Well, if you back the idle speed screw out all the way so it's not touching the cable arm, both butterfly plates should be closed completely and the bike should stall .....
Are you sure you have enough slack or freeplay in your throttle cable? If it's adjusted too tight, that will hold the butterfly plates open. Even if you back the idle speed screw way off, the butterfly plates won't close all the way if the throttle cable is too tight and holding them open.
Are you sure you have enough slack or freeplay in your throttle cable? If it's adjusted too tight, that will hold the butterfly plates open. Even if you back the idle speed screw way off, the butterfly plates won't close all the way if the throttle cable is too tight and holding them open.