Page 36 - REPOWER REFERENCE GUIDE (2020)

Engine Failure Diagnosis

Wet Fouling (Rust/Water Deposits)
Wet fouling or rust deposits on the spark plugs are caused by water entering the cylinder. Check all cylinders and eliminate the
source of the water intrusion. Water could enter the cylinder from submersion, a leaky engine hatch, a cracked exhaust
manifold, leaky exhaust system gaskets, inadequate riser height for the boat load, improper exhaust system layout/design,
cracked engine block/cylinder head, failed intake manifold, lack of functional exhaust flappers, wildly revving the engine,
exhaust gas condensation, or a failed head gasket. Be sure to root cause the original failure, or an expensive repeat failure will
occur. Change all spark plugs and perform a compression check. Refer to the sections for checking riser height and exhaust
system design for more information.

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Cold Fouling
Dry, black deposits indicate a rich fuel mixture or a weak ignition. A clogged flame arrestor, a flooding engine, a sticky choke,
stuck/dirty injector, bad pressure regulator, vacuum line cracked or missing, bad sensor, wrong ECM/calibration, electrical
short, or weak ignition components all are probable causes. If the spark plug is wet with fuel, perform a compression check and
leak down. If, however, only 1 or 2 plugs in the set are fouled, check for sticking valves or bad ignition leads. After correcting
the cause, service (clean, file, and regap) plugs and reinstall.

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