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Complaint
Engine runs poorly in
low speed range
Engine runs poorly in
high speed range
Engine speed does not
return smoothly
Exhaust valve does not
work
Spark plug does not
ignite
Carbon deposits on
spark plug porcelain
Spark plug electrode
damage
Possible Cause
Exhaust valve maladjustment
Wide spark plug gap
Carburetor air screw maladjustment
Incorrect carburetor fuel level
Improper jet needle size
Incorrect ignition timing
CDI unit malfunction
Throttle position sensor malfunction
Ignition coil damage
Magneto malfunction
Magneto short circuit
Exhaust valve breather hose clogged
Narrow spark plug gap
Incorrect carburetor fuel level
Incorrect main jet setting
Power jet solenoid malfunction
Retarded ignition timing
CDI unit malfunction
Ignition coil damage
Air cleaner element clogged
Magneto short circuit
Exhaust pipe cracked
Exhaust valve malfunction
Piston ring stuck
Too high engine idle speed
Carbon deposits on exhaust valve
Exhaust valve damage
Governer damage
Exhaust valve shaft damage
Valve spring damage
Exhaust valve breather hose clogged
Ignition coil malfunction
Spark plug malfunction
Magneto malfunction
CDI unit malfunction
Wide spark plug gap
Engine kill switch malfunction
Too rich air/fuel mixture
Too rich oil/gasoline mixture
Improper spark plug heat range
Improper spark plug heat range
Overheating
Incorrect ignition timing
Loose spark plug
Too lean air/fuel mixture
TROUBLESHOOTING
18-3
Remedy
Adjust
Adjust or replace
Adjust
Adjust
Replace
Adjust
Replace
Replace
Replace
Replace
Replace
Clean
Adjust or replace
Adjust
Adjust
Replace
Adjust
Replace
Replace
Clean or replace
Replace
Replace
Clean, adjust or
replace
Replace
Adjust
Clean
Replace
Replace
Replace
Replace
Clean
Replace
Replace
Replace
Replace
Adjust
Repair or replace
Adjust
Adjust
Replace
Replace
!2-4
Adjust
Tighten
Adjust
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