After doing the oil change on my bike yesterday, I let it idle while I was sitting next to it and I heard a pst, pst, pst sound coming from the carb area. After scientificaly applying pressure in different directions to the carbs I found that it was indeed a vacuum leak between the carb and manifold. I removed the carbs from the rubber boots and found that the nozzle for the carbs (the peice that threads into the backside of the carb) had worked it's way loose a few full turns and was letting air bypass the metering jets. The idle had been a little rough lately and when I put it back together I had to turn the idle up a bit. Makes me wonder how long it's been running lean like that. BTW, I found that both of the nozzles were loose.