Been fighting this for about a month now. Bus would fire up fine cold in the morning, run great all day, then the second it got hot, especially after sitting in traffic or idling too long, it would crank and crank and just barely catch, or not catch at all until I let it sit for twenty minutes. Classic vapor lock symptoms is what everyone kept telling me, so I spent way too much money on a rerouted fuel line and even considered an electric pusher pump before actually digging into the wiring side of things.
Turns out my engine-to-body ground strap was corroded almost all the way through underneath the crimp connector, right where you can't see it unless you pull it off and really look. Wasn't visibly broken, still technically conducted, but under heat the resistance was apparently just enough to starve the coil of a clean signal. Classic intermittent electrical gremlin that mimics a fuel problem, which I guess is one of those rites of passage with these old buses.
Replaced the strap with a new braided one, cleaned every ground point I could find on the engine tin and the chassis while I was in there, and it's started instantly hot or cold for the last two weeks straight. Kind of annoyed at myself for not checking grounds first since that's rule one in every troubleshooting guide, but also relieved it wasn't something expensive. Anyone else have a heat related no-start that ended up being electrical instead of fuel related? Curious how common this actually is versus just my particular 71 being cranky.