburetor that may require the use of original carburetor parts or additional new parts to adapt to the specification. An instruction sheet is provided with the new service carburetor or see “SERVICE” in this chapter.

ALTERNATE LOCATION

FOR MANUFACTURING

NUMBER

89 4F5

 

89

4F5

 

 

 

 

MANUFACTURING

 

CARBURETOR

1

NUMBER

 

DATE CODE

OPERATION

In the “CHOKE” or “START” position, the choke

 

shutter is closed, and the only air entering the engine

 

enters through openings around the shutter. As the

CHOKE PLATE

starting device is operated to start the engine,

downward piston travel creates a low air pressure area

 

in the engine cylinder above the piston. Higher

 

pressure (atmospheric air) rushes into the engine to

 

fill the created low pressure area. Since the majority

 

of the air passage is blocked by the choke shutter, a

 

relatively small quantity of air enters the carburetor

 

at increased speed. The main nozzle and both idle

 

fuel discharge ports are supplying fuel due to the low

 

air pressure in the intake of the engine. A maximum

 

fuel flow through the carburetor orifices combined with

 

the reduced quantity of air that passes through the

 

carburetor, make a very rich fuel mixture which is

FLAT

needed to start a cold engine.

DOWN

At engine IDLE speed, a relatively small amount of

2

fuel is required to operate the engine. The throttle is

 

almost completely closed. A fuel / air mixture is supplied through the primary idle-fuel discharge orifice during idle.

During INTERMEDIATE engine operation, a second orifice is uncovered as the throttle shutter opens, and more fuel mixture is allowed to atomize with the air flowing into the engine.

During HIGH SPEED engine operation, the throttle shutter is opened. Air flows through the carburetor at high speed. The venturi, which decreases the size of the air passage through the carburetor, further accelerates the air flow. This high speed movement of the air decreases the air pressure at the main nozzle opening. Fuel is forced out the main nozzle opening due the difference in the atmospheric air pressure on the fuel in the carburetor bowl and the reduced air pressure at the main nozzle opening.

8

For the fuel to flow, the carburetor bowl must be either vented externally or internally. Some internally vented float style carburetors use a tygon tube and a vent within the air intake. This tube must be present for the carburetor to operate properly (diag. 3).

Air is bled into the main nozzle through the air bleed located in the air horn. This mixes fuel and air prior to the fuel leaving the main nozzle. Atomization occurs as the fuel mixture contacts the fast moving air stream and the mist flows into the intake of the engine.

TYGON TUBE

INTERNAL VENT

EXTERNAL VENT 3

FUEL PRIMERS

Primers may be mounted remotely or as an integral part of the carburetor. The basic function of the primer is to supply an air pressure charge to the carburetor main well or carburetor bowl to displace fuel directly into the carburetor venturi. This displaced fuel provides a rich mixture necessary for engines to start easily on the first or second attempt (diag. 4 & 5).

Primers must be vented either internally through a passage in the carburetor air horn prior to the venturi or externally through a hole in the primer bulb. The vent allows atmospheric air to enter the fuel bowl during operation and to fill the primer bulb after the primer bulb is released.

PRIMER BULB

VENT

4

PRIMER BULB

MAIN NOZZLE

MAIN JET

5

IMPULSE FUEL PUMPS

Impulse fuel pumps may either be mounted externally onto the carburetor fuel inlet or remotely mounted. This pump is connected in the fuel line between the fuel supply and the carburetor or directly to the fuel inlet.

Impulse fuel pumps are operated by crankcase impulses 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 impulses to the pump diaphragm. The impulses actuate the diaphragm and flap valves to lift the fuel from the fuel tank to the carburetor (diag. 6). A crankcase overfilled with engine oil can affect pump operation.

FLOAT STYLE CARBURETORS

A float is used to maintain the operating level of fuel in the carburetor bowl. As the fuel is used by the engine, 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. Fuel flows by gravity or a pulse pump into the fuel bowl. As the fuel level in the bowl again rises, it raises 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 and the fuel level in the carburetor bowl remains constant (diag. 7). The float height is set according to the service procedure.

CARBURETOR

FITTING

 

VALVE CLOSED

 

VALVE OPEN

 

 

 

ATMOSPHERIC

 

 

 

 

 

DIAPHRAGM

 

 

VENT

 

 

 

 

 

 

 

 

 

 

FILTER

 

 

 

 

 

AIR BLEED

 

VALVE OPEN

 

VALVE CLOSED

 

 

 

 

 

FUEL SUPPLY

 

PULSE LINE

 

 

 

 

TO CRANKCASE

êCRANKCASE PRESSURE

êCRANKCASE SUCTION AND

á SUCTION FUEL FLOW DIRECTION

áATMOSPHERIC PRESSURE ACTING

FLOW DIRECTION

 

ATMOSPHERIC PRESSURE

 

á

ON DAMPING DIAPHRAGM

ATMOSPHERIC PRESSURE

êCAUSED FUEL FLOW

6

FUEL FLOW

ACTING ON DAMPING

 

 

 

á DIAPHRAGM

 

 

 

 

 

 

 

 

 

IDLE AIR

MAIN AIR

 

 

 

BLEED

 

 

 

 

 

BLEED

 

 

 

 

 

 

 

 

 

 

CHOKE

 

 

 

 

 

SHUTTER

 

 

THROTTLE

 

 

 

 

 

SHUTTER

 

 

 

 

 

 

 

 

INLET NEEDLE

IDLE

 

 

AND SEAT

 

 

 

 

 

ADJUSTMENT

 

 

 

 

 

 

 

 

FLOAT

 

 

MAIN NOZZLE

MAIN

 

 

7

 

 

ADJUSTMENT

9

CARBURETOR VISUAL IDENTIFICATION

Series1 Carburetors

Series 1 carburetors are used on some 4 - 7 model overhead valve engines. This float style carburetor has a smaller venturi than the Series 3 or 4 carburetor and has no bosses on each side of the idle mixture screw. The main and idle mixture may be fixed or adjustable. A remote primer or choke may also be used with this carburetor (diag. 8).

