f 12 Farmall

I have a 1934 F 12 that I brought back to life. It runs really well and crank starts very easily when it is cold. Let it run 20 minutes, shut it off, then nothing.

I have put in a new condenser and coil and it still acts the same way.

My friend has a book on magneto rebuilding. It says that the resistance on the coil should be close to 6000 ohms. The old coil and new coil both measure very close to 12000 ohms. We used two different ohm meters and they read the same.

The old coil was stamped 1/90 and the new one looks exactly like it. The part number is eb108.

If any of you guys have any suggestions, I would like to hear them.

Thanks

After it is warmed up, does it still have spark? Also, what type of wires are you using. Are they copper core wires, or are they composite, graphite?

You may not have an electrical problem, could be fuel. Did you work on the carb? The possibility exists that the float might be rubbing on the side of the bowl of the carburetor. When the engine is cold, metal shrinks. After 20 minutes, the carburetor has warmed up and the metal swells which could cause the float to rub on the inside of the chamber. Another thing to check is the filter screen in the input line to the carburetor. And lastly, is your fuel tank clean?

Checking for spark is the first step. Had a Farmall cub that did the same thing turned out to be the coil. Got another from Napa and it done the same thing and I've learned from past that all new parts have a chance of being no good out of the box and that was the case. Same thing had happen to me before with a portable industrial screw air compressor with a Hercules engine. Took a day and a half to figure it out, got a new coil that turned out the same finally got it narrowed down to trying other things. Took one off a super M and it ran just fine, then put the new one on the super M and it died after about 20 minutes.

Bumblebee,Thats the nature of the beast,The carb are very touchy,I think the gas evaporates out and or runs down in the motor causing flooding.A good fuel pump and correct timing is critical.PLus learning how to start it hot is a issue.All F-Series tractors start different

jimmy

First as others say check for spark at the plugs when you encounter the no start situation. You can blame the magneto all day long but if it is producing a spark the problem is most likely fuel or in this case fuel/air(f/a) mixture. So I second what James is saying older down draft (overhead) carb engines can be very finicky about restart after a short period of hot soak. This is where it gets a little tricky about not insulting someone not knowing their mechanical experience. If you hit the choke any at all and the f/a is already rich you have just ruined your chance of a restart. So try 1/2 to 3/4 throttle when trying to start hot to insure the throttle plate is open for more air. If you encounter this problem try pull starting it with another tractor. If when it lights off a bunch of black smoke belches out you know over rich f/a is your problem. As another poster pointed out maybe there is a carb problem causing a rich hot soak issue. I've never started or even driven an f12, but I do know that figuring out the proper method to start it can also be the answer. Hope this is not a bunch of ramblings and helps you figure out your problem.