Well something is amiss. The intake on my flathead six literally sits atop the exhaust manifold and I don't have these issues, pretty much as the factory delivered it, no heat sleeves, no heat shields, no return line, etc. Been 100+ for days on end here too.
I would closely inspect the fuel line and make sure it is getting no where close to the headers. Maybe fill up at a different gas station to see if it's fuel related. Get an IR gun and next time it happens get some temps from the carb, fuel pump,, fuel filter, etc to see where the problem is.
I agree. My 528 Hemi in my Charger, a/c, mechanical pump, no return line, premium fuel, no problems even idling in town. I suspect the poster has a fuel delivery problem and not vapor lock. As said check the fuel pressures.