Series 3 & Series 4 Carburetors

Series 3 or 4 carburetors are generally used on 8 through 14 model 4-cycle engines. The quickest way to identify these carburetors is by the presence of bosses on each side of the idle mixture screw (diag. 9).

To determine whether the carburetor is a Series 3 or Series 4, look at the throttle end of the carburetor. Series 3 will have one throttle plate screw (diag. 10). The Series 4 will have two throttle plate screws (diag. 11).

Series 6 Carburetors

Series 6 carburetors are used on 2 and 4-cycle engines in the 3 to 6 model range. Series 6 uses a simple fixed idle and fixed main fuel circuit. Series 6 carburetors are commonly used on rotary mower applications. Series 6 are nonadjustable, with a stepped primer bulb and a bowl prime system (diag. 12).

Series 7

Series 7 carburetors are totally nonadjustable. The die cast carburetor body is similar in appearance and slightly longer than the Walbro LMK body. The choke shaft is made of a plastic material with an internal slot to hold the choke shutter. The carburetor base is flat to accept a Vector style bowl that is held on with a wire bail. (diag. 13)

9

8

10

11

12

13

10

Series 8

Series 8 carburetors have both a fixed main and a fixed idle circuit. These carburetors are totally nonadjustable. This series of carburetor uses an integral primer system like the Series 6. Distinguish this carburetor from the Series 6 by the fixed idle jet that appears as a screw just above the bowl on the primer side. This fixed idle jet may also be capped. (diag. 14)

CAPPED FIXED

IDLE JET

CAP

14

Series 9

Series 9 carburetors are hybrid versions of the Series 8. This carburetor uses a fixed idle jet and fixed main fuel circuit. This carburetor is totally nonadjustable. The bowl nut uses a ball plug on the bottom to cover the center drilling. Also visible is a plastic main fuel discharge nozzle in the venturi. The Idle mixing well and jet will be visible but not machined (diag. 15)

Series 10

This carburetor is for use on all season engine applications. It is the equivalent of the series "8" with the addition of a choke. It has a fixed main and idle with a serviceable main nozzle and a primer assist, with the added benefit of a choke for cold weather starting.

MIXING WELL

CAST BUT NOT

MACHINED

IDLE JET

CAST BUT NOT

MACHINED

15

CHOKE PLATE

FLAT SIDE DOWN

15

Walbro Model LMK

OHV 15-17 models use this float-feed carburetor. The carburetor is attached to the intake pipe using studs that also fasten the air filter body. Walbro model and manufacturing numbers are found on the throttle end of the carburetor. This carburetor has a fixed, nonadjustable main mixture jet.

Idle mixture screws were adjustable on early production OHV15. This has since changed to a fixed idle jet which may be capped for tamper resistance.

If no spring is visible, the jet is fixed. Servicing should be done by a Authorized Tecumseh Dealer.

LOW IDLE

 

MIXTURE SCREW

16

MAY BE ADJUSTABLE OR FIXED

 

 

11

TESTING

1.After 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 and removing the spark plug. Install a commercially available spark tester and check for spark. If the spark is bright blue and consistent, proceed to step 2. If no or irregular spark see Chapter 8 under "Testing".

2.Visually inspect the removed spark plug for a wet condition indicating the presence of gasoline in the

cylinder.

NOTE: Check plug for correct reach (diag. 17).

3.If the spark plug is dry, check for restrictions in the fuel system before the carburetor. If the spark plug is wet, continue with step # 7.

CHECK THE FUEL CAP FOR PROPER VENTING. With a proper draining receptacle, remove the fuel line clamp on the carburetor fuel inlet and pull the fuel line off the fitting. Examine the fuel flow with the fuel cap both on and off the fuel tank.

CAUTION: DRAIN THE FUEL INTO AN

STANDARD

OHV

PLUG

 

17

APPROVED CONTAINER OUTDOORS, AND AWAY FROM ANY OPEN FLAME OR COMBUSTION SOURCE. BE SURE THE ENGINE IS COOL.

NOTE: Todays fuels can cause many problems in an engines performance, due to the fuels quality and short shelf life. Always check fuel as a primary cause of engine performance.

4.Remove the air filter, heater box, or air cleaner assembly if applicable to visually check that the choke shutter completely closes or check to see if fuel comes out of the main nozzle during priming.

5.If the fuel flow from the tank is adequate and no fuel is evident during priming, the carburetor will need to be removed for service. See “Service” in this chapter or consult the “Carburetion Troubleshooting” chart to diagnose carburetor symptoms. Improper fuel flow indicates the fuel, fuel line, filter or tank require cleaning or replacement.

