If you back the throttle stops right off. the motor should still idle. I usually adjust the mixture screws towards lean until the motor coughs, then back off slightly. That way you should get a smooth idle with jetting which is not too rich or too lean. If you drop the slides to rock-bottom, the motor should not stop. If it does stop, I usually wind the stops up until I get a moderately quick idle. You need to make sure that when the slides are at rock bottom, there is still slack in the cables, and the slides are level at full throttle - if you have long bell mouths, you cannot check the slides with your fingers to see if they are level, so I usually do it by eye when the throttles are almost fully open.. I've seen some bikes with carbs in which the throttles never reach fully open. Sometimes you can wind the twist grip to it's end, but if the cables are too long, you end up with some slide still in the venturi. I don't like junction boxes.