SERVICE MANUAL NUMBER 24
TROUBLESHOOTING
Wet Fouling (Oil Deposits)
Plug becomes shorted by excessive oil entering combustion chamber, usually in engine with
many hours of operation. Worn piston rings, cylinder walls, valve guides or valve stem seals
are causes of oil entering combustion chamber. Only engine repairs will permanently relieve
oil wet fouling.
IMPORTANT: New engines or recently overhauled engines may wet foul plugs before
normal oil control is achieved with proper break-in procedures. Such fouled plugs
may be serviced (clean, file and regap) and reinstalled.
72420
Cold Fouling
Dry, black deposits indicate rich fuel mixture or weak ignition. Clogged flame arrestor,
flooding carburetor, sticky choke or weak ignition components all are probable causes. If,
however, only one or two plugs in set are fouled, check for sticking valves or bad ignition
leads. After correcting cause, service (clean, file and regap) plugs and reinstall.
72421
Overheating
Insulator is dull white or gray and appears blistered. Electrodes are eroded and there is an
absence of deposits. Check that correct plug heat range is being used. Also check for
over-advanced ignition timing, cooling system malfunction, lean fuel/air mixtures, leaking
intake manifold or sticking valves. Replace spark plugs.
72421
Index
90-861327--1
OCTOBER 1999
Page 1C-3
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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