Troubleshooting Guide; Engine Is Hard To Start Or Does Not Start - Yamaha YTZ250S 1986 Service Manual

II
APPENDICES
TROUBLESHOOTING GUIDE
Engine is hard to start or does not start.
Ignition System
Possible Cause
Remedy
1. Spark plug is wet.
• Clean or replace
2. Ignition coil is faulty.
• Replace
3.
C.D.I. unit is faulty.
• Replace
4. C.D.I. magneto is faulty (Pulser
• Replace
coil, source coil)
5. Ignition timing is incorrect.
• Adjust
6.
Wire is broken, shorted or dis- • Repair, replace or connect
connected.
7.
Engine stop switch is shorted.
• Repair or replace
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 leaks passing cylinder
• Replace (or repair)
head gasket. (Head is distoreted) .
4. Crankshaft side oil seal is faulty.
• Replace
5. Air leaks through crankcase
• Repair
sealing surfaces.
Air/Fuel System
Possible Cause Remedy
1. Carburetor pilot jet is clogged.
• Clean
2. Fuel petcock or pipe is clogged .
• Clean
3. Float valve is faulty.
• Replace (remove gasoline from
(Float height is too high or too low.) crankcase)
4. Reed valve is broken or deformed.
• Replace
5. Fuel tank filler cap or carburetor
• Clean
brather pipe is clogged.
6. Air screw is improperly adjusted.
• Adjust
7. Fuel is deteriorated.
• Repalce
8. Oil-gas mixing ratio is incorrect.
• Replace
9.
Air leakes through carburetor joints. • Retighten or replace gasket
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