6.Check the engine compression using a commercially available compression tester and follow the tester’s recommended procedure. Low compression, a dry spark plug, adequate fuel flow, and a known good functional carburetor indicates an internal engine problem exists. See Chapter 9 under “Troubleshooting.”

7.A wet spark plug indicates fuel is being supplied by the carburetor. The engine may be flooded by a restricted air filter, carbon shorted or defective spark plug, excessive choking or over priming, improperly adjusted or defective carburetor. With the spark plug removed and a shop towel over the spark plug hole, turn the engine over slowly 3 or 4 times 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.

8.Replace the air filter if restricted or oil soaked. Replace the spark plug if questionable. Install the spark plug and high tension lead and try to start the engine.

9.If the engine floods and fails to start, the carburetor will require service. See the proceeding “Carburetion Troubleshooting” chart for additional causes. If the carburetor is functioning properly the problem may be ignition timing related. See Chapter 8 “Ignition” under “Troubleshooting.”

SERVICE

Carburetor Pre-sets and Adjustments

Before adjusting any mixture screws the necessary carburetor presets should be made. Check for the proper governor adjustments as outlined in Chapter 4. Identify the correct carburetor model and manufacturer to find locations of the high and low speed adjustment screws. Check the throttle control bracket for proper adjustment allowing a full choke shutter position. See Chapter 4 under "Speed Controls and Linkage". Check to see if the normal maintenance procedures have been performed (oil changed, fresh fuel, air filter replaced or clean). Consult microfiche card #30 to find the correct R.P.M. settings for the engine. Start the engine and allow it to warm to operating temperature. The carburetor can now be adjusted.

NOTE: RPM SETTINGS CAN ALSO BE FOUND ON THE COMPUTERIZED PARTS LOOK UP SYSTEMS.

12

Pre-sets and Adjustments (Tecumseh and Walbro carburetors)

Turn both the main and idle mixture adjusting screws in (clockwise) until finger tight if applicable.

NOTE: OVERTIGHTENING WILL DAMAGE THE TAPERED PORTION OF THE NEEDLE.

Now back the mixture screws out (counterclockwise) to obtain the pre-set figure in the chart shown.

NOTE: SOME CARBURETORS HAVE FIXED IDLE AND MAIN JETS. IDENTIFY THE SERIES OF CARBURETOR USING THE VISUAL IDENTI- FICATION IN THIS CHAPTER. IDLE MIXTURE FIXED JETS APPEAR AS ADJUSTING SCREWS WITHOUT TENSION SPRINGS AND ARE NOT ADJUSTABLE.

Final Adjustments

Tecumseh Carburetors

Engine Model

Main Pre-set

Idle Pre-set

 

 

 

 

All models with

 

 

float-type carburetors

1-1/2 turn

1 turn

 

 

 

 

All models with

 

 

diaphragm-type

 

 

carburetors

1 turn

1 turn

 

 

 

 

Walbro Carburetors

 

 

 

 

 

Carburetor Model

 

 

 

LMK

 

Fixed

1 turn if

 

 

 

adjustable

 

 

 

or seated,

 

 

 

if fixed

 

 

 

 

Start the engine and allow it to warm up to normal operating temperature (3 - 5 minutes). Set the speed control to the HIGH or FAST position, then turn the main mixture adjustment screw in (clockwise) slowly until the engine begins to run erratic. Note the position of the screw. Now, turn the screw out (counterclockwise) until the engine begins to run erratic. Turn the screw in (clockwise) midway between these two positions. This will be the best setting.

Set the speed control to the IDLE or SLOW position. Adjust the idle mixture screw following the same procedure used to adjust the main mixture adjustment screw.

Identify the location of both HIGH and LOW speed adjustments, then locate the recommended HIGH and LOW R.P.M. setting according to microfiche card # 30 and adjust the engine speed accordingly.

NOTE: RPM SETTINGS CAN ALSO BE FOUND ON THE COMPUTERIZED PARTS LOOK UP SYSTEMS.

TECUMSEH CARBURETORS

DUAL SYSTEM / SERIES "6"

SERIES "7"

SERIES "3" & "4"

 

 

 

 

 

 

MAIN

 

 

 

 

IDLE MIXTURE

 

MIXTURE

NON-ADJUSTABLE

 

FIXED HIGH AND LOW SPEED

 

 

SCREW

18

19

SCREW

 

PRIMER NO CHOKE

20

MIXTURE

 

WALBRO

CARBURETOR

SERIES "8"

CAPPED

FIXED

IDLE JET

NON-ADJUSTABLE

(ADJUSTABLE MAIN FOR

EXPORT)21

SERIES "9"

NON-ADJUSTABLE

 

SERIES "10"

22

23

WALBRO LMK

24

13

If further adjustment is required, the main adjustment should be made under a load condition.

If the engine stops or hesitates while engaging the load (lean), turn the main mixture adjusting screw out (counterclockwise) 1/8 turn at a time, testing each setting with the equipment under load, until this condition is corrected. A few Tecumseh carburetors were built as air adjust idle system. If you have one, the adjustments are reversed out for lean in for richer.

If the engine smokes excessively (rich), turn the main adjusting screw in (clockwise) 1/8 turn at a time, testing each setting with the equipment under load, until this condition is corrected.

