Some of the bikes came with improper cable routing, causing them to bind.

Here's another simple fix to cure some annoying problems. Some of the bikes came with the throttle cables routed through the bars instead of over them. Just unhook them and swap them around. If you still have some binding, try rotating the cable housing downward a bit.

While you're are at it, check that the freeplay is right on the throttle. You want 1/16" to 1/4" of play. Check at the carb end of things to be sure that the throttle and return cables are slightly slack when neutral. I found that without the slack, the throttle liked to hang a bit, causing high idle.