Boat Flooding?

I have a 2007 Moomba with the 340hp EFI engine. Last weekend and again this weekend after riding around with no problems and stopping to float the boat after restarting would sputter and die and would not restart. When this happens you can smell gas and I assume that the boat is flooded. Only way to fix problem is to wait about 30min to an hour and boat would start up fine and ran great. It has happened twice in the last two weeks and only happened twice in the two previous years. What is the cause of this problem? Could it be bad gas? Rocking of boat while swimming sloshing gas around? It is very embarrassing when this happens, look for suggestions.