Farmall H won't lean out

I am starting to wonder if a different main jet or whole carb was used on the distilite models? Could this be my problem.

Also this tractor has a mag on it. Could the mag be weak and not burnig the carbon off the plugs.

Please try to help me out replacing/cleaning spark plugs every 20 hours or so is getting expensinve.

Suggest you tear down the carburetor and give it a thorough cleaning. Pay particular attention to the idle passages and ports in the throttle body casting – that’s where the problem will be. Once the carb’s back on the tractor adjust the idle mixture first for a good idle, then set the high speed screw so you get a clear exhaust at governed RPM.

Unlikely your problem is magneto/plug related. It’s the heat of complete combustion – not the spark – that prevents carbon from building up on the plugs. Your carburetor is running rich. The resulting incomplete and relatively cool combustion is causing soot (carbon) to accumulate on the plugs and fouling them out.

Not familiar with the H but all carbs I have ever seen have separate adj for load and idle. One does not affect the other.

Distillate engines have lower compression heads so it is probably running cold with gasoline. The hotter plugs should help and maybe advancing the timing would help. Gas burns slower than distillate (A very low octane fuel called "tractor fuel" but no longer available) so it needs more advanced timing.