"F" SERIES ENGINE FUEL SYSTEM FUEL SYSTEM COMPONENTS AND THEIR FUNCTION

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FUEL TANK Stores

FUEL FILTER Filt e r s out dirt and water, allowing only clean fuel to enter fuel line.

VENTED FUELCAP PNEUMATIC PRIMER ASSEMBLY Forces compressed air into the float chamber which forces into carburetor venturi. AIR VANE GOVERNOR and closes throttle, controlling engine r.p.m.

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AIR FILTER Keeps dirt from entering carburetor with air.

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VALVES Permitfuelmixtureto THROTTLE DISC FLOAT BOWL Resentercrankcase on compressionstrokeVariesthe volume of ervoir of fuelfor meand trapfuelmixtureincrankcase on fueland air mixturetotering to carburetor power

stroke.

The carburetor starts its action and operates as follows:

1. The crankshaftrotates when the starter rope is pulled (or electric starter motor engaged electric start models).

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2. The rotating crankshaft moves the piston up and down in the cylinder. This creates pressure andvacuum alternatelyinthe crankcase. PRESSURE I N CRANKCASE

3. The vacuum created by movement of the pistonupwardin the cylinderopens a reed valve then air rushes through the throat of the carburetor.

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VACUUM IN CRANKCASE

4. The carburetor throat is a Venturi tube, large at each end with a smaller center passage, When air rushesthroughthis tube, the air pressure at thecenter is

PRESSURE AREA

less. 5. By inserting a tube from the carburetor float bowl into this center area, the difference in air pressure will forcefuel up through this tube, where it is picked up by, and mixed with, the air. 4-29

"F" SER ES (Cont.) ENGINE F UEL SYSTEM FUEL SYSTEM COMPON NTS AND THEIR FUNCTION 6. Turbulence around the throttle to mix the fuel and air.

disc helps

7. A s fuel and air mixture enters the crank-

case through the reed valves, it is near a gaseousstate. Theengine, when cold, will not vaporize the mixture completely. A s the engine warms up, themixture is heatedinthecrankcaseandbecomes a consistently even gas.

PRIMER OPERATION

Examine the primersystem. A pneumaticprimer forces compressed air into the float bowl chamber which forces fuel into the carburetor venturi for cold enginestarting. PRIMER ACTIVATED

1/2 TURNSETTING

Float

The float valve consistsof a needle and seat assembly activated by a cork float in the float bowl. The needle rests on the float arm and is held in place by a spring clip. The needle is rubber-tipped it will readily seal against the brass seat.

so

If the float bowl is empty, the cork float rests on the bottom of the bowl. As fuel enters the float bowl, the float rises, moving the needle into the seat, shutting off the fuel supply. As the engine uses fuel, the float drops slightly and the needle movesoff the seat, maintaining a constant fuel supply to the engine. PRIMER HOSE

The carburetor is completely automatic. A s fuel enters a singlemeteredjet it is mixed with incoming air to from the correct combustiblemixture.Theamount of fuel flow throughthemetering jet is regulated by the altitude needle. There are no adjustmentsto be madeto regulatethe amount of fuelentering the carburetor venturi. There is an atmospheric pressure adjustment that would have to be made if ' t h e engine is operatingin very high o r very low altitudes. All carburetorsrequire a finaladjustment of thealtitudeneedlepriortoputtingthe mower into service.

To adjust, proceed a s follows: 1. Pre-set altitudeneedle seat. CLIP 4-30

2. Start engineandallow minutes to warm up.

1/2 turnfrom

to run for 3 to 5

“F” SERIES (Cont.) ENGINE FUEL SYSTEM FUEL SYSTEM COMPONENTS AND THEIR FUNCTION AIR ADJUSTMENT (CONTINUED)

3. Placespeedcontrollever in HIGH SPEED running position (3100-3300R.P.M.)Observe engine operation.If not running smoothly,turn altitude needle counterclockwise approximately at a time to Obtain proper engine operation.

4. Slowly turn altitude needlecounterclockwise until engine is running smoothly. Allow engine to run for one or two minutes to make sure adjustment is not toolean.

