I think Kent's latter suggestion is most likely. Just bend over and look at the throttle cable at the rear. If you can't see a little bit of VISIBLE slack, loosen the locknut on your cable at the SWITCHGEAR end and turn the barrel adjuster a couple turns toward you (rear of bike). Watch the cable at the carb and note when you can SEE some slack. If there is no slack, the throttle tends to hang. The other reason that a bike has inconsistant idle is air leaks in the pilot circuit. Most likely cause, in your case, is bad orings on the pilot fuel mixture screws. These orings are made or nitrile or buta rubber and they do tend to harden with age and provide poor seal. Air can leak in and idle will jump all over. Another source of air leaks is that the pads on the choke plungers harden and again, air will leak into the pilot circuit via the choke circuit. If your idle jumps up, jiggle the choke lever a bit and see if it calms. If it does, the choke plungers are the issue. See the write up on choke plungers on my web site. Last, your carbs may not be seated great in the intake manifolds or the vacuum ports may not be capped or the caps cracked but this tends to make the idle high but not jumpy.
