318 timing

OK, sounds like it is flooded and your holding the throttle open eventually pulls the excess gas out of the engine.

Next time after stopping with the engine good & hot, wait 5 minutes and the start looking down the carb throat every 1-2 minutes. Put the air cleaner back on between looks. You will probably see fuel leaking down into the carb at some point.... if so, it's boiling out with the heat soaking into the carb.