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8.2
Section 8
Electrical System and Components
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.
Inspection
Inspect each spark plug as it is removed from the
cylinder head. The deposits on the tip can be an
indication of the general condition of the engine and/or
adverse operating conditions.
Normal and fouled plugs are shown in the following
photos:
Carbon Fouled: Soft, sooty, black deposits indicate
incomplete combustion caused by a restricted air
cleaner, overrich carburetion, weak ignition, or poor
compression.
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.
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.