Vapor lock on '75 1.8? Options

[57lincolnman]

I was driving my '75 1.8L on a very hot afternoon (+94 degrees) in combination highway and city driving for about an hour. While waiting at a stoplight, the idle became very weak. I gave it some gas, it backfired (twice) and then died. I got it to fire-up again but the car barely had any power - just enough to barely get through the intersection. Then it died completely. After sitting for a few hours, it started right up again. Prior to that the engine would hesitate when getting out of first and then go.

I was at PCA event today and some 914 gurus suggested it could be vapor lock. Is this rare in 914s with the fuel up front? Is it still possible even with the engine running to get vapor lock? Or could this be a fuel pump starting to fail, or perhaps a relay? I have stock L-jet fuel injection. Up until now the car has been running very well. Checked for vacuum leaks and found none. Fuel lines replaced a few years ago with stainless steel. Thanks for insight.