NotTaR of small Gasoline Engines and Rotary Lawn Mowers : About Wico magnetos                     
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About Wico magnetos

These are separate units (not part of the flywheel assembly) and may be found on larger (usually horizontal crank) engines.

(From: Al Savage (asavage@iname.com).).

The design is such that it uses an impulse spring to fire at low speed (less than 10 rpm, yes 10). It does a complex wind spring/release spring action until the engine fires. Other than the straightforward "replace the points/condenser" maintenance, I don't think I ever had to have the mechanical section apart, they're that reliable. I do think I had to clean up a couple of them, and relube them though.

If you rotate the engine by hand (careful!) you should hear the impulse spring release, with a very audible bang. With the high tension lead hooked to your spare-plug-on-the-head, you should be able to have at least 3/8" spark; less is probably not enough.

If you don't hear that loud bang from the mag, while very slowly cranking the engine by hand (two turns per bang on that impulse unit), you probably have a mechanical problem. If you hear the bang, but can't get the mag to fire repeatably, I'd refurb the points and condenser. It's a bit tricky, and I haven't even seen one in 15 years, much less worked on one in twenty, but there are many still in service and parts should be readily available.

Oh, yes. I worked most of my teen years in small engine repair. So I DO know whereof I speak. On that vintage equipment, anyway.