So, I noticed the idle decaying today when I was out riding the GS. Did some looking in the FAQ section, and found the part about "both carbs leaking fuel" after I shut it off and saw fuel draining out of the air box (which was definitely wet inside with the air filter removed).
Took the tank off to get to the breather tube, discovered that the PO removed it, though the T fitting is still there. Air blown through it makes both carbs drain into the airbox, pretty evenly. With the gas tank removed, the idle was fine with what fuel was left in the carbs. Connected everything up, and left the air filter off so I could see what happened with the fuel flow back on. The right side carb leaks into the air box, but the left side doesn't (completely dry, in fact). Bike runs fine with throttle, it's just idle that's a mess. I'm guessing the two little holes on the bottom of the carb are the idle circuit? Before I go and take the carbs off, am I likely correct that the float on that side is sticking or busted? Is there anything else it could be?
If I'm going to take the carbs off and do work on them, I'll probably rejet them and put a lunchbox on them instead, so maybe this is just the excuse I need, but I'd like to solve the problem the first time.