Ok so I was riding my 86 vn750 a few days ago and realized I was maintaining 40 mph with the throttle closed. I pulled the clutch in and the RPMs jumped to 3 or 4 thousand. I got it home, messed with the idle screw and throttle cables and it didnt help. When I turn the idle screw down eventually it dies. When it is running in my driveway it will idle fine around 1000 but periodically jump up to 3 or 4k for anywhere from 15 seconds to a minute, then come back down to normal and it will just keep up this process for as long as I leave it running. I watched it pull these cycles for 20 minutes today. The throttle doesnt seem to be sticking. I am clueless to what may cause this. I am generously mechanically inclined and capable however I am relatively new to the motorcycle world. Any hints, suggestions, or input is much appreciated.