![]() Accumulation on ground electrodes and shell areas may be unusually heavy, but may be easily chipped off. This is normal appearance with certain branded fuels. If condition recurs, use colder heat range plug and service plugs more frequently.ħ Scavenger Deposits – Powdery white or yellow deposits are built up on shell, insulator and electrodes. Instead, they melt and form a conductive coating. Normal deposits do not get a chance to blow off. Replace spark plugs.Ħ High Speed Glazing – Insulator has yellowish, varnish-like color, indicating that temperatures suddenly have risen, usually during hard, fast acceleration under heavy load. Also check for over-advanced ignition timing, cooling system malfunction, lean fuel/air mixtures, leaking intake manifold or sticking valves. Check that correct plug heat range is being used. Electrodes are eroded and there is an absence of deposits. After correcting cause, service (clean and re-gap) plugs and reinstall.ĥ Overheating – Insulator is dull white or gray and appears blistered. If, however, only one or two plugs in set are fouled, check for sticking valves or bad ignition leads. Clogged flame arrestor, flooding carburetor, sticky choke or weak ignition components all are probably causes. Such fouled plugs may be serviced (clean and re-gap) and reinstalled.Ĥ Cold Fouling – Dry, black deposits indicate rich fuel mixture or weak ignition. IMPORTANT: New engines or recently overhauled engines may wet foul plugs before normal oil control is achieved with proper break-in procedures. Only engine repairs will permanently relieve oil wet fouling. Worn piston rings, cylinder walls, valve guides or valve stem seals are causes of oil entering combustion chamber. Plug must be replaced.ģ Wet Fouling (Oil Deposits) – Plug becomes shorted by excessive oil entering combustion chamber, usually in engine with many hours of operation. Under certain conditions, severe detonation also can split insulator firing ends. With proper plug servicing (clean and re-gap), this plug can be reinstalled with good results.Ģ Chipped Insulator – Chipped insulator usually results from careless plug re-gapping. This plug shows that plug heat range is compatible with engine, and engine is electrically and mechanically in good running condition. Visually examine the spark plugs as previously outlined, and compare your spark plug to the following information:ġ Normal Condition – Few deposits are present and probably will be light tan or gray in color. ![]()
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