196
Two-Stroke Engines
Copyright Goodheart-Willcox Co., Inc.
this measurement with the manufacturer’s spec-
ification for the primary resistance.
Measure the resistance from the engine
ground to the output connector of the high-ten-
sion lead. See Figure 9-28. Compare this
measurement with the specification for the sec-
ondary resistance.
A simple test for measuring the strength of
the flywheel magnets is to place the tip of a
medium-sized flat head screwdriver on the mag-
nets. The magnets should be strong enough to
hold the screwdriver at a tangent to the mag-
nets. See Figure 9-29.
Once the flywheel has been removed cor-
rectly, inspect the flywheel key to see if it has
been sheared. Some flywheels have an inte-
grated key. Figure 9-30 shows an integrated key
that was sheared. If the flywheel key is sheared
or deformed, the engine could have a spark, but
the timing would be incorrect. The key sets the
timing for the engine by orienting the flywheel
correctly in relation to the crankshaft. The key
NOTE
Because of the electronic circuits contained
inside some coils, the primary resistance
may not be measured. There may be an open
between the primary winding and ground.
shears when the flywheel rotates in relation to
the crankshaft. The shaft stops and the flywheel
keeps rotating.
Finish the inspection of the flywheel by look-
ing for cracked or broken fins. Check to see if
the flywheel is loose or if it is cracked or warped.
Read and follow the service manual before
testing the ignition system. Some two-stroke
engines have electronic ignition system com-
ponents that could be damaged if tested incor-
rectly. The engine manufacturer provides
Ohm’s setting Kill tab Engine ground
Goodheart-Willcox Publisher
Figure 9-27. Measure primary resistance from
the coil’s kill tab to the engine ground. The coil’s
mounting screw typically connects the coil to the
engine ground.
Spark plug
connector Engine ground
Goodheart-Willcox Publisher
Figure 9-28. Measure the resistance for the
secondary winding from the engine ground to the
metal connector inside the spark plug boot.
Goodheart-Willcox Publisher
Figure 9-29. An indicator of the strength of
the flywheel magnets is when they can hold a
medium-sized flat head screwdriver at a tangent
to the magnets.