TROUBLESHOOTING - 1C-390-823225--1 1096
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 igni-
tion 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 de-
posits. 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
High Speed Glazing
Insulator has yellowish, varnish-like color, indicating
that temperatures suddenly have risen, usually dur-
ing hard, fast acceleration under heavy load. Normal
deposits do not get a chance to blow off. Instead, they
melt and form a conductive coating. Replace plugs.
If condition recurs, use colder heat range plug and
service plugs more frequently.
72421
Scavenger Deposits
Powdery white or yellow deposits are built up on
shell, insulator and electrodes. This is normal ap-
pearance with certain branded fuels. Accumulation
on ground electrodes and shell areas may be unusu-
ally heavy, but may be easily chipped off. Plugs can
be serviced (clean, file and regap) and reinstalled.
72422
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