Yamaha YFM400FWA 2000 5GH3-AE1 Service Manual page 376

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
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 ignition coil
Valve train
Improperly adjusted valve clearance
Air filter
Clogged air filter element
Air filter
Clogged air filter element
10 - 2
TRBL
SHTG