After the main mixture screw is set, move the speed control to the IDLE or SLOW position. If the engine does not idle smoothly, turn the idle mixture screw 1/8 turn either in (clockwise) or out (counterclockwise) until engine idles smoothly.

Recheck the high and low R.P.M. setting and adjust as necessary.

CARBURETOR DISASSEMBLY PROCEDURE

NOTE : CARBURETORS THAT ARE EMISSION COMPLIANT (MANUFACTURING NUMBERS 5000 OR GREATER) WITH FIXED IDLE OR MAIN JETS ARE TO BE REMOVED BY DEALERS ONLY FOR INSPECTION AND CLEANING.

1.Note or mark the high and low mixture adjusting screws to aid in reassembly (if applicable). Remove the high speed mixture screw, bowl nut, and float bowl. Remove the idle mixture screw assembly. On Series 7 carburetors, release the wire retainer that retains the bowl and remove the bowl assembly. If a screwdriver or similar tool is used to release the retainer, carefully move the retainer to prevent bending of the wire.

2.Series 8 carburetors have a tamper resistant cap, over the fixed idle jet. (diag. 21). The cap is removed by piercing it with an ice pick or similar instrument, then remove the jet for service, always replace the cap.

3.Note the position of the spring clip on the inlet needle and float. Remove the float hinge pin with a needlenose pliers. Some carburetors use a float dampening spring to aid the inlet valve to maintain a steady position in rough service applications. Note the position of the hooks before removing the float hinge pin (diag. 25). On Series 7 carburetors, grasp the crossbrace on the float with a needlenose pliers and pull straight out to release the float hinge pin.

4.Remove the float, clip, and inlet needle.

5.Remove the inlet needle seat using a wire or a paper clip with a 3/32" (2.38 mm) hook end (Tecumseh carburetors only, Walbro model LMK uses a non-serviceable seat). Push the hook through the hole in the center of the seat and pull out to remove it.

6.On Series 7 only, remove the main nozzle tube, "O" ring, and spring located in the center leg of the carburetor bowl. Remove the bowl drain screw and gasket. Remove the spring, metering jet, and "O" ring.

7.Note or mark the action of the choke and throttle shutters and the hook points of the choke or throttle return spring or seal retainer springs located on the top of the choke or throttle shaft.

NOTE: MARK THE EDGES OF THE THROTTLE AND CHOKE SHUTTERS PRIOR TO DISASSEMBLY. THE SHUTTERS HAVE BEVELED EDGES AND MUST BE INSTALLED IN THE ORIGINAL POSITION.

Remove the throttle shutter, throttle shaft, choke shutter, springs and choke shaft by removing the screw or screws that attach the throttle or choke shutter to the shaft inside the air horn. To remove the choke shaft assembly on Series 7 or Walbro LMK carburetors, grasp the choke shutter with a pliers and pull it through the slot in the choke shaft. Slide the choke shaft out of the carburetor body.

LONG END

 

 

 

 

 

CLIP

 

 

 

 

 

 

 

 

 

 

OPEN END

OF CLIP

 

 

 

 

 

 

 

 

OF CLIP

 

 

 

 

 

 

 

 

 

 

 

 

THROTTLE

 

 

 

 

 

 

END

CHOKE

 

 

 

 

 

END

25

3/32" (2.38 mm)

26

27

14

8. Remove the primer bulb (if equipped) by

 

 

 

 

grasping with a pliers and pulling and twisting

 

 

out of the body. Remove the retainer by prying

 

 

and lifting out with a screwdriver. Do not re-

 

 

use old bulb or retainer (diag. 28).

 

 

9. Remove all welch plugs if cleaning the

 

 

carburetor. 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

 

28

to pry the plug out of the hole (diag. 29).

 

 

 

NOTE: DO NOT REMOVE ANY BALL OR CUP PLUGS (diag. 29).

 

10.Note the direction of the inlet fitting. If necessary the inlet fitting can be removed by pulling with a pliers or vise, do not twist. The fitting must be replaced. Tap a 1/4-20 thread inside the metal shank, use 1/4"-20 bolt and nut inserted into a 1/4" (6.350 mm) flat washer and 1/2" (12.700 mm) nut, thread the bolt into the shank, and thread the nut down to pull out the shank.

11.The Walbro LMK carburetor main fuel jet can be removed only if the jet is damaged or if a high altitude jet is needed to be installed. To remove place the carburetor firmly in a soft jawed vice. Using a punch the same size or slightly smaller than the jet, drive the jet through and into the center leg. Insert the high altitude jet in the same hole. Using a punch slightly larger than the diameter of the new jet, tap it into place flush with the outside of the center leg casting (diag. 31).

SMALL

PIERCE PLUG

 

CHISEL

 

PRY OUT

WITH TIP

 

 

 

WELCH PLUG TO

 

 

PLUG

 

 

 

 

BE REMOVED

 

 

 

DO NOT ALLOW

 

 

 

 

 

 

 

 

CHISEL POINT

 

 

 

ABOUT 1/8"

TO STRIKE

 

 

 

(3.175 mm)

CARBURETOR

 

 

 

WIDE

BODY OR

 

 

 

 

CHANNEL

 

 

 

 

SMALL CHISEL

29

REDUCER

DO NOT REMOVE PLUGS

BRASS OR BALL PLUG

BALL PLUG IDLE FUEL PASSAGE REDUCTION ROD INSIDE 30

WALBRO LMK SERIES ATMOSPHERIC

VENT

HIGH SPEED JET

31

Impulse Fuel Pump

The valve type impulse pump can be serviced using the following procedure.

