4.14
FUEL SYSTEM / CARBURETION
• Ruptured vacuum slide diaphragm, vacuum slide stuck
closed or sticky
• Improper spring
• 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 plunger 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 vacuum piston return spring
• Fouled spark plug
Poor Idle / Idle Too High
• Idle adjusted improperly / idle mixture screw damaged
• Sticky vacuum slide
• Throttle cable sticking, improperly adjusted, routed
incorrectly
• Choke cable sticking, improperly adjusted, routed
incorrectly
• Plugged or restricted idle jet
Idle Too Low
• Choke cable bending or incorrectly adjusted
• Idle speed set incorrectly
• Idle mixture screw adjusted incorrectly or damaged
• Belt dragging
• Ignition timing incorrect
• Worn jet needle/needle jet
• Plugged or restricted idle 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 (speed limiter)
• Worn jet needle/needle jet
• Plugged or restricted idle jet
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