Polaris RANGER SP 570 Owner's Manual page 119

MAINTENANCE
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 indicates 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 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
or poor fuel quality.
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