Fuel system
Fuel tank
- Empty
- Clogged fuel filter
- Clogged fuel strainer
- Clogged fuel tank drain hose
- Clogged roll-over valve
- Clogged roll-over valve breather hose
- Deteriorated or contaminated fuel
- Fuel cock
- Clogged fuel hose
Carburetor
- Deteriorated or contaminated fuel
- Clogged pilot jet
- Clogged pilot air passage
- Sucked-in air
- Deformed float
- Worn needle valve
- Improperly sealed valve seat
- Improperly adjusted fuel level
- Improperly set pilot jet
- Clogged starter jet
- Faulty starter plunger
- Improperly adjusted starter cable
Air filter
- Clogged air filter element
Fuel pump
- Faulty fuel pump
- Faulty relay unit (fuel pump relay)
Electrical system
Spark plug
- Improper plug gap
- Worn electrodes
- Wire between terminals severed
- Improper heat range
- Faulty spark plug cap
Ignition coil
- Broken or shorted primary / secondary
- Faulty spark plug lead
- Broken body
Full-transistor system
- Faulty ignitor unit
- Faulty pickup coil
Switch and wiring
- Faulty main switch
- Faulty engine stop switch
- Broken or shorted wiring
- Faulty neutral switch
- Faulty start switch
- Faulty sidestand switch
- Faulty clutch switch
Starter motor
- Faulty starter motor
- Faulty starter relay
- Faulty relay unit (starting circuit cut-off relay)
- Faulty starter clutch
Compression system
Cylinder and cylinder head
- Loose spark plug
- Loose cylinder head or cylinder
- Faulty cylinder head gasket
- Worn, damaged or seized cylinder
- Improperly sealed valve
- Improper valve-to-valve seat contact
- Improper valve timing
- Faulty valve spring
Piston and piston ring
- 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