if you had a new carb then that one isnt right either!the system works as follows,
the fuel tap opens when a vaccum is drawn on the air pipe witht he bike running,the fuel flows in the carb via a brass pipe that leads to the float needle seat the float has a needle on it the is joined to a float when the fuel goes in it runs past the float needle through the float needle seat and fills the float bowl up ...the float rises like a bouy and the needle is loosely fixed to it so as the floats rises it pushes the float needle into the seat and stops the fuel from coming in.so if its still leaking then the needle is either stcuk of has a bad sealing end the seat could be worn or the float may not be bouyant i.e have a split in it or crack so its full of fuel and not floating .its very simple these have a plasti float so it cannot be adjusted like a metal float can .
adam bike doctor, January 2010