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Charlie discovered that Impulse Couplings are trouble waiting to happen. Why you would have impulse couplings on both mags when only one is ON during start is a mystery. I don't know about Charlie's mags but on my airplane (Bendex S-1200 mags) there is no impulse coupling but the left mag does have a second set of breaker points that are "retarded" to about 5 DBTDC. I have also wired in a Starter Vibrator whose function is to provide an alternating (pulsating) current to the magneto's primary winding during starting. During starting the retard points and starter vibrator are used to deliver multiple  sparks beginning at 5 DBTDC and continuing through TDC. This system is also known as "shower of sparks" and has been 100% effective in my plane. The bad news is that you can't hand prop a start, not that I would ever try on a 540. The good news is that prop is less dangerous when the plane is parked.

If I were Charlie I would be asking why there is a second impulse coupled magneto and who put it there (I doubt it is in the parts list for that engine). I would seem that the problem was caused by a part that wasn't supposed to be there. I would be asking the guy that put it there what he is going to do about it. I would also be considering getting rid of the left impulse coupling as well.

Regards

Brent Regan

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