2000 Yamaha YFM400FWA(M) Factory Service workshop Manual, Page 364Get this manual
STARTING FAILUREHARD STARTINGPOOR IDLE SPEED PERFORMANCEPOOR MEDIUM AND HIGH-SPEED PERFORMANCE COMPRESSION SYSTEM Cylinder and cylinder head Loose spark plug Loose cylinder head or cylinder Broken cylinder head gasket Worn, damaged or seized cylinder Piston and piston rings Improperly installed piston ring Worn, fatigued or broken piston ring Seized piston ring Seized or damaged piston
TRBL SHTG
Valve, camshaft and crankshaft Improperly sealed valve Improperly contacted valve and valve seat Improper valve timing Broken valve spring Seized camshaft Seized crankshaft
POOR IDLE SPEED PERFORMANCE