Troubleshooting; Starting Failure/Hard Starting; Engine; Fuel System - Yamaha YW125Y 2009 Service Manual

EAS00844

TROUBLESHOOTING

TIP
The following guide for troubleshooting does not cover all the possible causes of trouble. It should be
helpful, however, as a guide to basic troubleshooting. Refer to the relative procedure in this manual
for checks, adjustments, and replacement of parts.

STARTING FAILURE/HARD STARTING

ENGINE

Cylinder and cylinder head
8 Loose spark plug
8 Loose cylinder head or cylinder
8 Damaged cylinder head gasket
8 Damaged cylinder gasket
8 Worn or damaged cylinder
8 Incorrect valve clearance
8 Improperly sealed valve
8 Incorrect valve-to-valve-seat contact
8 Incorrect valve timing
8 Faulty valve spring
8 Seized valve
Piston and piston ring
8 Improperly installed piston ring
8 Damaged, worn or fatigued piston ring
8 Seized piston ring
8 Seized or damaged piston
Air filter
8 Improperly installed air filter
8 Clogged air filter element
Crankcase and crankshaft
8 Improperly assembled crankcase
8 Seized crankshaft

FUEL SYSTEM

Fuel tank
8 Empty fuel tank
8 Clogged fuel tank cap breather hole
8 Deteriorated or contaminated fuel
8 Clogged or damaged fuel hose
Fuel pump
8 Faulty fuel pump
8 Improperly routed hose
Throttle body
8 Deteriorated or contaminated fuel
8 Sucked-in air
STARTING FAILURE/HARD STARTING

ELECTRICAL SYSTEMS

Battery
8 Discharged battery
8 Faulty battery
Fuse(s)
8 Blown, damaged or incorrect fuse
8 Improperly installed fuse
Spark plug
8 Incorrect spark plug gap
8 Incorrect spark plug heat range
8 Fouled spark plug
8 Worn or damaged electrode
8 Worn or damaged insulator
8 Faulty spark plug cap
Ignition coil
8 Cracked or broken ignition coil body
8 Broken or shorted primary or secondary
coil
8 Faulty spark plug lead
Ignition system
8 Faulty ECU
8 Faulty crankshaft position sensor
8 Broken AC magneto rotor woodruff key
Switches and wiring
8 Faulty main switch
8 Faulty engine stop switch
8 Broken or shorted wiring
8 Faulty front, rear or both brake light
switches
8 Faulty start switch
8 Faulty sidestand switch
8 Improperly grounded circuit
8 Loose connections
Starting system
8 Faulty starter motor
8 Faulty starter relay
8 Faulty starting circuit cut-off relay
8 Faulty starter clutch
8-1
TRBL
SHTG