I had an old bike one time that the float had gunked up where the pin goes into it and had made a microscopic burr in the plastic and the pin was jamming the float up, so i put it on the drill press and ran a bit down through to clean that hole back out (not make it bigger just clean it up) and it operated 100% better on the pin and stopped jamming up the needle.....
Just a suggestion to look at, please dont drill out your float or anything crazy like that, just making a last resort suggestion of possibilities.....
Also take the float out and see if it still floats in water, i know its silly but if they get little pin holes in the plastic they will take on water and not float properly anymore, not allowing the needle to close all the way in the seat.... Also take a float gauge and measure your float height.... And check all around real good on your carb boot and headpipe and all around there for any air leaks as well......
WD-40 will show you any air leaks, check it with the bike running, and spray it all around, if the idle changes at all while your spraying it then you have an air leak causing the gas to overflow, i have seen carb boots go bad many times and cause gas leaks from having an air leak....
Good luck! I:I I know its frustrating but by the time its over, youll be carb expert if you pay attention and learn from these things!