Maybe this is a stupid question, but is there some kind of trick to turning this thing? Use the screw or the black plastic ****? Neither one seems to do anything but turn and then spring back ... I must be missing something here.

 

You turn the plastic piece. If you turn it one way or the other and hold it for a few seconds you should see a difference in your idle. Don't be afraid of turning it the spring is there for a reason.

 

Idle adjust screw came off my bike. I can see it hanging down with the spring. Is that an easy fix?