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The normal insulator tip is gray, tan or light brown. There will be few combustion deposits.
The electrodes are not burned or eroded. This indicates the proper type and heat range for the
engine and the service.
NOTE: The tip should not be white. A white insulator tip indicates overheating, caused by use of an
improper spark plug or incorrect carburetor/throttle body adjustments.
Wet Fouled Plug
The wet fouled insulator tip is black. A damp oil film covers the firing end. There may be a
carbon layer over the entire nose. Generally, the electrodes are not worn. General causes of
fouling are excessive oil, use of non-recommended oil, improper use of the choke, or incor-
rect carburetion adjustments.