The governor will control the amount of air/fuel entering the engine. The purpose of the atmospheric pressure adjustingneedle is to mix the right amount of fuel with the correct amount of incoming air. 7. In the position no is the carburetor vent passage. Therefore, the float bowl pressure has been eliminated and the fuel supply to the carburetor venturi is cut off, stopping the engine. CLOSED SETTING

LOW SPEED running position (2400-2600R.P.M.) and check operation.

5. Place speedcontrolleverin

carburetor adjustment is completed,shut off engine. IMMEDIATELY attempt restart to engine. DO NOT PRIME A HOT ENGINE. It should start within 2 pulls on starter handle. Check startingengineat both HIGH and LOW speed settings. If difficult to restart, turnaltitudeneedle 1/8 turncounterclockwise to richen fuel mixture and obtain easy restarting.

6. After

FUEL TANK VENTING Fuel tanks must be vented to prevent vacuum forming and stopping flow of fuel. Tank caps will have a vent hole. A closed vent will create a vacuum in the tank as fuel is used and eventuallycausethe engine to stop. In a few minutes the vacuum will decrease and the engine can be started again, but it will stopagainin a short period of time, The ventholecanbecome clogged with dirt, Check venthole beforeeach operation and clean if necessary.

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BAFFLE

"F" SERIES (Cont.)' ENGINE FUEL SYSTEM FUEL SYSTEM COMPONENTS AND THEIR FUNCTION FUEL TANK VENTING (Cont.) PRIMER HOSE AIR VANE

LINE

GASKET

I

SHUT-OFF VALVE The fuel tank screen assembly or the shutoff valvecanbecome clogged. Thiscan be checked easily by removingthefuelhose, opening thevalve and observing for fuel flow throughthe valve. Replacethefuel shut-off assembly if damaged. Shut-off valve is secured to fuel tank with a spring clip; exercise care when re-installing to fuel tank.

ADJUSTMENT NEEDLE

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FLOAT

The carburetor used on the early model F series engines is automatic. No fuel adjustments are necessary to regulate fuel intake.A single, meteredjet allows the correct amount of fuel to mix with the incoming air which is regulated by a single adjusting needle. Adjustment must be changed when a significant changein altitude is encountered.

SAFETY WARNING DO NOT SUBSTITUTE WITH INFERIOR FUEL HOSE WHICH MAY CAUSE LEAKAGE FROM PREMATUNEDETERIORATION.LEAKAGE OF FUEL MAY CAUSE AN EXPLOSION AND/OR FIRE.

Two plastic plugsare available and recommended for installation inthe screw holes located in the back wall of the air filter box. Dirt then is prevented from entering the air box. The part number is 611545. 4-32

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. .... ..... SERVICEBULLETINREFERENCES

REVISED 1983

"F" SERIES (Cont.) AIR FlLTER If engine is flooded, fuel can drain back into filter, As filter becomes saturated, incoming air picks up morefuel,causing greater flooding. A puckered filter will allow air and dirt tobypassfilter. Make certain that filter covers cup area. If oiled properly, filter is very efficient. First wash out with fuel, o r solvent, blow dry with compressed air, then apply 10 to 15 drops of oil, Squeeze severaltimestodistribute oil. If engine "smokes"for no apparent reason, filter may be saturated with fuel mix o r may need cleaning.

On later production models the air filter cover was retained with a clipor bail.

A dirty air cleaner element create anoticeablepower may reduce engine life.

will loss, and

Operating engine without filterelement, or filter element without sufficientoil will shorten engine life. Reinstall filter in the same position which it was removedtoprevent imbedded particlesinintakeside from entering carburetor.

To remove grasp the cover, loosen snap and open cover. NOTE

On early models the air filter element MUST BE installed so the smalladditional piece faces the venturi opening as illustrated. Also make sure it is positioned Squarely between both screw holes. If incorrectlyinstalled, the corner of the secondary filter will be drawn into carburetor throat thereby restricting air flow, resulting in a rich fuel mixture entering the engine. Later production, this small square piece (filter)was eliminated.