About three years ago, I had a carburetor problem with a Miller Big 40 welder. The engine is a Continental 4 cylinder flat head.
The float swelled up and wouldn't turn the fuel flow off. I checked all over the civilized world for a replacement float, but couldn't find one anywhere. The problem with finding a float was that the engine used a Walbro carburetor and it was long discontinued The float is a brown phenolic or micarta-like substance, not a brass float. I assume the new fuel (10% ethanol) was the fly in the ointment.
With nothing to lose by trying to remedy the problem in an unorthodox manner, I decided to sand the float down until it would move freely in the bowl. I compared notes with James Reeve, a friend who has been fooling around with engines forever and he said that he used to modify the float configuration on his race cars and then seal the float with epoxy.
I did this and it worked for a few months, but again swelled up. I again disassembled the carb and sanded the float as I had done previously. There was a tiny hole in the epoxy when I took the carb apart that had allowed gas to permeate the float again.
The second time I let the float "air dry" a day or two before applying the epoxy and it's still working fine. I think the problem was caused by the float out-gassing when I originally coated it with epoxy, causing it to have the tiny hole in the epoxy and allowing it to swell again.
Keep in mind that when you sand the float it needs to have enough clearance to still work when the epoxy is added.