John Deere A Still won't run. Here's what happened.

A problem only after a warm up in a mag (or even a disttributor) can be due to a bad condensor or coil. Its my guess the rebuild probaly replaced the condensor but not the coil do you know????? ????? ??? If the points and condensor were replaced at rebuild and she bench tested cold but wasnt run a long time, a warm coil problem wouldnt have shown up. If you check for any shorted kill switch or kill switch post or wire problems as clooney mentioned, and she still shows no spark as you said after she dies, and the points are gapped 0.015 to 0.017, due to the low cost, I would first simply try a new condensor. If she still dies ONLY after warmed up and you rule out a carb problem, I would then wonder about the coil. A coil can bench test cold fine but develoo a problem after warmed up.

Inspect the condensor and points and any kill switch wires or post and the gap and if she still starts and runs fine but dies only after warmed up and its NOT a carb problem, I suspect the condensor first then the coil.

Let us all know Merle, this is a tricky one lol. Good luck n God Bless Ol John T Nordhoff in Indiana

Just suggesting another possible avenue to explore.

~If you are losing spark when it quits you have an ignition problem. Are you sure it's a Wico X mag & not a Wico XH distributor? They look almost the same. Does the mag snap when the engine is turned over slowly? If not maybe it's a distributor. The Wico distributor will have a little oblong cover on the front with a wire stud in the cover..

~If it is in fact a Wico X mag, start by making sure there is no external wire attached to it [if there is, REMOVE IT],,,if it had a wire & removing it doesn't change your problem you will need to try a few things.... Try a new condenser [if the condenser is shorting to ground or going open after a little use it will shut the mag down],,,make sure the points are set to .015",,,make sure all the internal wire connections are tight & not corroded,,,if it still acts up, try a new coil [maybe it is going open hot]...Are the plug wires solid metal core & not automotive TVRS [carbon core]? If not change them...

~If you can't find anything wrong with the mag you might have to swap a mag from another tractor just to see if it really is a mag problem. If a different mag eliminates the problem you know for sure you have a mag problem, if it doesn't you have other problems like fuel/carb..

~If you can't borrow a mag for a test you can take an old plug wire & cut it about 4" from the spark plug end, then strip back the outer insulation for about 1/4" on each piece to expose the inner metal wire, then find a 1-1/2" to 2" long piece of clear plastic hose that will just push over the plug wire ends, then push both the cut plug wire ends into the tubing until the wire ends are about 1/8" to 3/16" apart. You can then install that wire on the tractor & watch the spark in action with the engine running [will need a dark place to do this in]. With that wire you will be able to see if the spark quits first or the engine quits before the spark does...