has it done it before,if you open your hood does it improve or not, might be a dumb suggestion check you fuel filter 1st and go from there. is it a return or deadhead syst, fuel pressure guage ?
I fooled around one race day with a gallon of methanol trying to mix it with gas to lean it out as it runs rich, never thought you could vapor lock a open engine at night but it did I think it was doing it in the fuel pump, it doesnt quite work like ethanol