Yamaha YFM660RN Service Manual

Contents

9 - 2TRBLSHTGSTARTING FAILURE/HARD STARTING/POOR IDLE SPEEDPERFORMANCE/POOR MEDIUM AND HIGH-SPEED PERFORMANCECOMPRESSION SYSTEMCylinder and cylinder head Loose spark plug Loose cylinder head or cylinder Broken cylinder head gasket Broken cylinder gasket Worn, damaged or seized cylinderValve, camshaft and crankshaft Improperly sealed valve Improperly contacted valve and valve seat Improper valve timing Broken valve spring Seized camshaft Seized crankshaftPiston and piston rings Improperly installed piston ring Worn, fatigued or broken piston ring Seized piston ring Seized or damaged pistonCrankcase and crankshaft Improperly seated crankcase Seized crankshaftValve train Improperly adjusted valve clearance Improperly adjusted valve timingPOOR IDLE SPEED PERFORMANCEPOOR IDLE SPEED PERFORMANCECarburetor Improperly returned starter plunger Loose pilot jet Clogged pilot jet Clogged pilot air jet Improperly adjusted idle speed(Throttle stop screw) Improper throttle cable play Flooded carburetorElectrical system Faulty spark plug Faulty CDI unit Faulty pickup coil Faulty ignition coilValve train Improperly adjusted valve clearanceAir filter Clogged air filter elementPOOR MEDIUM AND HIGH-SPEED PERFORMANCEPOOR MEDIUM AND HIGH-SPEED PERFORMANCERefer to “STARTING FAILURE/HARD STARTING” and “POOR IDLE SPEED PERFORMANCE-VALVE TRAIN”.Carburetor Improper jet needle clip position Improperly adjusted fuel level Clogged or loose main jet Deteriorated or contaminated fuelAir filter Clogged air filter element