Disconnect the rod from the carb and loosen the nut or screw on the choke butterfly and remove the outer sleeve from the GAV and drip a bit of light oil down into the actual needle, then reassemble backwards.
If you really feel adventurous, remove the whole needle and do a little light oil on the threads.
EDIT: IF you really want to remove the GAV valve itself, an 11mm deep socket will fit, otherwise you may strip off the corners if you use a 7/16
It ain't brain surgery. Because of the crap gas they get a bit dried out is all.