Hello Jeffbob, welcome to the forum.

According to my favorite Ford tractor guru, UltradogMN.... "Always, always check your spark first. If you are satisfied you have good spark at each plug then go on to fuel."

Confirm that you have a strong bluish-white spark when engine is cool and running well. Check again when the engine is warmed up and running poorly. An orangish spark is not good enough. Coils sometimes are temperature sensitive. If the spark checks out OK, both cold and warmed up, go to the fuel supply.
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Have you tried choking (various choke positions) the engine when it runs rough? Does it improve with the choke?

Pull the plug in the bottom of the carb and catch gas in a clean pint jar. The jar should be filled in 2-3 minutes. If not, then you have a fuel delivery problem.

Your tractor has a number of fuel screens: 1) There is a cylindrical-shaped fuel screen attached to the fuel tank shutoff valve, sits up inside the tank. 2) If your tractor has a fuel pump, the is a screen at the inlet to the pump. 3) If your tractor has a sediment bowl, there is a screen up inside at the top of the bowl. 4) There is also a screen in the elbow at the inlet to the carburetor. Check the fuel screens and clean as necessary.

 

Sounds to me like a vacuum leak. Think I'd renew all the vacuum lines before doing anything else.

 

Could also be an intake manifold gasket leak when the engine warms up? When it's running poorly, spray a little WD-40 or starting fluid (ether) around the intake manifold and carburetor seals and see if your RPMs change.

 

Thanks for the ideas everyone. I will let you know what I find out.

 

Problem seems to be a bad plug wire. I changed the wire and it's running fine now.