how do get an external coil to fire on a magneto for a JD...

gdtractor · Aug 31, 2015

I am trying to see if my coil on my magneto is bad AND if the tractor will FIRE !!!
The engine is loose .. It is not getting spark.. or at least it is not firing with new plugs ..
it has sat for quite a few years in a barn - again .. the engine is free ..
I AM IGNORANT .. on this stuff as USUAL !!! I thought about wiping the points off .. but don't know which "mound" it is on ..
I need to know a lot I KNOW! But would like to know how hookup an external coil AND where and how to get to the points - PLease!
Thanks so much !!
Gary

old · Aug 31, 2015

Depends on the mag you have. If like the Wico on my JD-B you simply unscrew the 4 screw heads that hold the black part on the mag pull it off and there are the point right in plan site. As for doing an external coil that is easy also if your has battery start just by taking the wire off the points that is there now and hook up the non ignition side of the coil to the points

gdtractor · Aug 31, 2015

Thank you so much !! that is exactly what I wanted to know!!
Gary

John T · Aug 31, 2015

Whatever you do, if you have a Magneto DO NOT apply hot battery voltage to its coil or you will fry it.

Often the cause of no fire is the points are badly burned or pitted or carboned up. Its possible to clean/buff/polish the points and it will fire again. If they are bad sometimes they can be filed and make it work but thats like the last report and they really need replaced. When the engine is rotated the points will eventually open up on high cam lobe and their gap should be 0.015 then if its a Wico C or X mag that is. If its a mag it needs to snap/impulse to fire at cranking RPM or theres no starting spark. If youre not familiar with it best have a professional look at it.

Its possible to just use the mag points to make and interrupt a battery powered external coil to make it fire. Ignition switched voltage goes to coils LV primary input while its output wires to points to make and break coil current but theres no RPM based advance like on a distributor, Its NOT any preferred method but yes Billy Bob and Bubba it can "work"

John T

gdtractor · Aug 31, 2015

Thank you !! Gary

RonMC · Aug 31, 2015

If it has been sitting a long time, there is also the distinct possibility that the impulse mechanism has gotten stiff from lack of lubrication. If you are not comfortable removing the mag, you might ask a mechanic to do it for you, and then re-install after you lube the impulse mechanism on the bottom and put it in a vise and turn it (in the proper direction) until it frees up. I have had this problem and it's totally disabling and easy to fix. The real test for this would be to tow it so the mag is spinning faster than the starter can turn it, where impulse is not required. If it starts, do the process above. - RonMC

how do get an external coil to fire on a magneto for a JD...

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