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Troubleshooting Guide
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:
Engine won’t turn over:
Cylinder, piston seizure
Crankshaft seizure
Connecting rod small end seizure
Connecting rod big end seizure
Transmission gear or bearing seizure
Kick shaft return spring broken
Kick ratchet gear not engaging
No fuel flow:
No fuel in tank
Fuel tap turned off
Tank cap air vent obstructed
Fuel tap clogged
Fuel line clogged
Float valve clogged
Engine flooded:
Float level too high
Float valve worn or stuck open
Starting technique faulty
(when flooded, kick with the throttle fully
open to allow more air to reach the en-
gine.)
No spark; spark weak:
Spark plug dirty, broken, or maladjusted
Spark plug cap or high tension wiring trou-
ble
Spark plug cap not in good contact
Spark plug incorrect
CDI Unit trouble
Ignition coil trouble
Ignition coil resistor open
Flywheel magneto damaged
Wiring shorted or open
Fuel/air mixture incorrect:
Idle adjusting screw maladjusted
Slow jet or air passage clogged
Air c leaner clogged, poorly sealed, or miss-
ing
Starter jet clogged
Compression Low:
Spark plug loose
Cylinder head not sufficiently tightened
down
Cylinder, piston worn
Piston ring bad (worn, weak, broken, or
sticking)
Piston ring and clearance excessive
Cylinder head gasket damaged
Cylinder head warped
Cylinder base gasket damaged
Read valve damaged
Cylinder nut loose
Poor Running at Low Speed:
Spark weak:
Spark plug dirty, broken, or maladjusted
Spark plug cap or high tension wiring trou-
ble
Spark plug cap shorted or not in good con-
tact
Spark plug incorrect
CDI Unit trouble
Ignition coil trouble
Flywheel magneto damaged
Ignition coil lead or CDI Unit lead not in good
contact
Fuel/air mixture incorrect:
Idle adjusting screw maladjusted
Slow jet or air passage clogged
Air cleaner clogged, poorly sealed, or miss-
ing
Choke plunger stuck open
Float 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
Cylinder, piston worn
Piston ring bad (worn, weak, broken, or
sticking)
Piston ring/land clearance excessive
Cylinder head gasket damaged
Cylinder head warped
Cylinder base gasket damaged
Reed valve damaged
Cylinder nut loose
Other:
CDI Unit trouble
Transmission oil viscosity too high
Brake dragging
Poor Running or No Power at High
Speed:
Firing incorrect:
Spark plug dirty, damaged, or maladjusted
Spark plug cap or high tension wiring dam-
aged
Spark plug cap shorted or not in good con-
tact
Spark plug incorrect
CDI Unit trouble
Ignition coil trouble