Compression System; Poor Idle Speed Performance; Poor Medium And High-Speed Performance - Yamaha YFM660FP Service Manual

STARTING FAILURE/HARD STARTING/POOR IDLE SPEED
PERFORMANCE/POOR MEDIUM AND HIGH-SPEED PERFORMANCE

COMPRESSION SYSTEM

Cylinder and cylinder head
Loose spark plug
●
Loose cylinder head or cylinder
●
Broken cylinder head gasket
●
Broken cylinder 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
●

POOR IDLE SPEED PERFORMANCE

POOR IDLE SPEED PERFORMANCE
Carburetor
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 carburetor
●

POOR MEDIUM AND HIGH-SPEED PERFORMANCE

POOR MEDIUM AND HIGH-SPEED PERFORMANCE
Refer 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 fuel
●
Valve, camshaft and crankshaft
Improperly sealed valve
●
Improperly contacted valve and valve seat
●
Improper valve timing
●
Broken valve spring
●
Seized camshaft
●
Seized crankshaft
●
Electrical system
Faulty spark plug
●
Faulty CDI unit
●
Faulty pickup coil
●
Faulty charging/rotor rotation direction coil
●
Faulty ignition coil
●
Valve train
Improperly adjusted valve clearance
●
Air filter
Clogged air filter element
●
Air filter
Clogged air filter element
●
10 - 2
TRBL
SHTG