Well it sounds like to me that the needle valve is stuck and not working properly. It may have some residue from sitting on it that makes it stick. The float could cause it but most likely the needle valve and or seat need cleaning. This crap they make called gasoline is junk and causes a white powdery substance to accumulate on internal carb and FI parts. The other thing may be that when the carb was rebuilt that someone forgot to install the needle and seat.. That would also cause it to over flow like that. I hope I was able to help. Henry