Trbl Shtg; Compression System; Poor Idle Speed Performance; Poor Medium And High-Speed Performance - Yamaha YFM250RX 2008 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
Valve and camshaft
• Improperly sealed valve
• Improperly contacted valve and valve seat
• Improper valve timing
• Broken valve spring
• Seized camshaft
EBS00538

POOR IDLE SPEED PERFORMANCE

POOR IDLE SPEED PERFORMANCE
Carburetor
• Improperly returned choke
• Loose or clogged pilot jet
• Loose or clogged pilot air jet
• Improperly adjusted idle speed
(throttle stop screw)
• Improper throttle cable play
• Flooded carburetor
Intake manifold
• Loosen carburetor joint
EBS00539

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
Piston and piston rings
• Improperly installed piston ring
• Worn, fatigued or broken piston ring
• Seized piston ring
• Seized or damaged piston
Crankcase and crankshaft
• Improperly seated crankcase
• Seized crankshaft
Valve train
• Improperly adjusted valve clearance
• Improperly adjusted valve timing
Electrical system
• Faulty battery
• Faulty CDI unit
• Faulty pickup coil
• Faulty ignition coil
Valve train
• Improperly adjusted valve clearance
Air filter
• Clogged air filter element
• Loosen air filter joint
Air filter
• Clogged air filter element
8-2
TRBL
SHTG