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.
• No fuel in tank
• Restricted tank vent, or routed improperly
• Fuel lines or fuel valve restricted
• Fuel filter plugged
• Carburetor vent line(s) restricted
• Plugged or restricted inlet needle and seat screen or inlet
passage
• Clogged jets or passages
• Float stuck, holding inlet needle closed or inlet needle stuck
• Float level too low
• Intake air leak (throttle shaft, intake ducts, airbox or air
cleaner cover)
• Jet needle position incorrect
• 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.
• Air intake restricted (inspect intake duct)
• Air filter dirty / plugged
• Choke plate sticking, incorrectly adjusted choke
• Choke cable binding or improperly routed
• Incorrect pilot air / fuel screw adjustment
• Faulty inlet needle and seat
• Faulty inlet needle seat O-Ring
• Float level too high
• Poor fuel quality (old fuel)
• Loose jets
• Worn jet needle / needle jet or other carburetor parts
• Dirty carburetor (air bleed passages or jets)
• Weak or damaged choke plate return spring
• Fouled spark plug
Poor Idle
Idle Too High
• Idle adjusted improperly / air mixture screw damaged
• Throttle cable sticking, improperly adjusted, routed
incorrectly
• Choke cable sticking, improperly adjusted, routed incorrectly
• Plugged or restricted pilot jet
Idle Too Low
• Choke cable bending or incorrectly adjusted
• Idle speed set incorrectly
• Air mixture screw misadjusted or damaged
• Belt dragging
• Ignition timing incorrect
• Worn jet needle / needle jet
• Plugged or restricted pilot jet
Erratic Idle
• Choke cable bending or incorrectly adjusted
• Throttle cable incorrectly adjusted
• Air leaks, dirty carburetor passages (pilot circuit)
• Pilot mixture screw damaged or adjusted incorrectly
• Tight valves
• Ignition timing incorrect
• Belt dragging
• Dirty air cleaner
• Engine worn
• Spark plug fouled
• Idle speed set incorrectly
• Worn jet needle / needle jet
• Plugged or restricted pilot jet
5.19
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