195
CHAPTER 9 Two-Stroke Engine Troubleshooting and Evaluation
Copyright Goodheart-Willcox Co., Inc.
the end of the ground wire and the other lead to
the metal of the engine block. See Figure 9-25.
When the stop switch is in the ON (RUN) posi-
tion, there should be no continuity across the
switch. When the stop switch is in the OFF
(STOP) position, there should be continuity.
“Is this coil the correct coil for the engine?”
Record both the ignition coil part number and
the flywheel part number. Compare these num-
bers with the part numbers in an illustrated
parts list for this engine. Sometimes, a known
good coil is substituted for a coil that is sus-
pected of being bad. The replacement coil may
look identical to the EOM coil but with different
part numbers. A different part number means
that the replacement coil might not provide a
spark, or it may provide a spark at the wrong
time.
Check the armature air gap with the correct
thickness gauge or feeler gauge. In Figure 9-26,
a gauge of the correct thickness is inserted
between the flywheel and the ignition coil. The
gauge should fit snug, neither tight nor loose. If
necessary, the coil mounting fasteners can be
loosened so the coil can be repositioned to set
the correct air gap. After the correct air gap is
set, the mounting fasteners should be tightened
to the correct torque.
Measure and record the ignition coil’s pri-
mary and secondary windings resistances. With
the ground wire disconnected from the ignition
coil, measure the resistance from the kill tab to
the engine ground. See Figure 9-27. Compare
Kill tab
Ground wire
disconnected
Goodheart-Willcox Publisher
Figure 9-24. To isolate the ignition coil from the
stop switch, disconnect the ground wire at the
coil. Make sure the connector does not touch
the coil’s kill tab when the rewind starter is
reinstalled.
Switch on—
no continuity
Lead touches
engine ground
Lead connected
to switch
Goodheart-Willcox Publisher
Figure 9-25. The stop switch grounds the pri-
mary winding to stop the spark. When the stop
switch is in the OFF position, there should be
continuity through the switch. In the ON (RUN)
position, the switch should be open.
Ignition coil Curved armature
air gap gauge
Flywheel
Goodheart-Willcox Publisher
Figure 9-26. A gauge of the correct thickness or
a feeler gauge is used to determine the armature
air gap. Make a note if the gauge is snug, very
tight, or loose.