I have the same problem. After two days you have to crank it a while. I tested it with methanol free gas (kind you used to buy years back) and still have the problem. I even set two spare carbs up on the work bench and filled them with gas, checked three days later and still had gas in the bowls.
I suspect it's draining back to the pump. Putting on a new pump today and will see if that cures the problem.