I had a '72 164 that for years appeared to vapor lock when the ambient temp was 80F or over. By chance, I finally found a tiny pinhole in a length of neoprene gasline that acts as a flexible bridge in the steel incoming line. Believe it or not, there was never enough fuel leakage to drip, but sufficient air would get sucked in on warm days to cause vapor lock. If you follow the incoming gasline down along the driver's side of the block, about half way down and a foot or so from the engine front, you should see a steel keeper-loop bolted to the block, through which the neoprene line passes. In my case, the pinhole was on the back side of the gasline, obscured by the keeper, and probably abraded by it, as well as becoming embrittled by heat from the adjacent block. Once I replaced this short length of neoprene, problem was over. You may have other problems, but I'd certainly rule this one out in your troubleshooting. Good luck.