Spark Plug Heat Range - Honda CB350 Repair Manual

38 TUNE—UP
Normal Oil—fouled
Overheated Core—bridged
4. Remove the spark plugs and exam—
ine them for the following conditions:
a. A wet, black, and shiny deposit on
the plug base, electrodes, and ceramic
tip (around the positive electrode) in—
dicates an oil—fouled plug caused by
worn rings and pistons, loose valves,
bad valve guide seals, weak spark,
faulty ignition circuit, improper points
gap, dirty points, improper timing
(overly retarded), weak coil, or too cold
a plug heat range;
b. A smooth, sooty, jet—black deposit
indicates an excessively rich gas mix—
ture, long periods of engine idling, or
too cold a plug;
c. A very light brown, dry, blistered,
or glassy—looking deposit indicates an
overheated plug. This may be accom—
panied by cracks in the ceramic tip and
is caused by an overly lean air—fuel
mixture, an excessively high operating
temperature, improper valve seating,
advanced ignition timing, or a plug
which is too hot. The deposit becomes
a conductor when hot and causes irreg—
ular firing, especially at high rpm;
d. A plug with a milky or tan deposit
indicates a well—balanced ignition and
Splash—fouled: caused byinstalla—
tion of new plugs after a long—
delayed tune—up
mixture. This type of deposit will not
adversely affect performance if kept to
a minimum, but no type of deposit
should be allowed to build up. Both of
the plugs should burn the same way.
When in doubt about the condition of
your plugs, it's best to replace them.
This is the best rule for efficiency.
5. Plugs with electrodes worn or
rounded either through excessive heat or
normal wear must be replaced. Also, re—
place any plug if the ceramic insulator
around the center electrode is cracked.
Spark Plug Heat
Range
Plug heat range can and should be
varied to suit individual riding habits.
The standard plug should provide ade—
quate performance for normal riding.
Stop—and—go riding, especially at urban
speeds, may require a plug one heat
range hotter. This will be added insur—
ance against plug fouling or loading up in
traffic. Under no circumstances should a