" When you can't fix the carb no matter what you do maybe it's not the carb!"
That's why I have enjoyed servicing carburetors:
I always suspect the manifold first.
(And Pans have been found to leak even at the valvecover screws over the intake ports!)
Back to the heat issue:
Cold motors require a much richer mixture when cold than warm. That's why chokes were invented.
If a hot motor is hard to start for no other reason than carburetion, then it should be suspected to be too rich. This can occur because the machine is tuned to maximize cold starts, without fully dialing in the high speed mixture. The Panhead carburetor's circuits will affect each other, and trimming to find a medium between the two takes alternating trials. (Referring to real Pan carbs, of course!)
Ideally, settings can be found that offer easy starting as well as highway performance.
However, the transition from low to highspeed circuits can be complicated by borewear from the throttledisc. When the eyebrow groove of wear into the carb casting extends as far as the idle bleeds, then idle and lowspeeds must operate under conditions that are no longer intimately controlled by the disc. So optimizing the low may conflict rather than compliment the high, especially if you are trying to fatten it up to cure the "flat spot" so often associated with excessive bore wear, loose venturies, etc.
Meanwhile, like Chris,
I think Harley gasline vaporlock is a myth.
(I truly vapor-locked a machine once, but it was a '62 Ford and it was the motor that stuck until it cooled down. Pressure within the cylinders wouldn't let the intake valves open.)
Just my opinions, for what they are worth.