f-20 Magneto Troubles

Ryan Lander · Apr 3, 2010

Started my f-20 3 days ago after sitting all winter- Fired right up. Tried to start it today- no go. Took mag apart and cleaned it up, gapped points. Has excellent spark. Put mag back on tractor....it will fire as long as the impulse is clicking, but as soon as it locks up directly the tractor dies. Any ideas ???? Thanks

Ole Shovel · Apr 3, 2010

Check immediately after it dies if you still have spark ? If not suspect the coil. If still has fire the impulse parts, hub pins, trip weights or drive cup may be worn out.
IHC Magneto Service Manual

Ryan Lander · Apr 3, 2010

If you crank it over it will fire again immediatly after it dies. As soon as the impulses stop the engine stops. How could these parts wear out from sitting for 3 days ?

steelfronts · Apr 3, 2010

Ryan change your spark plugs. When the impulse is working the spark may be a little stronger than when it disengages. Another thing is that the timing is suddenly advanced upon disengagement and may put the spark to the plug when there is more resistance due to the increased compression of the air fuel mixture making it harder to jump

Tom Fleming · Apr 3, 2010

This doesn't make sense. The faster you turn a mag, the hotter the spark. That is why there is an impulse so that you can get a hotter spark at hand cranking speeds. the impulse spins the mag faster under spring tension.

I am not challenging your statements, but this really just doesn't add up. If the spark is hot at impulse RPM's, it should stay hot, and get even hotter at higher RPM's, ie. running.

I need to noodle on this a bit. Although it could be the coil has a partial short in it, and it doesn't ground out until you are getting the higher voltage from the higher RPM's. the condenser may be playing a part here to. I have just never heard of this behavior before.

Ole Shovel · Apr 3, 2010

Ryan, The impulse should not be clicking or impulsing all the time even after it"s started and running if so set the idle up faster so it won"t be clicking all the time. Those are metal to metal parts and with it impulsing after it is started or all the time idling is going to wear the impulse out faster and just eventually ruin it. The impulse is just for spinning it over faster for a hotter starting spark after that it should throw out. If not you are just idling it too slow or impulse parts are worn out or got a weak impulse spring. Be sure to run non resistor spark plugs and metallic core wires with a magneto not resistor plugs or carbon core wire. Also make sure hasn"t got moisture in the mag. Mark"s Magneto in CT has a gasket set for the F4, F6 mags now too.

Ryan Lander · Apr 5, 2010

The impuls clicks while cranking as it should..... I never said it kept clicking. I said once the impulse STOPS clicking (which is like 3 or 4 revolutions....) the engine quits.

Ryan Lander · Apr 9, 2010

I was thinking- if the coil was weak, wouldn't it make hotter spark with the impuls (because it's fast) then when it locks up to direct drive couldn't it produce weaker spark since it's not getting that quick snap action ??? It baffles me how it ran beautiful three days before, and then nothing ! I know one thing- I need to rig up a starter- troubleshooting this is tiring me out !!!!

36F30 · Apr 9, 2010

Sounds like you need a condenser to me, and a light spray inside of CRC-556 to dry it out

Ryan Lander · Apr 10, 2010

I'll check that out ! Thanks

f-20 Magneto Troubles

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