Honda Gl1500 Idle surge and carb question.

Engine RPM surges up and down while at idle. Engine runs rough and hesitates on takeoff. Bike has set up for a while, but had fuel stabalizer in it. Seems like a vaccum leak I think. When I put my finger over the taller of the two brass fittings in the carb venturi (the ones that come straight up not the accellerator pump fitting) on the right or left carb the engine smooths out and idles normally. However if I plug both of these holes the engine misses and idles rough again. If I plug the hole in one of the fittings with a toothpic the engine does not hesitat on take off. What is this brass fitting and what am I changing when I put my finger over it or plug it with a toothpic? Does this indicate a carb problem or a vaccum leak?