I don't see how an "Air Gap" manifold could possibly be heating up the carb to the boiling point. I mean, look at the pic of this manifold:
There's just no way for the heat to conduct all the way to the carb, especially not with the engine operating at only 180 degrees.
I'm kinda thinkin' maybe you got a fuel line with too much pressure, either from fuel pump or maybe the line is getting hot. Do you have a portion of the fuel line that is close to the exhaust?? That would certainly cause fuel pressure to build above 6psi.
If possible, drive car around (stay close to your garage) until the problem starts, then as soon as you start noticing the problem, get vehicle into garage, disconnect fuel line (careful of excess fuel spray) and hook the line onto a fuel pump pressure gauge. Then start car and let run for a few seconds from fuel left in bowls and see what the gauge reads.
Also, when you disconnect the fuel line, if there's a lot of excess high-pressure fuel spraying out, then that's a good clue the fuel pressure is too high. Keep fire extinguisher handy. Gas spraying on hot engine is never a good thing!
The problem really sounds heat-related, otherwise it would be flooding out at all times.......................