Page 38 - REPOWER REFERENCE GUIDE (2020)

Engine Failure Diagnosis

Preignition Damage
Preignition damage is caused by excessive high temperatures. The center electrode melts first, followed by the ground
electrode. Normally, the insulators are white, but may be dirty if the plug has been misfiring. Check for the correct plug heat
range, incorrect rotor location, lean fuel mixture, incorrect fuel used, malfunctioning cooling system, leaking intake manifold, or
lack of lubrication. Examine the spark plug gasket for crush or the seat for witness marks to verify proper torque was applied.
Perform a compression check and leak down on all cylinders. Replace the spark plugs.

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Reversed Coil Polarity

Concave erosion of the ground electrode is an indication of reversed polarity. The center electrode will show only normal wear.
The engine will misfire and idle rough. To correct, reverse the primary coil leads. Replace the spark plugs.

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Splashed Deposits
Spotted deposits, which sometimes occur after long delayed tune‑up, accumulate after a long period of misfiring. When normal
combustion temperatures are restored, upon the installation of the new plugs, the deposits loosen from the top of the piston
and the cylinder head and are thrown against the hot insulator. Service (clean, file, and regap) plugs and reinstall.

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