8.2
Section 8
Electrical System and Components
Inspection
Inspect the spark plug when 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:
Worn: On a worn plug, the center electrode will be
rounded and the gap will be greater than the specifi ed
gap. Replace a worn spark plug immediately.
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: So , 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,
or internal engine wear.
Overheated: Chalky, white deposits indicate very
high combustion temperatures. This condition is
usually accompanied by excessive gap erosion. Lean
carburetor se ings, an intake air leak, or incorrect
spark timing are normal causes for high combustion
temperatures.
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