135 gas won't run

I have a 135 4 cyl gas that my Dad bought new in Dec. 1965. Dad sold it in 1979 when he retired. I got it back bout 6 years ago. It was sitting in the previous owners barn not running. I winched it on the trailer and hauled it home. It had foil and clothes pins lining the gas line. The owners son told me it vapor locked, so they had to protect the gas line. It was so difficult to keep running they quit using it. Well I could fix it, I thought. It wasn't vapor locking because after I got it running It might run all day without a hiccup or it might not run 5 minutes. There was no pattern to it. I have worked on tractors for a lot of years, but this thing has me flustered. I rebuilt the carb twice, put in new plugs, plug wires, points, condensor, rotor button, dist. cap,
anything else I could think of. I even bought another tractor and switched parts. I tried another carb, and my carb worked good on the other tractor, my tractor wouldn't run with the other carb. I switched everything I could think of. The other tractor ran fine with anything I put on it from my tractor. Nothing from the other tractor helped mine. Carb, fuel line, sediment bowl, distributer, anything. I think it has to be fuel related, because when it starts missing, pulling the choke, will help it run for a while. It will idle, but give it any throttle, it will quit. Any time the governor kicks in it will quit. I even tried a new ignition switch. I tried adjusting the governor. Any Ideas?

I had an Industrial 20 with the 3 cylinder Perkins gas engine. It would run fine and all of a sudden would hardly run at all for no reason...it would keep running only with the choke pulled all the way out and then it was just barely running (you could crawl faster than the tractor was moving). I'm no mechanic but finally, after trying everything, I unscrewed the sediment bowl assembly from the fuel tank...all sorts of junk washed out of the tank...evidentally the stuff was floating around in the gas and periodically a piece would clog the pipe leading to the sediment bowl assembly.
Anyway, I removed and cleaned out the gas tank as best I could and then I made a sump with 3/8" GS pipe with an "el" to the sediment bowl. I capped the sump and would periodically remove the cap and lots of trash would exit the pipe.
This fixed the problem. Finally the sump ran clean and the tractor ran all the time as it was supposed to run.
Hope this helps.

I think you're on the right track with the fuel tank. My 202 had a Por15 treatment before I got it but I don't think it was cleaned out well enough before putting the paint on. I was getting flakes of paint with rust on one side plugging up the fuel filter constantly. I took off the tank, cleaned it out as best I could, beat it up internally with a chain and shook it. Rinsed it out many many times, got it all dried up and said forget about the coating. It worked a bit better but I still had some chunks falling off from time to time. I replaced the fuel filter with a sediment bowl which it should have had in the first place and that made it easier to clean out without replacing filters all the time. Eventually, after many cleanings of the sediment bowl and carb. it finally started running right MOST of the time. If I'd have known all the trouble it would be, I would have bought a new tank and saved myself the trouble. But what you describe is exactly how they run when they are starving for fuel. Because it's ok some of the time I would say it's not the carb but more the fuel supply starting with the tank.
Good luck!!

Edit: Just for curiosity, what does your compression look like?

compression is not great but ok. It is pretty even on all 4 cylinders about 125 I think.