Honda CB350 Repair Manual page 39

34 TUNE—UP
and side electrodes. Wash the plug thor—
oughly in a solvent after cleaning. If a
commercial "plug cleaner" (sandblaster)
is used, note that oily or oil—fouled plugs
should not be cleaned with these devices
as the oil will catch and hold the abrasive
cleaning particles.
3. Check the condition of the center
and side electrodes. Replace the plug if
they are worn (rounded or partially
melted). Use a points file to square off
the center electrode.
4. Replace the plug if there is a green—
ish tint on the electrodes indicating ex—
tremely high operating temperatures.
Setting plug gap
5. Check the plug gap with a wire—type
feeler gauge. Proper gap for all models is
0.024—0.028 in. (0.6—0.7 mm). Adjust the
gap, if necessary, by bending the side
electrode. The feeler gauge should be a
slip fit in a properly gapped plug.
NOTE: Although a blade—type feeler
gauge can be used to gap new spark
plugs, used plugs should be gapped
with a wire—type feeler gauge as
shown.
WRONG RIGHT
Used spark plugs should be gapped with a wire—
type feeler gauge, as shown (right)
6. If new plugs are being fitted, be
sure that they are the correct heat range
and reach. The latter is very important. If
the reach is too short, the spark will be
partially shielded by the spark plug hole
with adverse effects on the ignition pro—
cess. In addition, the carbon will cover
the lower plug hole threads, making it
difficult or impossible to fit the correct
plug later.
Heat range may be varied somewhat to
suit riding conditions. The recom—
mended heat range is suitable for average
use.
Te
Be sure that the correct reach plug (center) is fitted
Hot type Medium type Cold type
Spark plug heat rangeis a function of the length of
the center electrode insulation
B—6 H
Thread length
E 19.0 mm
C» J H 12.7 mm
g + No marking
A 12.5 imm
B 9.5 mm
— Heat value
Large number ....... Cold type
Small number ...... Hot type
——— Thread diameter
A 18 mm
B 14 mm
D 12 mm
c 10 mm
NGK spark plug interpretation code