Motorcycle Repair: 1992 Kawasaki Vulcan 500, kawasaki vulcan 500, maintenance periods

Question
When the engine RPM's get to a certain point the engine will race and then not return to idle speed for several minutes.  THis happens when the bike is in neutral and stationary, or when riding.  WHen riding there is a significant loss of power and sometimes the engine will backfire.  Also when riding and this occurs the engine will race even if the throttle is fully disengaged.  This is not an occasional problem, it happens everytime the engine get's to a certain RPM.

Answer
Tim,

Without knowing any history of maintenance, periods of storage, or other helpful details, I suspect a throttle/choke cable is improperly routed or binding, the carburetors have varnished and need thoroughly cleaned, or an intake air leak is present.

Respectfully,
Mark Shively