Why the gas engine hunting while running?

Regarding to my experience ,there are some possible cause for this issue : 1. Engine : Death Ignition /Spark Plug,which is lead to unbalance power on crank shaft.Long term operation in this situation might lead to broken/damage shaft. 2.Low pressure on 1 or more combustion chamber,due to leaking on piston rings.It is also could make unbalance on mechanical operation of the engine. 3.False setting on Actuator,which lead the false response/compenstion time of the fuel demand. 4.Broken governor ( false setting) : try to adjust the gain and stability setpoint. Please note : Adjust engine stability first by set-up gain & Stability.After stability obtain,adjust the speed to the nominal speed ( ie : 1500 rpm).Initial speed setting is the factory setting,so it won't far enough from your nominal setting point. 5.Bent actuator linkage ,it is causing the compenstaion curve is not in good order.Please check for the linkage. 6.In case of the engine is the prime mover of a generator,electrical cause might lead to this situation ; ie : unbalance of excitation on the field winding.The possible source could be ,unbalance value of the insulation which lead on unbalance magnetic flux. Hints : on AVR ; try to adjust STAB ( Stability ) setpoint if available. 7.Ground faulty on speed input device ( MPU = Magnetic Pick-Up Unit ) .Check the +/Ground impedance value and compare to the -/Ground impedance value.It should not to be zero.That's why it is better to have coaxial signal cable on this input,to avoid any ground noise.If you have power analyzer,check for the signal noise. Last,but I hope it is not the last clue is mechanical damage on flywheel,which leads to bad signal from MPU.manually rotate the crankshaft and see the condition of the flywheel for any mechanical damage posibility. For initial action : try to disconnect the engine from the driven load.See; if the hunting is gone ,the hunting must be comes from the load side.But if the hunting still present ,it must be comes from the engine itself. Have a good Troublehooting bro ^_^ iWe - Borneo