Farmall F-20 runs rough

Dan Agius · Feb 22, 2010

Can anyone help?
I have a 1938 Farmall F-20. Engine & carb has been rebuilt. Starts well, but runs real rough. I've taken it twice to a local farm repair guy who's tried everything he can think of but can't fix this. Gas tank been cleaned, new fuel filter in line, new spark plugs, carb been taken apart and recleaned, valves adjusted, timing reset. Any suggestions would be GREATLY appreciated!

Brian Love · Feb 22, 2010

do the 2 primer cups above valve cover close and seal good they'll suck air in

lee oh · Feb 22, 2010

does the magneto have a new or newer coil ive had this problem more than a few times

Anonymous-0 · Feb 22, 2010

per my dad, he would have been 88 this year, to make a regular or f 20 idle right you have to set the plugs at about .030 not what the book calls for. this is partly due to better fuel we have now. at the time these were built gas was about 70 octane, also these engines burned distalate or kerosene and were very low compression. doesn't cost much to try this might solve your problem. post back if it does so we can all learn. leroy

Tom Fleming · Feb 23, 2010

I agree on checking the primer cups. You didn't indicate if anything had been done to the magneto. There are a number of things with the mag that could be wrong.

One time I bought a mag that was supposed to have been completely rebuilt and tested. New coil, new carbon brushes, new points, new condenser, and new cap. All of that didn't matter because the person who rebuilt it had the internal timing off inside the mag by 4 teeth. Tractor would start, then if you advanced the timing, it would snort, cough, and quit. I put a different, known working mag on and it ran like a champ. took me 2 weeks until I took the mag apart and found the timing off.

If the engine has been rebuilt, are you also sure that the cam is timed properly? The crank, cam, and mag drive have to be "dead on", or you have a problem. 1 tooth is all it takes.

Something to think about.............

Nebraska Cowman · Feb 23, 2010

Does it smooth out under load? It is a common ailment for F20s to want to buck and gallop at idle. I blame it on the spark jumping around on an uneven rotor disc. You want to take the disc out and sand it smooth. The brass contact plate is pretty thick and you can remove a lot of material. The fiber disc itself will have a ring worn in it from the brushes and you need that ring to disapear.

Anonymous-0 · Feb 23, 2010

You may have spark issues, but have the valves been ground, or replaced as necessary? I set the valves on my 20's at .018.

Longknife · Feb 23, 2010

Compression test????

Farmall F-20 runs rough

Dan Agius

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Brian Love

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lee oh

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Anonymous-0

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Tom Fleming

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Nebraska Cowman

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Anonymous-0

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Longknife

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