318 Can't keep fuel in filter, stalls when hot.
I don't know, but why block the vent on the gas tank? Seems it needs all the venting it can get.
I tell you, REAL vapor lock is rare but it sounds like that might be it. I would just try to isolate every stretch of fuel line completely away from any heat source.
Lastly......try some non ethanol fuel and see if that makes a difference. He may have run into some fuel that had a higher content and boils more readily.