Leaking fuel - sticking float? - float valve or seat?

[deetrumpet]

My 1982 CB650 is dripping gasoline from the airbox drain line.

1. Can this be caused by anything other than a sticking carburetor float?

2. Is there any way to figure out which of the four floats is sticking without removing the carbs from the bike?

3. Is there any way to smooth out the float valve seat, other than to stick in a Q-tip wetted with Brasso and spin the Q-tip?

4. How long does the rubber tip on the float valve typically last before the valve has to be replaced?

5. Is there anything that can go wrong with the float valve other than the rubber tip?

6. Can anything make a float stick other than its float valve or gasoline that got inside the float pontoon?

Brett Klein, Los Angeles

[Volker_P]

In principle, the floater bowls should have an overflow so that fuel should pour out of the bowls directly and not go into the airbox. There are hoses on the overflow nipples which might be plugged. One may remove them for a test. If still nothing there but in the airbox, one has to check the carb bowl overflow tubes. One may start try blowing them trough from outside. Note that the drain screw at the bottom of the floater bowl uses a different channel, so one should be able to blow through even with that screw installed.
Another option might be fuel dropping from a leaky tank seam on the airbox from outside.