Take your carberutor bowl off and clean your bowl,float and needle with carberutor cleaner and see if it helps,but like TQuentin1 said you will have to rebuild the carb,especially if it's the original one to the bike.
Take your carberutor bowl off and clean your bowl,float and needle with carberutor cleaner,then turn your petcock make sure the gas is flowing then push-up on the float and see if the needle stops the flow of gas, hopefully it is just gummed up, but, like TQuentin1 said a rebuild might be added to the list. I hope this helps you for now.