If the idle seems to be right, then your problem is likely in the clutch spring or bearing. There is no easy adjustment screw for the clutch, you have to take the engine out or take the fuel tank off to get to the screw that holds the clutchbell on. Because it is a bit more work, I caution that you make sure it isn't a high idle condition causing it to roll forward while idling, before you look into the clutch.

Once you are 100% sure that your idle isn't too high:
Remove the clutchbell and check the roller bearing and shims. Make sure it all looks good, rolls smooth and nothing is binding.
If the bearing and shims look good, chekc out the spring around the clutch shoes. It needs to be pretty tight to keep the shoes from engaging at low RPMs. If it seems loose, then you will want to shorten it a little at a time, chekcing to see how your changes have affected the engagement of the clutch between each small cut.

Basically all I did was took the spring out, nipped 1/8 of an inch off, twisted the ends of the spring back together, reinstalled it, tested it and repated until I got it engagin the way I want it to.