7
FUEL SYSTEM
(all models)
CARBURETOR
Carburetors are adjusted in the factory and under normal conditions require no further adjustment. If, however,
one of the following conditions exist, readjustment of the carburetor may be needed.
CONDITION
POSSIBLE CAUSE/PROBABLE REMEDY
A.
Black, sooty exhaust smoke, engine sluggish.
A.
Mixture too rich - readjust main fuel needle.
B.
Engine misses and backfires at high speed.
B.
Mixture too lean - readjust main fuel needle.
C.
Engine starts, sputters and dies under cold
weather starting.
C.
Mixture too lean - turn main fuel adjustment 1/4
turn counterclockwise.
D.
Engine runs rough or stalls at idle speed.
D.
Improper idle adjustment - readjust idle fuel
needle.
Maximum power and efficiency are possible only with proper carburetion. Improper carburetor adjustment can
lead to overheating, fouled spark plug, excessive value wear and other problems. Do not neglect carburetor if any
of the above problems persist. The following adjustment procedure is for the standard side draft carburetors.
STEP 1 - Stop engine and carefully turn Main Fuel and Idle Fuel Needle adjusting screws all the way in
(clockwise direction) until they bottom - DO NOT FORCE SCREWS as this will damage needle valves.
STEP 2 - For preliminary adjustment, turn Main Fuel screw 2 turns in counterclockwise direction, turn Idle Fuel
screw 1 - 1/4 turns in counterclockwise direction.
STEP 3 - Start engine and operate at normal speed until normal operating temperatures are reached.
STEP 4 - Main Fuel Adjustment - With engine operating at full throttle and full load, turn Main Fuel Needle in
(clockwise) until engine slows down (lean), note position of screw, then turn needle out
(counterclockwise) until engine regains speed and then again slows down (overrich). Turn needle back
in until it is positioned halfway between lean and overrich settings. If adjusted properly, the engine
should accelerate smoothly and operate with steady governor action.
STEP 5 - Idle Fuel Adjustment - Operate engine at idle speed of about 1000 RPM (adjust Idle Speed screw until
this speed is attained - check with tachometer). Turn Idle Fuel Needle in (clockwise) until engine slows
down and idles rough then turn screw out until engine speeds up and idles smoothly at the desired idle
speed.
STEP 6 - Final Adjustment - Since main fuel and idle fuel adjustment have some affect on each other, recheck
engine and make final adjustments as necessary to achieve smoothest operation.
NOTE: If the preceding steps do not remedy problems attributed to carburetor, carburetor reconditioning may be
necessary.
Carburetor Reconditioning
Service difficulties with fuel systems usually originate from improper carburetor adjustments or dirt, gum or
varnish in components. It will be necessary to completely disassemble carburetor to clean thoroughly. Normally
only pre-season cleaning will be required; however, the frequency of cleaning will depend upon use and operating
conditions.
All parts should be cleaned in a solvent. Gum is easily removed with an alcohol or acetone solvent. Be sure
any carbon deposits are removed from bore, especially where throttle plate seats in casting. Blow out all passages
with compressed air. Replace all worn and damaged parts. Always use new gaskets. Carburetor repair kits are
available for most carburetors. They include the bowl nut gasket, bowl ring gasket, float pin, bowl baffle gasket
and fuel inlet needle and seat.
