Yamaha TW125 1999 Service Manual page 277

EAS00844
NOTE:
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 PROBLEMS
ENGINE
Cylinders and cylinder head(-s)
S Loose spark plug
S Loose cylinder head
S Damaged cylinder head gasket
S Worn or damaged cylinder
S Incorrect valve clearance
S Incorrectly sealed valve
S Incorrect valve-to-valve-seat contact
S Incorrect valve timing
S Faulty valve spring
S Seized valve
Pistons and piston rings
S Incorrectly installed piston ring
S Damaged, worn or fatigued piston ring
S Seized piston ring
S Seized or damaged piston
Air filter
S Incorrectly installed air filter
S Clogged air filter element
Crankcase and crankshaft
S Incorrectly assembled crankcase
S Seized crankshaft
ELECTRICAL SYSTEMS
Battery
S Faulty battery
S Discharged battery
Fuse
S Blown, damaged or incorrect fuse
S Incorrectly installed fuse
Spark plug
S Incorrect spark plug gap
S Incorrect spark plug heat range
S Fouled spark plug
S Worn or damaged electrode
S Worn or damaged insulator
S Faulty spark plug cap
Ignition coil
S Damaged ignition coil
S Broken or shorted primary or secondary coils
S Faulty spark plug lead
STARTING PROBLEMS
TROUBLESHOOTING
FUEL SYSTEM
Fuel tank
Fuel cock
Carburetors
Ignition system
Switches and wiring
Starting system
8-1
S Empty fuel tank
S Clogged fuel filter
S Clogged fuel tank breather hole
S Deteriorated or contaminated fuel
S Clogged or damaged fuel hose
S Deteriorated or contaminated fuel
S Clogged pilot jet
S Clogged pilot air passage
S Sucked-in air
S Damaged float
S Worn needle valve
S Incorrectly installed needle valve seat
S Incorrect fuel level
S Incorrectly installed pilot jet
S Clogged starter jet
S Faulty starter plunger
S Incorrectly adjusted starter cable
S Faulty CDI unit
S Faulty pickup coil
S Faulty main switch
S Faulty engine stop switch
S Broken or shorted wiring
S Faulty neutral switch
S Faulty start switch
S Faulty sidestand switch
S Faulty clutch switch
S Incorrectly grounded circuit
S Loose connections
S Faulty starter motor
S Faulty starter relay
S Faulty neutral relay
S Faulty starter clutch
TRBL
SHTG