Probably idle speed. When do you drive your bike? If it's cold (<4 degrees Celcius) and wet you may have carb icing which will kill any chance of it idling at stop lights and make anything under 2500 rpm a little crappy but I dont think this is your problem.
The idle adjuster is between carbs 2 and 3 in the middle of the bank of carbs, you turn the adjuster clockwise(usually increases idle) or counter-clockwise(usually decreases idle) to adjust the idle up or down.
1996 bank of Bandit 600 carbs. Number 35 is the adjuster knob which would be at the rear end of the carbs between 2 and 3 (middle)
Try this, when stopped try opening the throttle just enough to make it idle ok when you do this is it fairly smooth within the limits of the skill of your hand trying to make it idle? If so it's probably just in need of adjustment.
When you start your bike in the morning cold and on choke. Adjust the choke untill you get a fairly steady idle. Then while it's idling by itself go in between the bank of carbs and turn the knob back and forth untill you can tell which way you need to turn to get the idle to increase in speed. Then when warm just adjust the idle up untill it's around 1200 rpm +- 100 rpm and have a nice day!
Here is another pic of the knob, it's a little blacked out but you'll get the gist:
Hope this helps. Remember Idle speed when fully warmed up should be around 1200 give or take 100 rpm.