20-2
TROUBLESHOOTING
ENGINE LACKS POWER
Possible cause
• Clogged air cleaner
• Restricted fuel flow
• Clogged fuel tank cap breather hole
• Clogged muffler
Engine speed increase
Correct
Normal
Not fouled or discolored
Not overheating
4. Check carburetor for clogging
5. Remove and inspect spark plug Fouled or discolored
6. Check if engine overheats Overheating
7. Try rapid acceleration or run
at high speed
Engine knocks
Engine speed does not
increase sufficiently
1. Raise rear wheel off ground and
accelerate lightly
Normal compression
Clogged
• Faulty ignition control module (ICM)
• Faulty ignition pulse generator
• Carburetor not serviced frequently enough
• Plug not serviced frequently enough
• Use of plug with improper heat range
• Lean fuel mixture (section 5)
• Wrong type of fuel
• Excessive carbon build-up in combustion
chamber
• Ignition timing too advance (Faulty ICM or
ignition pulse generator)
• Drive and driven pulleys/clutch slipping
(section 10)
• Any extra modification
• Excessive carbon build-up in combustion
chamber
• Wrong type of fuel
• Lean fuel mixture (section 5)
• Ignition timing too advance (Faulty ICM or
ignition pulse generator)
• Throttle position switch faulty
Incorrect2. Check ignition timing
3. Test cylinder compression Low compression • Valve clearance too small
• Improper valve and seat contact
• Worn cylinder, piston and piston rings
• Valve stuck open
• Improper valve timing
• Leaking cylinder head gasket
• Loose spark plug
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