TOPIC 6. CARBURETOR

TM 10-3930-644-14&P

TOPIC 6. CARBURETOR

A. DESCRIPTION

The carburetor used in this fuel system is a single

venturi, updraft type with fixed jets covering all speeds

except idle.

It has an airbleed well method of

compensation, an idle fuel adjusting screw and an idle

throttle stop screw. The air intake of the carburetor is

provided with a choke valve control. The flow of fuel

through the main jet system is controlled by the size of

the jet The idle adjusting screw controls the fuel mixture

for the idle system.

B. CHOKE VALVE ADJUSTMENT

To aid in starting a cold engine, a choke valve is

provided in the air inlet of the carburetor. By closing this

valve, a rich mixture of fuel is drawn into the carburetor

for quick starting.

It is only necessary to make certain the choke control

fully opens the valve by the time the engine has reached

normal operating temperature and choke control button

Figure 6-1. Carburetor

is pushed all the way in. Adjustment is made at the

swivel connection on the choke shaft lever.

NOTE

Before

making

any

carburetor

C. CARBURETOR ADJUSTMENTS

adjustments, allow the engine to

warm up to normal operating

NOTE

temperature.

Before any work is performed on

carburetor, make sure the trouble is

Make carburetor adjustments as follows:

not due to poor compression, or in

the ignition system due to incorrect

1. Throttle stop-screw adjustment:

The throttle

timing, fouled spark plugs, burned

Idling stop-screw should be turned in against the

ignition points, etc.

stop to hold the throttle open slightly. Then,

after the idle fuel adjustment is made, adjust the

Refer to REPAIR MANUAL for CARBURETOR REPAIR.

stop-screw to obtain an idle speed of between

500 and 550 r.p.m.

The correct mixture of fuel and air is controlled by a fixed

main jet and an adjustable idle fuel jet. The idle throttle

2. Idle fuel adjustment: Turn idle adjustment screw

stop screw controls the throttle position to ensure correct

in to obtain a lean mixture or turn out to obtain a

engine idle speed.

rich mixture. During adjustment, engine speed

may increase or decrease. Adjust idle screw

Adjustments are properly set when the unit is shipped

until the engine runs smoothly and steadily. It

from the factory and if they have to be disturbed the

may be necessary to reset throttle stop-screw to

carburetor must be readjusted.

obtain correct idle speed.

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