FUEL SYSTEM/CARBURETION
4.18
TROUBLESHOOTING
FUEL STARVATION/LEAN
MIXTURE
Symptoms: Hard start or no start, bog, backfire, popping through intake / exhaust, hesitation, detonation, low
power, spark plug erosion, engine runs hot, surging, high idle, idle speed erratic.
S
No fuel in tank
S
Restricted tank vent, or routed improperly
S
Fuel lines or fuel valve restricted
S
Fuel filter plugged
S
Carburetor vent line(s) restricted
S Plugged or restricted inlet needle and seat screen or inlet passage
S Clogged jets or passages
S Float stuck, holding inlet needle closed or inlet needle stuck
S Float level too low
S Fuel pump inoperative
S Air leak at impulse line
S Restricted impulse line (kinked, pinched)
S Intake air leak (throttle shaft, intake ducts, airbox or air cleaner cover)
S Ruptured vacuum slide diaphragm or poor seal between diaphragm and slide, vacuum slide
stuck closed or sticky
S Improper spring
S Jet needle position incorrect
S Incorrect pilot screw adjustment
RICH MIXTURE
Symptoms: Fouls spark plugs, black, sooty exhaust smoke, rough idle, poor fuel economy, engine runs rough/
misses, poor performance, bog, engine loads up, backfire.
S Air intake restricted (inspect intake duct)
S Air filter dirty/plugged / oil saturated or water saturated
S Choke plunger sticking, incorrectly adjusted choke
S Choke cable binding or improperly routed
S Incorrect fuel screw adjustment
S Faulty inlet needle and seat
S Faulty inlet needle seat O-Ring
S Float level too high
S Poor fuel quality (old fuel)
S Loose jets
S Worn jet needle/needle jet or other carburetor parts
S Dirty carburetor (air bleed passages or jets)
S Weak or damaged vacuum piston return spring
S Fouled spark plug
S Restricted breather system
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