1999-2004 Honda TRX400EX FourTrax Service Manual, Page 112Get this manual
CYLINDERPISTON
TROUBLESHOOTING
Compression too low, hard starting or poor performance at low speedLeaking cylinder head gasketWornstuck or broken piston ring Worn or damaged cylinder and piston
Compression too high, overheating or knocking Excessive carbon built-up on piston head or combustion chamber