You need to install the correct floats... and probably install jet extensions on the secondaries.
Years ago I had the same issue. One day I just happened to be at GW picking up some parts and remembered that Brad Urbans "Carb Shop" was about 100 yards away. I walked over, talked to Brad, told him my issues and he sent me out the door with a set of road race floats.
http://www.customcarbs.com/carbshopcatalog.htm
I never had any issues with the carb after that.