Rebuilding F20 magneto

VER · Aug 26, 2010

Bought a magneto off an old F20... trying to get her sparking again. Took points out and polished them up, put them back and set it to 0.013". Put voltmeter on spring that connects out to the distributor cap and the needle of the voltmeter moved ever so slightly (it was set on 10V). Tried seeing if there was any juice going to the condenser and again it barely moved. Then checked it to the points - again barely anything.

Anyone have any ideas what I should look at next? I"m no pro at these - never done anything but replace points, so any help would be greatly appreciated!

Thanks!

Ohiohillbilly · Aug 26, 2010

Which mag do you have?? How fast were you spinning it?? Need more info.

F-Dean · Aug 26, 2010

Try replacing the coil. YT (This site) has them.
I put a new coil and condensor in a F-20 mag (Model F-4) and got a 3/8 inch spark.

I used a method described here several years ago.
Find a 3/8 inch drive socket that fits the nut on the "Front" end of the armiture. Cut a 3/8 inch drive socket extension in half. Put the male end in a drill and use that and the socket to turn the armiture. Hold one of your spark plug wires near the base as you spin it. Move the spark plug wire away from the base as you spin it and see how wide a gap it will jump. As I said above, I got mine to jump 3/8 of an inch.

One thing extra that I did was to drill a small hole in the inside of the mag cover, connected a wire to the condensor, threaded this wire through the small hole and connected it to a one-wire "Kill" switch from a H or M. This makes it much easier to kill the engine, especially if the original grounding mechanism does not function.

El Toro · Aug 27, 2010

Check the magnets for magnetism. If they're weak
you won't get any fire or very weak fire. Touch them with a screwdriver and see if they attract that screwdriver with a lot of effort. Make sure your impulse coupling is snapping. Hal

VER · Aug 27, 2010

It's an F4 mag. I wasn't spinning it fast, just 'snapping' it around with my hand.

Even if the coil and condenser were shot, wouldn't I still see a big jump in voltage at my points when it snaps?

teddy52food · Aug 27, 2010

The F4 uses a big horseshoe magnet on the outside. Get it charged up again, get the coil and condenser tested & with good points it will make a good spark, if the impulse is snapping as it should. I have never tested the voltages in a mag but I think it will be small on the primary.

Janicholson · Aug 28, 2010

With an oscilloscope wou could see it. volt meters do not read impulse spikes well at all. The others have your answers. Jim

Rebuilding F20 magneto

VER

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Ohiohillbilly

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F-Dean

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El Toro

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VER

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teddy52food

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Janicholson

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