In most cases, missing or total lack of spark will be due to dirt, pitting,
or corrosion of the points or a failure of the condenser. Timing may
affected as well by excessive wear. The following procedures should restore
the ignition system to good health:
|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Maintenance of point-type ignition syste..
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First, test for spark. If there is a spark, try replacing the spark plug
since this is the most likely cause of ignition problems. With a spark
present, there could still be ignition system problems but this is much
You may be able to test the points to some extent if you can get to the wire
that connects to the magneto or the STOP switch. A multimeter on the low
ohms scale will the permit you to watch the opening and closing of the points.
If this confirms that the points are operating the condenser could still
be defective, the breaker arm could be sluggish, or the point gap could
be grossly out of adjustment.
To proceed further:
- Remove any trim pieces and the shroud/blower housing to access the
flywheel, magneto, and points assembly under the flywheel.
- Check the flywheel magnet to magneto core air gap. While it is extremely
unlikely that this increased, it is an easy test. The correct value is
usually .015 inches but some engines use other gap spacings. A non-magnetic
feeler gauge is best for this. If it is much larger than specified, adjust
it and test for spark again.
- Remove the flywheel. See the section: Flywheel
- Test the flywheel magnet. No actual strength is usually published but if
it attracts a steel screwdriver from at least a 1/2" distance and seems
strong, the magnet is likely fine. If it is weak (or missing, though this
is mostly a theoretical possibility!), the flywheel will need to be replaced.
- Remove the cover over the breaker points assembly, if any.
- Inspect the points. There should be no serious pitting, corrosion,
evidence of arcing or sparking. Nor should they be welded together!
If any of these problems are present, replace the points and condenser as
well - a bad condenser may be the cause of the points failure it is not
really possible to fully test it.
You can also test for electrical operation of the points using a multimeter
on the low ohms scale while rotating the crankshaft (you will have to use
the blade - careful) or operating the breaker arm manually.
Or better yet, just replace the points and condenser. The cost is minimal
(probably under $5 for a rebuild kit) and you have already done most of
- Note the mounting arrangement and remove the old points and condenser and
install the replacements. Do not tighten the locking screws at this time.
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