7.2
Section 7
Electrical System and Components
Worn:
On a worn plug, the center electrode will be
rounded and the gap will be greater than the specified
gap. Replace a worn spark plug immediately.
Overheated:
Chalky, white deposits indicate very
high combustion temperatures. This condition is
usually accompanied by excessive gap erosion. Lean
carburetor settings, an intake air leak, or incorrect
spark timing are normal causes for high combustion
temperatures.
Normal:
A plug taken from an engine operating under
normal conditions will have light tan or gray colored
deposits. If the center electrode is not worn, a plug in
this condition could be set to the proper gap and
reused.
Carbon Fouled:
Soft, sooty, black deposits indicate
incomplete combustion caused by a restricted air
cleaner, over rich carburetion, weak ignition, or poor
compression.
Wet Fouled:
A wet plug is caused by excess fuel or oil
in the combustion chamber. Excess fuel could be
caused by a restricted air cleaner, a carburetor
problem, or operating the engine with too much
choke. Oil in the combustion chamber is usually
caused by a restricted air cleaner, a breather
problem, worn piston rings, or valve guides.
