Poor Medium And High Speed Performance; Fuel System; Electrical System; Compression System - Yamaha YQ50 Service Manual

POOR MEDIUM AND HIGH SPEED PERFORMANCE/

POOR MEDIUM AND HIGH SPEED PERFORMANCE

FUEL SYSTEM

Fuel tank
• Clogged fuel filter
• Deteriorated fuel or fuel containing water or
foreign material
• Clogged fuel tank cap
Fuel cock
• Clogged fuel hose
Air cleaner
• Clogged air cleaner

ELECTRICAL SYSTEM

Spark plug
• Improper plug gap
• Worm electrodes
• Wire between terminals broken
• Improper heat range
• Faulty spark plug cap

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

FAULTY AUTOMATIC (V-BELT TYPE)

SCOOTER DOES NOT MOVE WHILE ENGINE IS OPERATING.

V-belt
• Worn, damaged or slipped v-belt
Primary sheave
• Worn or damaged cam plate
• Worn or damaged slider bushing

CLUTCH-OUT FAILURE

Primary sheave
• Seized primary sliding sheave and collar
FAULTY AUTOMATIC
Carburetor
• Deteriorated fuel, fuel containing water or
foreign material
• Sucked-in air
• Deformed float
• Groove-worm needle valve
• Improperly sealed valve seat
• Improperly set clip position of jet needle
• Improperly adjusted fuel level
• Clogged or loose main jet
• Clogged or loose main nozzle
CDI unit system
• Faulty CDI unit
• Faulty source coil
• Faulty pick-up coil
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
Secondary sheave
• Broken compression spring
• Pealed lining from clutch shoe
• Worn spline of clutch housing
Secondary sheave
• Broken or fatigued clutch shoe spring
9-3
TRBL
SHTG