Re: clutch thingy?
You really don't. The older machines had to have the secondary disassembled to make that change. The dial just makes adjustment easier, particularly for racers trying to get the best holeshot possible. When your belt wears you should put on a new one anyway, then your back to square one. Mountain riders may pull the belt out a bit more so they have a lower "first gear", that sort of stuff.
I wouldn't mess with it if your just riding, mostly because if it's set right (with a new belt) you don't need to.