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18-2 APPENDIX
Troubleshooting Guid e
NOTE
○
This is not an exhaustive list, giving every
possible cause for each problem listed. It
is meant simply as a rough guide to assist
the troubleshooting for some of the more
common difficulties.
Engine Doesn’t Start, Starting Difficulty:
Starter motor not rotating:
Neutral switch trouble
Starter motor trouble
Battery voltage low
Relays not contacting or operating
Starter button not contacting
Wiring open or shorted
Ignition switch trouble
Engine stop switch trouble
Fuse blown
Starter motor rotating but engine doesn’t
turn over:
Starter motor clutch trouble
Recoil starter not operating
Recoil starter spring broken
Recoil starter pawl not engaging
Engine won’t turn over:
Valve seizure
Rocker arm seizure
Cylinder, piston seizure
Crankshaft seizure
Connecting rod small end seizure
Connecting rod big end seizure
Transmission gear or bearing seizure
Camshaft seizure
No fuel flow:
Fuel tank air vent obstructed
Fuel tap clogged
Fuel line clogged
Float valve clogged
Fuel pump damaged or circuit open/short
Engine flooded:
Fuel level too high
Float valve worn or stuck open
Starting technique faulty
(When flooded, crank the engine with the
throttle
fully opened to allow m ore air to reach the
engine.)
Fuel/air mixture incorrect:
Pilot screw and/or idle adjusting screw mal-
adjusted
Pilot jet or air passage clogged
Air cleaner clogged, poorly sealed, or miss-
ing
Starter jet clogged
No spark; spark weak:
Spark plug dirty, broken, or maladjusted
Spark plug cap or spark plug lead trouble
Spark plug cap not in good contact
Spark plug incorrect
Crankshaft sensor trouble
Igniter trouble
Ignition coil trouble
Battery voltage low
Ignition or engine stop switch shorted
Wiring shorted or open
Fuse blown
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 gasket damaged
Cylinder head warped
Valve spring broken or weak
Valve not seating properly (valve bent,
worn, or carbon accumulation on the
seating surface)
Compression release cam (K.A.C.R.) sticks
open (Engine stalls when moving off)
Poor Running at Low Speed:
Spark weak:
Spark plug dirty, broken, or maladjusted
Spark plug cap or spark plug lead trouble
Spark plug cap shorted or not in good con-
tact
Spark plug incorrect
Igniter trouble
Crankshaft sensor trouble
Ignition coil trouble
Battery voltage low
Fuel/air mixture incorrect:
Pilot screw and/or idle adjusting screw mal-
adjusted
Pilot jet or air passage clogged
Starter plunger stuck open
Air cleaner clogged, poorly sealed, or miss-
ing
Fuel level too high or too low
Fuel tank air vent obstructed
Carburetor holder loose
Air cleaner duct loose
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