Polaris Ranger 400 HO Owner's Manual page 67

MAINTENANCE
Spark Plugs
Spark Plug Inspection
Normal Plug
The normal insulator tip is gray, tan or light brown. There will be few
combustion deposits. The electrodes are not burned or eroded. This indi-
cates the proper type and heat range for the engine and the service.
The tip should not be white. A white insulator tip indicates overheating,
caused by use of an improper spark plug or incorrect carburetion adjust-
ments.
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 incorrect throt-
tle body/carburetor adjustments.
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