electric fuel pump? maybe the oil pressured controlled switch is thermally intermittent?
Could be "vapor lock", especially given today's "fuels"....Take some IR gun readings next time it hot soaks. Most OEMs, when they spec it, don't want any temps above 150 at the carb's flame arrester level, and ~ 110 (def F) anywhere on the fuel path.
Two things that may help: 1) run the engine at fast idle a few minutes and then shut it off, & 2) when doing the warm start, slowly advance the throttle to at least half way and then crank it over. As soon as the engine starts, pull the throttle back to ~ 1500 and once the rpm stabilizes, normal idle.