He might just have too much slack in the cruise cable. Have him take almost all the slack out of the audiovox servo cable. Make sure the throttle still closes all the way. Go for a ride.
If that doesn't work he can change the sensistivity settings. Most bikes are set for medium, he can try the high setting. The tradeoff is the bike will be jerky at low speeds. He can run a gear higher than normal to soften the jerkyness
Read the audiovox manual over at murphs for the dip switch settings:
http://www.murphskits.com/catalog/docs/cc100_ins.pdf