Next time you shut it off, let it sit for about five or ten minutes, then pop the hood and remove the air cleaner lid; if you see fuel oozing out of the boosters and the butterflies are wet, it's heat-soaking and boiling the fuel in the float bowl, flooding it. Check the float level at the sight hole and try reducing it.
If you don't see any fuel, pull the linkage and see if you get a shot from the accelerator pump shooters; if not, either the float bowl is boiled dry or there's an internal leak.