Yep, good old vapor lock. Some folks use phenolic spacers between the carb and intake manifold to help reduce some of the heat dissipated to the carb.
One option: 100LL aviation fuel would also prevent your problem but engine would be slightly harder to start. Avgas has a lower and more uniform vapor pressure than automotive gasoline, which keeps it in the liquid state at high-altitude, preventing vapor lock. One plus on aviation fuel is that it doesn't stink like regular gasoline so spills aren't as problematic.
I can't vouch for 100 octane (car) racing fuel. I don't think it would solve your problem because it isn't designed to prevent vaporization at high altitudes.
I had an old ford minivan that vapor locked. I fixed it by wrapping pipe insulation over the gas lines. This actually kept the lines cool by keeping it from the heat. Maybe some type of insulation over the entire carburetor and fuel lines might help. I don't see it hurting anything.
I added that teflon chain lube in the fuel/oil mix during our summer.
Seemed ok, sounded less "metalici". That was 6 or 7 months ago, still going strong. Due for anothr "fix" cos ya only do this on occasions, sort of a "treatment" to line the cylinder with something on a HT btw.
How much did I add ? ( I am not a purist)
Well, there was about half a bootle left so I added the lot in half a tank of fuel.
Large is correct in saying you can insulate the fuel line to keep direct heat away. Some cars have the same prob. when a carby is situated above the exhaust manifold or the fuel line runs close the some part of the exhaust.
Come on down to balmy Tucson, it's only 107 here! My R/S does stall out at idle occasionally, but it's not a big deal. Tried fiddling with the idle screw, won't do that again. That thing is touchy! (the manual advises against messing with it, and they're right)