Farmall Cub

Tim Heitman

New User
should a cub with magneto be negative or positive ground I am trying to get a barn find tractor going cant get any fire from mag, cleaned points up good but still no fire what should I try next
 
The magneto should be independent of the electrical system + or - shouldn't matter. Is the impulse working? I only have a couple of engines
with mags on them, never had a problem with either, so I don't know much about them.
 
(quoted from post at 07:15:39 11/18/17) The magneto should be independent of the electrical system + or - shouldn't matter. Is the impulse working? I only have a couple of engines
with mags on them, never had a problem with either, so I don't know much about them.
ow do I tell if the impulse is working
 
When your tractor left the factory, it had a "positive" ground. You can easily check the Mag by pulling a plug wire and holding it about 1/4 inch from the frame. If your find was any thing like mine, you my need to do a complete rewiring job. Very easy to do. I use either "Autolite" or "nsk" plugs. Old age and mice work wonders of the wiring. One improvement was I added a "Zenith replacement Carb" from this site. Made all the diference in the world.
 
The battery is positive ground. The magneto has nothing to do
with the battery. J4 magnetos in my experience often have bad
coils.
 
(quoted from post at 08:44:07 11/18/17) The battery is positive ground. The magneto has nothing to do
with the battery. J4 magnetos in my experience often have bad
coils.
How do u check to see if coil is bad
 
As it is cranking the mag will make a snapping sound as the engine turns. It is medium loud and may need you to be near it to
hear it. If no snap, no start. If you pull the tractor about 4 mph in high gear it will start with a failed impulse. If it
clicks, it could be the points. They are not complex, but a book or Youtube is a good idea. Jim
 
I have a coil & condenser tester & work on mags as a hobby. (cheap) Let me know if you need help. Maybe the mag was bad when it was parked??
 

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