There should be two screws on the left side. One is larger, that is the idle screw. the very small one that is almost flush with the carb body is the air screw.
The air screw should be around 1.5 turns out,(counter clockwise) in the standard setting. Turn it in being careful not to tighten to tight, that will damage your carb. Assuming that your bike is jetted properly you can fine tune your throttle response by turning the idle up a bit faster than normal and adjusting your air screw between .75 and 2.5 turns full the seated position to find your highest idle. Once that is done you need to re set the idle with the idle screw.