Cub Cadet MTD 70 Series - Manual (Page 91)

Ignition System
85
The module
The coil in this ignition system is an inductive discharge magneto, contained in a single module.
• The inductive discharge magneto has a two leg design.
• The magneto is energized by the passing of a pair of magnets mounted in the flywheel.
• Ignition timing is set by the location of the flywheel in relation to the crankshaft. Proper timing is main-
tained by a steel key.
Normal performance of the coil is to produce at least 10,000 volts at starter-rope pull-through speed.
The presence or absence of strong spark, with the stop switch known to be good, is generally enough to identify
the ignition coil as good or bad. Resistance readings may help confirm the source of the failure, but are generally
meaningless because they only measure a small part of the module.
NOTE: Presence of a weak spark maybe the result of an improper air gap. The air gap space should be 0.008”
- 0.016” (0.2 - 0.4 mm).
Simple spark-testers are readily available and inexpensive. Thexton Part # 404 is available from a variety of
retailers, and similar units are available from other manufacturers.
NOTE: If the complaint is that the engine quits run-
ning when it gets warm, the ignition module
should be tested with the engine at normal
operating temperature.
NOTE: At operating speed, the ignition should pro-
duce voltage approaching 12,000.
NOTE: At pull-over speed (~ 600 RPM), voltage
should be at least 10,000V.
NOTE: Flash-over voltage will vary with spark plug
condition and gap.
NOTE: Pull-over speed may vary from operator to
operator.
NOTE: Failure of the magnets in the flywheel is
exceedingly rare. To test the magnets, sim-
ply hold an item made of ferrous metal roughly 1/4” (0.635cm) away from the magnets in the flywheel.
It should be drawn to the flywheel. A wrench or screwdriver is suitable for this test.
Figure 7.10