1.Remove the old filter on the back of the pump body if applicable.

2.Note or mark the pump body alignment, remove the four screws and disassemble the pump.

3.Remove the gaskets, diaphragms, old valves and spring bearing from the spring.

4.Clean the body parts with solvent.

5.Install new valves with the face of the valve facing the raised portion of the passage. After installation, cut off the extended portion of the valves.

6.Install the diaphragms against the center portion of the body with the gaskets against the outside covers. The parts can only can be assembled one way without damage.

7.Install the spring bearing on the new spring and place into position.

8.Assemble the body sections, install the retaining screws, and torque the screws to 12 - 16 inch pounds (1.36 - 1.81 Nm).

9.Install new filter in pump cavity if applicable.

 

 

11

 

 

1

 

 

10

 

 

 

4

 

 

 

7

 

 

11

 

5

 

 

2

 

 

 

 

8

1

- Body, Impluse

6

2

- Body, Pump

 

 

 

3

- Cover, Pump

 

 

 

4

- Bearing, Spring

 

 

 

5

- *Valve, Check (2)

3

6

- *Gasket, Pump Cover

 

 

 

7

- *Diaphragm, Pump (2)

9

 

 

9

- Screw, 1-1/4" (4)

 

 

10 - *Spring, Pressure

 

11 - *Filter, Air

32

 

15

FLOAT ADJUSTING PROCEDURE

All Tecumseh carburetors with an adjustable float require the correct float height to achieve the proper operation and easy engine starts. To check the float setting, hold the carburetor in an upside down position. Remove the bowl nut, float bowl, and "O" ring. Place an 11/64" (4.36mm) diameter drill bit across the top of the carburetor casting on the opposite side and parallel to the float hinge pin. The float must just touch the drill bit when the bit is flush with the edge of the float. If the float is too high or too low, adjust the height by bending the tab accordingly. If the required adjustment is minor, the tab adjustment may be made without removing the float and carefully inserting a small bladed screwdriver to bend the tab.

FLOAT

FLOAT HINGE

AND AXLE

FLOAT

SETTING

11 / 64" (4.36 mm)

ADJUSTING TAB

INLET NEEDLE

33

 

AND SEAT

If float sticking occurs due to deposits, or when the fuel tank is filled for the first time, this condition can be quickly corrected by loosening the carburetor bowl nut one full turn. Turn the bowl 1/4 inch in either direction, then return the bowl to its original position and tighten the bowl nut.

THE TECUMSEH SERIES 7 AND THE WALBRO MODEL LMK CARBURETOR HAVE A FIXED AND NONADJUSTABLE FLOAT HEIGHT.

Inspection

After careful disassembly of the carburetor and the removal of all non metallic parts, all metallic parts should be cleaned with solvent, or commercial carburetor cleaner, no longer than 30 minutes. Wearing eye protection, use compressed air and soft tag wire or monofilament fishing line to clean internal carburetor passages. To perform a proper carburetor rebuild, the welch plugs must be removed to expose the drilled passages.

Throttle and Choke

Examine the throttle and choke shaft, and carburetor body at the bearing points and holes into which the linkage is fastened, and replace if worn or damaged. Any excessive wear in these areas can cause dirt to enter the engine and cause premature wear. If dust seals are present, check the seal condition and the correct placement next to the carburetor body.

Idle and High Speed Mixture Adjusting Screw

Examine the idle mixture needle tip and tapered surface for damage. The tip and tapered surface of the needle must not show any wear or damage. If either is worn or damaged, replace the adjusting needle. Tension is maintained on the screw with a coil spring. Replace the “O” ring seal if removed (diag. 34).

Examine the tapered surface of the high speed mixture needle. If the tapered surface is damaged or shows wear, replace the needle.

"O" RING

RETAINER NUT

BRASS WASHER

SPRING

HIGH SPEED

ADJUSTMENT

SCREW

34

Fuel Bowl Retaining Nut

The bowl nut contains the passage through which fuel is delivered to the high speed and idle fuel system of the carburetor. If a problem occurs with the idle system of the carburetor, examine the small fuel passage in the annular groove in the bowl nut. This passage must be clean for the proper transfer of fuel into the idle metering system.

Bowl nuts that are used on adjustable main, float style carburetors may use either one or two metering ports. This difference relates to calibration changes of the carburetor, depending on the application (diag. 35).

NOTE: DO NOT INTERCHANGE BOWL NUTS.

The fuel inlet ports must be free of any debris to allow proper fuel flow.

 

IDLE FUEL

FUEL-

FUEL-

TRANSFER

INLET

METERING

PASSAGE

 

PORT

 

ONE-HOLE TYPE TW0-HOLE TYPE

35

 

16

Fuel Bowl, Float, Needle and Seat

NOTE: To prevent damage to the float bowl on Series 7 carburetor, pull straight up with a needle nose pliers in the pocket closest to the main fuel well (diag. 37).

The float bowl must be free of dirt and corrosion. Clean the bowl with solvent or carburetor cleaner (soak 30 minutes or less).

