Tab, you may the exception... VAPOR LOCK HAS HAPPENED!! When these old trucks were in 100 degree plus temperatures, the engine was a lot hotter and the fuel line was no more than 1 inch from the engine, thus causing vapor lock. Have you ever driven a 216 or 235 engine in 100 plus temperatures for eight plus hours a day? I have, when I was a young teenager on a farm... and they do VAPOR LOCK! Now, I am not saying this is the problem here, Phillip doesn't have the same conditions, a stuck heat riser could cause this also.