H goes into missing spirts

Having this tractor sitting in front of the barn, I finally drug it into the shop to see what kind of potential this machine has. Its a 46' H with the 152ci., mag, 6-volt system, nothing special was given to me a couple years ago from a lady who wanted her barn yard cleaned up. Need a gas tank & alot of tlc. Didn't run @ the time. So, after getting it in the shop, checked compression on it, all cylinders were @ or near 100psi. Rebuild the carb, mag & so on, to get it running. Now she is all prettied up & working in the field. It's job is to run the 1033 New Holland Stack Wagon during summer & haul firewood in the winter. Very stout tractor, just don't like the big jump from 4th gear to 5th gear.

With my issue. After running it for idk, 10 or 30 minutes, it starts missing on 1 or 2 cylinders. Does that for 5 maybe 10 minutes, then hits on all 4 again. Has done this 3 times to me now. Can't figure out what it might be.

When the mag was off the tractor, point, capacitor, and coil, might have been another thing was replaced. Total inparts for the mag was 125. New wires, plugs. Did not replace the cap or the dust cover. Any thought what it might be?

When it starts missing again, take a screwdriver and tap the side of the carb a few times..I have seen carb floats stick and cause excessive fuel miss..if it quits missing you have a bit more carb work to do. The float has to be set right

Is a 1033 a 69 bale wagon? I think that's like mine, and it is a pretty good load for an M on the road with hills of any kind. My longest haul is about 4 miles, then I give up and haul it on a trailer. I'm surprised the H handles it OK. Especially the tongue load.

Does the tractor ever miss at full throttle or under load? It may be flooding out a couple of spark plugs. A leaner mixture may help, and I suppose you know the mixture screw is an air screw, trun it out for more air and a leaner idle mixture, in for less air and a richer mixture.

Hopefully, you installed non-resistor spark plugs and copper core plug wires, but I really don't think that is the problem here. What I think might be happening is that since the engine has been setting for so long, there is now some rust in those cylinders, and of course there is always a carbon build-up. I think little specks of the rust and carbon are breaking loose and then lodging temporarily in the gap of your spark plugs. With the actual compression as high as it is, those specks are eventually blown out, and then all is well again for at least awhile. The solution might be to get the engine good and warm, and then make it work hard for 30 minutes or so.