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. Replace any damaged or worn parts.

The needle and seat should be replaced if any fuel delivery problems are experienced (flooding or starvation). Sealing problems with the inlet needle seat may not be visible and replacement is recommended. Only the inlet needle is serviceable on the Walbro model LMK carburetor.

FLOAT HINGE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SEAT

 

PIN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NEEDLE

 

 

 

 

FLOAT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NEEDLE &

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPRING CLIP

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SEAT

MAIN NOZZLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HINGE PIN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SEAT

EMULSION

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RETAINING

"O" RING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"O" RING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RING

POSITIONED IN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GROOVE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOZZLE

 

 

 

 

SPRING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IDLE RESTRICTION

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BOWL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"O" RING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

POSITIONED IN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

'O' RING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GROOVE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MAIN JET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BOWL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MAIN JET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPRING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GASKET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WASHER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

JET/BOWL NUT

 

BOWL RETAINER

BOWL DRAIN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

38

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

36

 

 

 

37

 

 

 

 

 

SERIES 8, 9 & 10

 

SERIES 7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHOKE SHAFT

 

 

 

 

 

 

 

 

 

 

THROTTLE SHAFT & LEVER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THROTTLE SHAFT

 

 

 

 

 

 

THROTTLE RETURN SPRING

 

 

 

 

 

 

 

 

THROTTLE SHUTTER

 

 

 

 

THROTTLE DUST SEAL

 

 

 

 

DUST SEAL WASHER

 

CHOKE DUST

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DUST SEAL

 

SEAL

THROTTLE RETURN SPRING

 

THROTTLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FUEL FITTING

 

 

 

 

IDLE SPEED SCREW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHOKE RETURN

 

SHUTTER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPRING

WELCH PLUG

 

SCREW

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PRIMER BULB/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHOKE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IDLE MIXTURE

 

RETAINER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SHUTTER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SCREW

 

 

RING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TENSION SPRING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THROTTLE SHUTTER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"O" RING

 

FUEL FITTING

 

 

 

 

 

PRIMER BULB

 

 

 

 

 

 

 

&nbsnbsp;

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SCREW

 

 

FILTER

 

 

 

 

 

 

 

SEAT AND CLIP INLET

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

INLET NEEDLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ATMOSPHERIC VENT

 

 

 

 

 

 

 

NEEDLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SPRING CLIP

 

FLOAT

 

 

FLOAT SHAFT

 

 

WELCH PLUG

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FLOAT SHAFT

 

 

 

 

 

 

 

 

FLOAT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

"O" RING

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FLOAT BOWL

 

 

 

 

FLOAT BOWL

 

 

 

 

 

 

 

 

 

 

 

BOWL NUT WASHER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BOWL NUT WASHER

 

 

 

 

 

 

 

 

 

 

 

HIGH SPEED BOWL NUT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BOWL NUT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WALBRO LMK

39

 

 

 

 

SERIES 6

40

17

ASSEMBLY PROCEDURE

Welch Plugs

To install a new welch plug after cleaning the carburetor, secure the carburetor in a vise equipped with protective jaws. Place the welch plug into the receptacle with the raised portion up. With a punch equal to the size of the plug hole, merely 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 (diag. 41).

NEW WELCH PLUG

 

FLAT END PUNCH

 

 

 

SAME OR

 

 

 

 

LARGER

 

 

 

 

DIAMETER OF

 

 

 

 

 

 

 

 

PLUG HOLE

 

 

41

 

 

 

 

 

Throttle Shaft and Plate

 

 

 

When reassembling Tecumseh or Walbro carburetors,

THROTTLE

 

THROTTLE

PLATE

 

LEVER

it is important that the lines, lettering, or numbers on

 

 

TWELVE

the throttle plate are facing out when in the closed

 

 

O'CLOCK

position. If the throttle plate has only one line, this

 

 

POSITION

line should be positioned in the 3 o’clock position on

 

 

 

Series 3, 4, and 7 carburetors, and at the 12 o'clock

 

 

 

position on Series 1, 6, 8, 9 carburetors. (diag. 42 &

 

 

 

43).

 

42

Test the operation of the throttle and return spring if

 

 

 

 

equipped. If binding occurs, correct by loosening the

 

 

THREE

screws and repositioning throttle plate.

 

 

 

 

 

O'CLOCK

Always use a new screw(s) when reinstalling the

 

 

POSITION

throttle shutter to prevent the screws from loosening

 

 

 

and being drawn into the engine. New Tecumseh

 

 

 

screws are treated with dry-type adhesive to secure

 

 

 

them in place.

 

 

 

NOTE: NEVER REUSE OLD SCREWS.

 

43

 

 

On Walbro LMK and Series 7 carburetors, install the

 

DUST SEALS

throttle return spring on the throttle shaft with the

 

 

 

squared end up. Slide the foam dust seal over the

 

 

spring. Insert the throttle lever assembly into the

 

 

carburetor body with both tangs of the return spring

 

 

on the left side of the center boss (viewed from throttle

 

 

end) and the flat side of the shaft toward the carburetor

 

 

mounting flange. Install the throttle shutter to the

 

 

throttle shaft using notes or marks to place the shutter

 

 

as originally found (Series 7 must have the line on the

 

 

shutter at the 3 o'clock position) (diag. 44).

