episodic revs

Hey folks:

Working on a friends 79 KZ1000 and everything is excellent.......except this:

at various times bike wants to move from idle to 5K rpms. The carbs are VM. In addition, this happens when riding. It is as if the slides are sticking but they are not. When the high revs occurs I can usually get the machine back down to idle with a hard-quick crack on the throttle. Anybody have any idea what might cause this strange behavior. (Mixture screws are correctly adjusted and the carbs are sync'd).

Thanks for any input you provide: dtkid

There are a number of reasons this can happen:

weak return spring
throttle cable tight
air leak in emissions system/hoses
air leak in vacuum cap on vacuum port
air leak in mix screw oring
air leak in carb holders; either crack or bad seal
re-use of exhaust crush gaskets
throttle sleeve binding
ignition timing off
mechanical advance on ignition sticky; clean/grease
throttle cable mis-routed and binding
one or more emulsion tubes deformed from over tightening
other binding such as shaft that actuates slides

thanks george