Check the condition of your fuel lines. The outside may look ok, but the inside may be rotting. Mine did what your cart is doing and I kept cleaning the carb only to find tiny black specks in the bowl. Turns out the inside of my fuel line was kinda crusty.
If that is not the problem, I would look at the float and needle valve. Thats where your problem is. Something is keeping the float or needle valve from shutting off the fuel when the bowl is full. Could be a speck of dirt, the spring on the needle is not on correctly, dirt in the needle seat, or a small nick in the needle itself.
Check that stuff out and keep us posted...
