EF1000 hunts

This problem began to appear last summer. This generator is lightly used - 4-5 time a year, in a clean environment and each use amounts to burning maybe a tank of fresh fuel.

I began noticing the generator would hunt pretty wildly if a load were switched on (like a thermostatically controlled heater) or the unit was lightly loaded (such as an incandescent lamp) and in the economy mode after warmed up and running with the choke open.  The engine would go from near wide open to almost stall and back without end unless I pulled out slightly on the choke.  Of course the choke will slowly vibrate back open,  and the problem may begin again.  Obviously the output voltage is varying all over the place while this is happening.  If the choke if held slightly open none of the above occurs.

It seems the engine could  be running lean, or making it run rich helps anyway.  I know the available fuel around here is now all up to 10% ethanol and I heard from a friend who is a forester that they were having lean run issues with their small 2-cycle motors after they started using the reformulated gas. Since these engines dont have any ability to detect and compensate for Lambda changes caused by fuel formula changes, it would make some sense that it could be running too lean but I am not sure if this is related to the generators behavior or not.

My question is, can the hunting be compensated for with an adjustment?  If so it something like that in the service manual? If not is there something else that needs to be done? Thanks.