Compression System; Poor Idle Speed Performance - Yamaha YQ50 Service Manual

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
• Clogged or loose pilot jet
• Clogged pilot air jet
• Improperly adjusted idle speed ( throttle stop screw)
• Improper throttle cable play
• Flooded carburetor
STARTING FAILURE/HARD STARTING/
POOR IDLE SPEED PERFORMANCE
Crankcase and crankshaft
• Improperly seated crankcase
• Improperly sealed crankcase
(damaged oil seal)
• Seized crankshaft
Reed valve
• Deformed reed valve stopper
• Improperly seated reed valve
• Loose intake manifold
• Broken gasket
• Broken reed valve
9-2
TRBL
SHTG