Poor High Speed Performance - Yamaha YTZ250S 1986 Service Manual

Poor high speed performance
Ignition System
Possible Cause Remedy
1.
Spark plug is dirty or plug gap is
• Clean or replace
too narrow.
2.
C.D.I. unit is faulty.
• Replace
3.
C.D.I. magneto is faulty.
• Replace
4.
Ignition coil is faulty.
• Replace
5. Ignition timing is incorrect.
• Adjust
6. Loose wire connection.
•
Repair
Compression System
Possible Cause Remedy
1. Piston rings are sticking or worn.
• Replace
2.
Cylinder or piston is worn or
• Repair or replace
scratched.
3.
Compression leakage through
• Repair or replace
crankcase sealing surfaces or
crankshaft side oil seal.
4. Carbon deposits in combustion
• Decarbonize
chamber (Piston, Cylinder head).
5. Power valve malfunctions.
• Repair or replace
Air / Fuel System
Possible Cause Remedy
1. Clogged carburetor jets.
• Clean
2.
Improperly adjusted main jet
• Adjust
(High speed)
3.
Improperly adjusted jet needle
• Adjust
(Medium speed)
4. Incorrect fuel lever
• Adjust
5. Dirty or clogged air cleaner element
• Clean
6. Clogged fuel tank filler cap or
• Clean
carburetor breather pipe.
7.
Clogged fuel petcock or kinked
• Clean or repair
fuel pipe.
8. Deteriorated fuel.
• Replace
9. Improper oil-gas mixing ratio
• Replace
10. Cracked or broken exhaust pipe
• Replace
(Leakage of exhaust gases).
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