Compression System; Poor Idle Speed Performance; Poor Medium And High-Speed Performance - Yamaha YXR70FX 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
Valves, camshaft and crankshaft
• Improperly sealed valve
• Improperly contacted valve and valve seat
• Improper valve timing
• Broken valve spring
• Seized camshaft
• Seized crankshaft
EBS00538

POOR IDLE SPEED PERFORMANCE

POOR IDLE SPEED PERFORMANCE
Throttle body
• Damaged or loose throttle body joint
• Improper throttle cable play
• Flooded throttle body
Electrical system
• Faulty spark plug
• Faulty ECU
• Faulty crankshaft position sensor
• Faulty ignition coil
EBS00539

POOR MEDIUM AND HIGH-SPEED PERFORMANCE

POOR MEDIUM AND HIGH-SPEED PERFORMANCE
Refer to "STARTING FAILURE/HARD STARTING" and "POOR IDLE SPEED PERFORMANCE".
Fuel pump
• Faulty fuel pump
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
Valve train
• Improperly adjusted valve clearance
Air filter
• Clogged air filter element
Air filter
• Clogged air filter element
10 - 2
TRBL
SHTG
10