- Battery voltage low
- Spark plug dirty, broken, or maladjusted
- Stick coil wiring trouble
- Stick coil not in good contact
- Spark plug incorrect
- IC igniter trouble
- Pickup coil trouble
- Stick coil trouble
Fuel/air mixture incorrect:
- Pilot screw maladjusted
- Pilot jet, or air passage clogged
- Air bleed pipe bleed holes clogged
- Pilot passage clogged
- Air cleaner clogged, poorly sealed, or missing
- Starter plunger stuck open
- Fuel level in carburetor float bowl too high or too low
- Fuel tank air vent obstructed
- Fuel cut valve won’t fully open (check fuel cut valve and IC igniter)
- Carburetor holder loose
- Air cleaner duct loose
- Air cleaner О-ring damaged
- Fuel pump trouble
- Fuel pump relay trouble
- Fuel filter clogged
Compression low:
- Spark plug loose
- Cylinder head not sufficiently tightened down
- No valve clearance
- Cylinder, piston worn
- Piston ring bad (worn, weak, broken, or sticking)
- Piston ring/groove clearance excessive
- Cylinder head warped
- Cylinder head gasket damaged
- Valve spring broken or weak
- Valve not seating properly (valve bent, worn, or carbon accumulation on the seating surface)
Other:
- IC igniter trouble
- Carburetor not synchronizing
- Carburetor vacuum piston doesn’t slide smoothly Carburetor vacuum piston diaphragm damage Engine oil viscosity too high
- Drive train trouble
- Brake dragging
- Air suction valve trouble
- Vacuum switch valve trouble