Farmall H stops when hot??

We've got a late 40's Farmall H. 12V system. The tractor starts & runs fine for about 10 minutes, than dies. Wait about an hour & it'll start right back up. It's got new points & condenser. This tractor was comverted to a key switch starter, could that switch cause a problem when the tractor warms up?? Fuel flow is good (all new fuel lines & cleaned sediment bowl). Anything else I'm over-looking?? Thanks.

I would check out the 12 volt conversion and be sure it is correct. Sounds like the coil may be heating up and opening when it gets hot, or could be a faulty condenser.

I'd still suspect fuel. Did you open the drain plug on the carb and see how fast it comes out?

Also did it do this before the new condensor was put it? New doesn't necessarily mean good, especially now days when most are made in China.

Be sure you have a coil with a built-in ballast resistor or that there is a ballast resistor wired in line to the coil. A new ballasted coil at NAPA is around 20 bucks.

If resistor is going bad, what happens? Does it open when hot? What happens if I eliminate it (jump it out)? ...Will tractor restart? I just want to know what I need to buy before just spending money & hoping for the best. Thanks

When it quits running pull the coil wire from the cap and hold it near a good ground while someone makes an attempt to start the engine. You need to do this ASAP when it quits before anything has a chance to cool. If you have a hot blue fire from the coil wire your ignition is ok. If this looks ok pull the gas line at the carburetor and remove the tube fitting where your gas line connects and look for a screen that may be plugged. Hal

They're not that expensive. Hal

The ballast resistor can open as it warms up. Jumping around it for a minute to see if it starts back up is not a problem, it just burns up the points and will heat the coil. A volt meter on the coil side of the resistor will tell you if there is an open in the resistor when it quits. With no volts there will be no spark. JimN

This is all assuming you have a battery ignition and not a magneto.

The battery igntion, even on a 12v tractor, operates on 6v. So you will have one of two setups.

A) a resistor inline between your ignition switch and the coil. This reduces the input to the coil, which is wound internally to make your spark from a 6v input. In this case, a failure of the resistor will leave you with no input to the coil. Generally, in my experience with ballast resistors, it just fails, and stays failed. A bad coil often, but not always, will fail as it heats up, when a weak spot in the windings heats up and breaks continuity in the windings, breaking the circuit/field. In those cases, it will often close back up when it cools and run again until its heated back up. If you wire around the resistor, you'll be delivering a straight 12v to a 6v coil. It will take it, but it's hard in the long run on points and condensor. Okay for test purposes, but not general running.

B) In the absence of a resistor, you likely have the other type coil, which is made for a direct 12v input. It doesn't actually have a resistor built into it -- it is wound differently inside from the 6v variety, to produce the same spark.

If the tractor is showing the symptom of dying after ten minutes or so, but restarting and running fine after an hour or two to cool down, before dying again, I'm suspecting the coil. Someone else made the very good suggestion of checking for a spark from either the ignition wire from teh coil or one of the spark plugs ASAP when it shuts down. If no spark then, but an hour or two later, you can figure coil (especially if it is WICKED hot to the touch or seems to have been leaking oil or other stuff). If no spark later either, the condensor and coil could both be suspect.

As far as replacement coils, you have your choice. If you have a resistor, you can leave it in place and buy a 6v coil. You could also eliminate the resistor and buy a coil that takes a 12v input. If you have a 12v input type coil already, just replace it -- I don't see much point in adding a resistor and switching back to a 6v coil in that case.

Let us know how you make out!

27* down here in Waldo County today.

....it was the resistor, jumped it out, it started right back up...I'll buy a new one Tues...Thanks!