Spark Plugs - Johnson SKEE-HORSE 25-201R Service Manual

7-8
YELLOW
4TH FIN
COUNTER-
FLYWHEEL
KEYWAY
Figure 7-24
Figure 7-25
Figure 7-26
/
BOSS
17144
29156
j.
Reassemble remaining items in reverse order of disassembly.
k. When this procedure is followed, engine is timed correctly without
further adjustment. To recheck, use an automotive timing light,
either a 12 volt or 110 volt model. One of the cooling fins on the
flywheel out from the keyway has a small raised boss. The fourth
fin, counterclockwise after the fin with boss, should be painted
yellow
(if
paint has deteriorated, repaint). With the engine oper-
ating at idle speed (1300 to 1600 rpm), this painted mark can be
seen in center of timing hole when light is focused there. Timing
slot is approximately 7/8 inch long, and is located above the man-
ual starter (at the 12
0'
clock position) in the outer fan housing
(see Figure 7-24).
SPARK PLUGS
The condition and appearance of spark plugs taken from an engine may
be a guide to the type and source of engine trouble. Proper spark plug
heat range and normal engine conditions will produce powdery deposits
of a rust brown to grayish or tan color on the firing end of the insulator,
and a minor degree of electrode wear (see Figure 7-25). Highly leaded
fuels may produce white to yellowish powdery deposits on the firing end
of the spark plug. These deposits will not interfere with normal spark
plug performance if plugs are cleaned at regular service intervals. See
page 4-3 for a discussion on spark plug heat range.
a.
If
the insulator tip is an exceptionally light tan or whitish color, or
the center electrode burned away, the heat range may be too hot
(see Figure 7-26).
b. A dark, black or sootish coloration, or wet appearance, ordinarily
indicates the heat range as being too cold (see Figure 7-27). Black,
sooty deposits on the entire firing end of the sparK plug result
from incomplete combustion due to an overly rich air-fuel mix-
ture, incorrect choke setting, or misfiring caused by faulty ignition
components.
c. A definite white coloration may indicate the presence of moisture
in the combustion chamber. Similar deposits are caused by pre-
ignition.
d. Oil fouling deposits wet, sludgy deposits and is a result of mis-
firing or of excessive oil in the fuel mixture (see Figure 7-28).
e. Burned or overheated spark plugs may be identified by a white,
burned, or blistered insulator nose, and badly eroded electrodes.
Excessive deposits in the combustion chamber, a lean fuel mixture
or improperly installed spark plugs can cause overheating.
17150
Figure 7-27
Figure 7-28