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Magneto no spark

D

Dan W MN

Member
Hi all

I have a 48 M with no spark from the magneto. After disconnecting the ground(kill) wire, I found that I have continuity between the ground stud and the tractor frame. Seems to me this should not be the case, though i have no experience with mags. can anyone point me towards a good magneto troubleshooting page, or offer any advice?

Thanks
 
are the points in the mag open when you test??? there should be some continuity when theyre closed...check gap on points and make sure contacts are clean...condensors go bad too ...mags are just like a conventional ignition with a built in generator.
 
The points are usually closed except when firing so that kill stud should have very low ohms continuity to frame via the closed points. When you use it as to kill the ignition it does so cuz then the points are ALWAYS effectively closed. If you put an ohm meter on that kill stud to frame it should read like 1/2 to 1 ohm or so when points are open (coils LV primary resistance) but near 0 when closed. Points oxidized or burned or pitted or carboned are the usual cause of a mag spark problem next would be a bad condensor.

John T
 
Clean the points until they're shiny, then see if the tractor will start. Hal
PS: If they're pitted replace them.
 
On a Magneto,the kill wire terminal is also the insulated terminal of the points. This is also the point where the coils primary wire is connected. The difference in the resistance reading between the point being closed and open, where you read the resistance on the mag coils primary is most of the time around ONE OHM of less. Most ohm meters, especially digital's, can not tell the difference of one ohm and zero ohms. I have a few ohm meters. I recently bought a relatively cheap analog meter from MCM Electronic just for the shop. If it got damaged it would be no great loss. TO MY surprise, I found with it set in the RX1 range I could read the difference between open and closed points in a Magneto. It was a VERY pleasant surprise.

Kent
 
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