 

 

Always use new throttle shutter screws when

 

44

reinstalling. Install the screws so they are slightly

SERIES 7

 

loose. Apply light downward pressure on the throttle

 

 

shaft and rotate it clockwise to seat the throttle shutter

THROTTLE LEVER

 

in the bore, then tighten the throttle shutter screws.

 

 

 

Check for binding by rotating the throttle shaft. If

THROTTLE PLATE

 

necessary, adjust the throttle shutter by loosening and

 

 

 

repositioning the shutter, then retighten the screws

 

 

(diag. 45).

 

 

WALBRO LMK SERIES

45

18

Choke Shaft and Plate

 

 

The choke plate is inserted into the air horn of the

CHOKE PLATE

carburetor in such a position that the flat surface (if

 

applicable) of the choke is down. Choke plates will

 

operate in either direction. Make sure it is assembled

 

properly for the engine. Test the operation of the choke

 

and return spring function if equipped (diag. 46).

 

Always use a new screw(s) when reinstalling the

 

 

 

choke shutter as the screws are treated with dry-type

 

 

 

adhesive to secure them in place.

 

FLAT DOWN

46

NOTE: NEVER REUSE OLD SCREWS.

 

 

 

 

The choke shaft and plate must be in the closed

 

 

SPRING

 

 

HOOKUPS

position prior to tightening the screws. Hard starting

 

 

 

 

 

may be due to insufficient choking action because of

 

 

 

a misaligned choke plate. Correct by readjusting the

 

 

 

choke plate to close completely. Note the cutout

 

 

 

position of choke shutter if applicable.

 

 

 

On Walbro LMK and Series 7 carburetors, install the

 

 

 

choke return spring on the choke shaft with the

 

 

 

squared end up and hooked into the notch in the plate.

 

 

 

Work the dust shield up around the spring and insert

 

 

47

the choke shaft into the carburetor body. Rotate the

 

 

 

 

 

shaft counterclockwise until the tang on the spring

PRESS IN PARTIALLY

SOME INLET FITTINGS

rests against the left side of the center boss on the

THEN APPLY

 

 

carburetor body (viewed from choke end) . Rotate the

 

 

LOCTITE

STRAINER

 

choke shaft approximately 1/4 turn counterclockwise

 

 

 

and insert the choke shutter into the slot in the choke

 

 

 

shaft. Make sure the tabs on the shutter lock the choke

 

 

 

shaft between them. Rotate the shaft and check for

 

 

 

binding, the choke must return to the open position

 

 

 

when released (diag. 47).

 

 

 

Fuel Inlet Fitting

 

 

48

 

 

 

When installing the fitting, insert the tip into the

 

 

 

 

 

 

 

 

 

 

 

 

 

carburetor body. Support the carburetor body with a

 

 

 

 

 

 

 

 

 

 

 

 

 

wood block to avoid damage to other parts. Use a

 

 

RETAINER NUT

 

 

 

 

 

"O" RING

 

 

 

 

 

 

 

 

 

bench vise or press to install the fitting squarely. Press

 

 

 

 

 

 

 

 

 

 

BRASS WASHER

 

it in until it bottoms out (diag. 48).

 

 

 

 

 

 

 

 

 

 

 

SPRING

 

High and Low Speed Adjusting Screw, Main

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Nozzle

 

 

 

 

 

 

 

 

 

 

 

HIGH SPEED

 

When reassembling, position the coil spring on the

 

 

 

 

 

 

 

 

 

 

 

ADJUSTMENT

49

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SCREW

adjusting screws, followed by the small brass washer

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

and the “O” ring seal. Turn the high speed adjustment

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

screw into the bowl nut and the low speed mixture

FLOAT HINGE PIN

 

 

 

 

 

 

 

 

 

 

screw into the carburetor body (diag. 49).

 

 

 

 

 

 

 

 

 

 

 

 

 

Some carburetors may have a fixed main mixture or

NEEDLE &

 

 

 

FLOAT

 

both a fixed idle mixture and main mixture, and are

 

 

 

 

 

 

 

 

 

 

SEAT

 

 

 

 

 

 

 

 

 

 

not adjustable.

 

 

 

 

 

 

 

 

 

 

 

 

 

On Series 7carburetors, place the main nozzle spring

SEAT RETAINING

 

MAIN NOZZLE EMULSION

 

 

 

 

 

 

 

 

 

 

 

into the main nozzle cavity. Apply oil to the main nozzle

RING

 

 

 

"O" RING POSITIONED IN

"O" ring and push the main nozzle into the cavity

 

 

 

 

 

 

GROOVE

 

with the "O" ring end in first.

 

 

 

 

SPRING

 

Next install the "O" ring in the main jet cavity. Place

 

 

 

 

 

 

IDLE RESTRICTION

 

the spring over the shoulder on the main jet and push

 

 

 

 

 

 

 

 

 

 

 

BOWL

 

the jet into the cavity with the main jet toward the "O"

 

 

 

 

 

 

 

 

 

 

 

 

ring. Place a new gasket on the drain screw and

 

 

 

 

 

 

 

"O" RING

 

tighten in position (diag. 50).

