Well Mark its one of a couple of things,it could be the floats in the carb just sticking so will keep filling the carb with fuel till it leaks into the over pipes,or the needle jet that the float pushes up against may be dirty or worn so if the float is pushing it up properly it still wont shut of the fuel,if you have had the carb apart recently you may have knocked the float height out(you can adjust them) so take the carb off and inspect and clean,hope this helps
mikec
September 2010