8.2
Section 8
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.
Inspection
Inspect the spark plug as soon as it is removed from
the cylinder head. The deposits on the tip are an
indication of the general condition of the piston rings,
valves, and carburetor.
Normal and fouled plugs are shown in the following
photos.
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, overrich 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,
or internal engine wear.
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