JD RX75 engine surges when no load

I have a JD RX75 with a 9HP Kawasaki engine. It starts easily and runs okay except the engine surges at all throttle positions when there is no load. If I start driving up hill or engage the mower deck the engine runs smooth. But as soon as I push in the clutch or go down a grade the engine starts surging.



Does this sound like a carb adjustment or something going on with the governor?



Any recommended corrective actions?



Thanks!