Make sure that you don't have the throttle grip pushed all the way up against the handlebar. After it is installed you should be able to grab it and feel a little bit of play in and out. As for cable adjustment, take most of the slack out of both cables before moving the throttle. Adjust the throttle side until you can open the throttle and see that either the stop on the "throttle plate" as you called it contacts the carb body, or the butterfly in the carb looks wide open (you will have to remove the air cleaner for this). Then adjust the slack out of the idle cable. After both cables are adjusted, you should feel a little play in the throttle. It sounds like you have adjusted the throttle side too tight and the grip in catching the housing, or the cable ferrel in the housing isn't seated right.