Farmall Cub

Do they go bad slow ar when there bad there bad? it will run for a short time the stop running untill it cools off, coil gets warm too a new coil from napa

Interesting....I have one on my 57 and have had problems with the tractor quitting when it runs for an hour or two....I really don't know if they go bad all at once or not but I'll definitely research it and watch you post for replies....I didn't think of the resistor...Dave

The ballast resister is simply a wound wire element, much like a heating element. The typical failure mode is for the element to burn in two. When that happens, they're bad forever. You can easily check it with an ohm meter.

That is exactly how my boat acted when it had the wrong, NO RESISTOR coil on it and it should have. The boat would start and run perfect, but once the coil got hot, it would start backfiring and missing and eventually die. Once we replaced the coil with the correct one with an internal resistor, it ran perfect.

I'm wondering if the same thing is happening here. The resistor is shot, and now the coil is just failing due to over voltage, heating up and breaking down the oil, so you get no spark. Once it cools, it works fine, until the coil overheats again. All along, the resistor is shot, all the time, but the failure youre experiencing is when the coil gets too hot. If it were me, I think I'd get a new coil with the internal resistor, and do away with the old ceramic one. Just my thoughts.

Bill

Would the tractor run if the resister was burnt up? Would't you have a "open" spot in the electrical system? Dale.

Claycomb wrote:Would the tractor run if the resister was burnt up? Wouldn't you have a "open" spot in the electrical system? Dale.

Correct. When the resistor wire breaks, causes an open.

IIRC when resistors get hot their resistance values increase... That could cause the voltage to the coil to drop below a value where it will spark.

When I replace coils I go straight to a native 12V coil and eliminate the resistor.

I swapped coils from another tractor that doesnt need a resistor and it does the same thing. It has an inline fuel filter, I have heard that gravity feed fuel systems dosnt like them, mabe ill remove it to see if that helps

If you've got a sediment bowl you don't really need a filter. It's just filtering twice. My 2 cents, Dale.

Describe the problem in it's entirety.

What diagnostic testing have you conducted?

Have you conducted a complete tune up, including compression tests and valve tappet adjustment?

The wire wound ceramic resister does change resistance as it warms, but it happens in the first second or so, after that it is stable unless it opens due to the internal wire breaking.

John:

I would lose the in-line filter no matter what the problem turns out to be. In-line filters on a gravity feed are problematic if they are not designed specifically for a gravity system. With the Fuel Sediment Bowl and the Carb Inlet Screen there should be enough filtering to prevent gunk from getting into the jet. If you want more protection then look at this thread : How To Upgrade A Cub Fuel System.

I removed the filter and it ran for over 3 hours without a miss.


Thanks

John:

Glad you got the issue resolved and enjoyed your seat time