just to confirm its a carburation issue, start the bike then switch off the fuel tap, let it run a while to lower the level in the float bowl, then briefly switch it on and back off top top up the fuel in the carb, do this several times... see what effect this has.
As for fuel passing a worn float valve...normally you would see fuel pouring from the carb overflow pipe if it was a bad case.
What about the choke plunger, is the seating good and are you sure it is closing off properly?