 

 

 

 

 

 

 

 

 

MAIN JET

 

On Walbro LMK carburetors, the main jet can be

 

 

 

 

 

 

 

 

 

 

 

MAIN JET SPRING

 

 

 

 

 

 

 

 

 

 

 

GASKET

 

replaced by pressing it into the center leg of the

 

 

 

 

 

 

 

 

 

 

 

BOWL

 

carburetor until flush. (diag. 31 page 15).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

DRAIN

 

 

 

 

 

 

 

 

 

 

 

 

NOTE: FOR HIGH ALTITUDE JETTING, CONSULT

 

 

 

 

 

 

BOWL RETAINER

50

BULLETIN 110.

 

 

 

 

 

 

 

 

 

 

 

 

 

19

Inlet Needle and Seat

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) flat punch, making sure it is firmly seated (diag. 51). On Series "7" carburetors, install the seat retainer into the cavity and push it down using the flat punch until it contacts the seat.

PUSH IN UNTIL SEAT RESTS ON BODY SHOULDER

IF YOUR CARBURETOR HAS A STEEL SEAT RETAINING RING RE-INTSALL AFTER SEAT INSTALLATION

INLET NEEDLE

SEATS AT THIS

POINT

5/32" (3.969 mm)

FLAT PUNCH

SEAT

INSERT THIS

FACE FIRST

51

The inlet needle hooks onto the float tab by means of a spring clip. To prevent binding, the long, straight end of the clip should face the choke or air filter end of the carburetor as shown (diag. 52).

LONG END

 

 

 

 

CLIP

 

 

 

 

 

 

 

 

OPEN END OF CLIP

OF CLIP

 

 

 

Points toward choke

 

 

end

 

THROTTLE

 

 

 

 

 

 

 

 

 

 

END

CHOKE

 

 

END

52

 

 

 

 

Float Installation

On Series 7 carburetors, slide the hinge pin into the hinge on the float. Position the needle into the fuel inlet and snap the float pin into the tabs on the float bowl. Float height is not adjustable.

On Series 7 carburetors and the Walbro LMK, reinstall the inlet needle on to the float and place it into the carburetor (diag. 53).

1.When rebuilding a carburetor with a clip on the needle, position carburetor float side up for assembly.

2.Place the inlet needle and spring clip onto the float as shown. The long end of the spring clip must point towards the choke end of the carburetor. This will ensure that the inlet needle will move up and down in a straight line (diag. 53).

3.To set the proper float height on carburetors except Series 7 and Walbro LMK, see adjusting procedure.

4.Some Tecumseh float style carburetors have a damper spring which is installed as shown in diag. 55.

SERIES 7 WALBRO / LMK

53

 

 

 

CLIP

 

OPEN END

 

OF CLIP

LONG END

 

OF CLIP

 

Points toward choke end

54

 

 

 

 

POINTS TOWARD

 

THE CHOKE END

 

55

20

Fuel Bowl And Bowl Nut

Whenever a carburetor bowl is removed for service, the fuel bowl “O” ring (or gasket on Series "7") and the bowl nut washer must be replaced. For easier installation, lubricate the “O” ring with a small amount oil.

Installing the Float Bowl

Install the float bowl by placing the detent portion opposite of the hinge pin. Make sure the deepest end of the bowl is opposite of the inlet needle. The bowl has a small dimple located in the deepest part. The purpose of this dimple is to minimize the chances of the float sticking to the bottom of the bowl caused by stale fuel.

Impulse Fuel Pump

The diaphragms must be installed against the center body with the gaskets against the outside covers. The parts are designed so they cannot be misassembled without damage (diag. 57).

To test the unit, assemble the carburetor to the engine, leaving the fuel line from the pump off. Use a different fuel tank remotely placed above the carburetor to provide gravity fuel flow to the carburetor inlet to run the engine while testing the pump. Make sure fuel is available in both fuel tanks and the original fuel tank's fuel line is connected to the fuel pump inlet. Place the pump outlet line in a proper draining receptacle. With the pulse line connected from the engine crankcase to the pump and the engine running, a definite fuel flow should result at the pump outlet.

If the flow is erratic or intermittent, the pump needs repair or replacement.

Primer Bulb

To install, start the retainer and bulb into the casting with the retainer tabs pointed out. Firmly push the bulb and retainer into position using a 3/4'’ (19.05 mm) deep well socket (diag. 58).

Final Checks

Before reinstalling a newly overhauled carburetor, pre- set the main mixture adjustment screw, the idle mixture adjustment screw and the idle speed adjustment screw. See “Pre-sets and Adjustments” in this chapter.

DETENT

56

CARBURETOR

FITTING

VALVE CLOSED

VALVE OPEN

 

ATMOSPHERIC

 

DIAPHRAGM

 

VENT

 

 

 

 

FILTER

 

 

AIR BLEED

VALVE OPEN

VALVE CLOSED

 

FUEL SUPPLY

PULSE LINE

 

 

TO CRANKCASE

êCRANKCASE PRESSURE

êCRANKCASE SUCTION AND

á SUCTION FUEL FLOW DIRECTION

áATMOSPHERIC PRESSURE ACTING

FLOW DIRECTION

ATMOSPHERIC PRESSURE

ON DAMPING DIAPHRAGM

ATMOSPHERIC PRESSURE

êCAUSED FUEL FLOW

áFUEL FLOW

á ACTING ON DAMPING

 

 

DIAPHRAGM

 

 

 

57

58

21