I have been dealing with the same issue with three carburetors, Starts right on cold engine, and after it sets for a hour, its the 15 minutes stops that it won't start. I have tried lowering the floats, but that leans it out where it duns like crap, I have a regulator set to 2 psi fuel pressure, and tried the isolators under each one. Nothing really helps much other then setting them lean. I learn to live with it. Not hitting the throttle helps, but its not the cure. Once started it runs great so I don't worry about it.
Good luck with yours, Joe.
