Posted by smiley458 on August 22, 2012 at 17:51:01 from (4.157.8.253):
The impulse coupler gave up on an FMJ mag on my rarely used Allis Chalmers B, so I converted it to battery/coil ignition. I have a great deal of experience with battery ignition but not much on mags. I disconnected the mag coil wire and removed the coil to cap rod, drilled the cap to accept the coil wire, wired a switch to the coil and hooked the negative side of the coil to the grounding lug on the side of the mag to the points, timed it to the required 30 degrees advance, have 1/2 inch blue spark, cranked it over and it immediately fires up runs a couple seconds, then immediately shuts off. I've been pulling my hair off and on about this for a week, tried 2 different (bad)mags with the same results. My understanding of the mag is that the impulse coupler retards the spark for starting while also spinning it much faster to generate more spark. Have also searched the net to see if these mags have some type of built in advance that would advance the spark way to far and prevent firing as rpm's rise. It seems that if that was the case, it would knock, try to kickback and backfire, but it shuts off as if the switch was turned off. It will immediately fire up and quit again. I could yank and install this mag in my sleep now and it's got me stymied. Any thoughts will be appreciated.
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