Onan 4000 Revs up and Down

I could be a too lean condition and require an adjustment of the altitude adjuster. The surging could also be caused by a bad adjustment of the idle speed screw. It's on the carb next to the throttle wire. It should have a small clearance when running at idle (3600, no load) but if the clearance is too large, it will cause hunting because the carb goes below idle at load off. If I remember right, the screw is adjusted to produce 90 volts when the throttle is held against the screw. USE THREAD LOCKER ON THE SCREW WHEN FINISHED ADJUSTING.

JimL