Agree with Vector1 that vapor lock is the most likely cause. Is fuel boiling in bowls after you stop and let it sit for awhile? To address this problem, get some reflective insulation from McMaster-Carr and insulate all fuel lines in engine bay. Make sure none are touching a heat source, like an
oil line. Then insert a phenolic spacer between the carb and intake, and maybe an aluminum heat shield too, all with extra gaskets. For me, the spacer and insulation fixed the problem with summer gas, but with crappier winter gas I needed to add an aluminum shield for radiated heat.