mac
i had this problem last year.  i think if you look in the bentley at the
gas tank you'll see some venting tubes above the tank with two "Y" pieces
fitting in the top of the tank.  i think these break all the time.  mine
did and i assume yours are too.  it easy to fix, it took me an hour or
two and i'm not too adept.  you should be able to reach the pieces
without dropping the tank. i dropped my spare tire and took out the tray
that holds it.  i'm not sure this was necessary, but it wasn't hard.
then i reached in and felt the "Y" pieces. they felt fine but one was
cracked to all hell.  so i undid all the hoses connecting these guys and
yanked the offending piece out, which was indeed cracked.  if it wasnt i
guess i would of put the new one in anyhow.  it was a bit tricky puting
the new one in.  just remember to put the grommets in the tank before you
put the grommets on the Y's.  i think i put some fuel hose on the Y's
before puting the piece in too.   i also bought some graphite to help
slip the Y's into the grommets.  be careful no to push the grommets in to
the tank.
so you need to buy this breather tube and 2 rubber grommets and some fuel
line and clamps(i dont think the lines need clamped, but it cant hurt).
feel free to drop me a line after you've looked in the bentley at the
pictures there.

blake
salt lake