What you have is a flooding situation which can be caused by the following:
Float level might be off. This does not normally cause flooding unless it is off quite a bit. Float can be too heavy, keeping the needle open too long. If you have a brass float then heat up some water and immerse the float. Any leaks can be detected by bubbles. If you have the nitrophyl float, then the only way to tell if it has absorbed any fuel is to weigh it with a gram scale.
Dirt in the needle & seat - This often happens after a new rebuild. Dirt from the gas tank may have re entered the carburetor. Over 50% of carburetor returns are caused by dirt in the carburetor. Fuel pump pressure is too high. This is highly suspect if you recently replaced the fuel pump, or put an electric pump on without a regulator. Check with your motors manual for the correct pressure. Make sure the gasket was used on the seat. Also check it for cracks and make sure the old gasket was removed. Any problem here would allow gas to enter the float bowl bypassing the closed seat.