7.2
Section 7
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.
Carbon Fouled: So , sooty, black deposits indicate
incomplete combustion caused by a restricted air
cleaner, over-rich fuel mixture, weak ignition, or poor
compression.
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.
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 or rich air/fuel ratio.
Oil in the combustion chamber is usually caused by
a restricted air cleaner, a breather problem, or worn
piston rings, cylinder walls or valve guides.
Overheated: Chalky, white deposits indicate very high
combustion temperatures. This condition is usually
accompanied by excessive gap erosion. Lean air/fuel
ratio, an intake air leak, or incorrect spark timing are
normal causes for high combustion temperatures.
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