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I acquired a JD model B from a friend when he died and not sure what all he has modded. I used it for a few years in parades and for grading our private road but now it will not stay running. It fires up fine and runs great but then just dies. Seems to have plenty of fuel flow to the carb and the carb looks clean and good. It also fires right back up but still will not stay running. I pulled the mag open and the points, rotor and cap are pretty worn and need replacing. It also seems to be bypassing the mag and using a 12 volt coil and just the points in the mag to fire the coil. Is it possible to update the ignition system to something better? Is this a common issue? It really seems to just completely die like the ignition fails, when I check it I still get spark but then it also always fires right back up. I plan on repairing/replacing the ignition system and plugs but the cap does not seem to be available until at least Sept. and I am not sure why the individual 12 volt automotive coil. I also do not want to spend $$$$ on the model C mag if there is a better solution. HELP.
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I had a JD H with a Wico mag and it would start but had no power and stall, after replacing cap and coil, found the coil spring was broken


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Your problem seems to be consistent with a bad condenser, coil, or loose wiring connection.
Sounds like it was cheaper for your friend to repair the ignition the way he did rather than buying a new mag.
When you replace the parts in your ignition and are waiting on the cap, Clean the contacts on the old one with a pencil eraser.
It's not as abrasive as sandpaper and, cleans electrical contacts to a smooth shine.
Late model B tractors had a battery ignition system on them other than a magneto. I don't know what would be involved in changing one over.
Though one could most likely find the parts from a salvage yard. Maybe new from mother Deere. I'm not sure what they still support.
 

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Discussion Starter #4
Thanks for the replies, I will order the parts and see what happens. I will repost when I have it all complete. The contacts in the cap are almost arched thru, nothing much left to polish. The tractor belonged to a good friend that had it most of it's and his life for all sorts of farm use. He was very proud of it and did everything he could to keep it running. He died of cancer and left it to me, I keep it to honor and remember him.
 

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Just 'refreshed" my 1938 JD unstyled B. Rebuilt it in 2008. Had not started it in 6 years. Stored in barn. Need to sell it, so my son and I pulled gas tank and carb. Cleaned carb, bowl and lines and cleaned and coated the tank. and still couldn't start it, even with non ethanol gas. So broke open the Wico C mag. Replaced condenser and points. You don't have to reset timing if you are careful to gap at .15 on the high spot (see youtube). Cleaned the spark plugs. Got spark, half choke and popping johnny kicked right off! Beautiful Sound.
 
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