Replacing Governor Spring

Thanks for the replies. Neil, yes there certainly are a lot of variables and the age factor is a complication. I do have a quite new carb on it, and have recently decided to be more aggressive with exercise... more frequently and more load during. That in itself probably is the most important thing I have ever done for it.

JD, thanks also for telling what you have experienced. I'll make the spring replacement, now that I have it, and will take it from there. It was a very inexpensive item and can't hurt, for sure.

Our similar but I believe older ONAN BFA ("4KW RV GenSet") was hunting. After I had the carb professionally rebuilt. The manual's flowchart included "replace governor spring" after a number of other steps. The Cummins/ONAN shop was on my way to work so I stopped and got a spring. Installed and no more hunting. At the shop, they explained how the spring sits stretched year after year and can get just a pinch out of calibration.
I didn't have to adjust anything. If your genny is plain old fashioned like ours was, I don't think you'll have to either. If you get the carb mixture settings right, you might want to adjust Idle RPM. Manual says to go by 1800 RPM or 60 hZ. On the BFA, setting idle based on AC voltage accomplished the same thing. I think I set 120 VAC at no load idle. When I say "idle" that means the Throttle Plate is in Idle position and the Idle circuit of the carb is delivering the fuel. When you add load, the governor (and that Spring!) hold the RPM, but the carb throttles up and the power circuit is delivering fuel.

Most all gen sets will hunt/surge at some point, but knowing small engines like I do, most of the time it is never from the gov spring, gov setting maybe, but not the spring itself unless someone has had their hands on it.
These 4 stroke engines, can be temper mental when it comes to the proper amount of fuel being supplied to the engine. For instance on start up everything is cold & the fuel needs to be richer for the engine to start up, but it can get to a point where its getting to much fuel & then the engine will not start, so at that time the conditions have got to be close to perfect.
Now add in, say like the valves are just slightly out of adjustment, not enough to see unless you pull out the feeler gauge & measure, so that is adding to just making the engine even more ill when starting up.
Ok, say it cranks up real good, you dont have to zoo & zoo the start button to get it to crank up, well that is pretty much telling you the engine fuel is just a bit rich so it starts up fine.
After that & the engine has ran some, that carb adjustment didnt change & is still providing just a bit more fuel than the engine will need once at operating temps, so its operating in a rich mode.
Now add the gen load into the mix, that sort of richer mixture than needed comes into play, because under load the engine will need just a bit more fuel to maintain that load.
Lean the mixture out some or either richen it up some more & you'll get that hunt or surge & the same can happen when you shut things off that are using 110 V a/c & will take a second or two to for the engine to adjust & level itself out.

Add this into the mix on top of everything else, old fuel pump, old dried out or soft fuel hoses from the tank to the gen set pump & then the inline filters before the carb. Any restriction from any one of those things, can cause the engine to hunt or surge trying to maintain that engine speed to keep up with the a/c load.

Ok, now I'm fixing to really jump on some nay sayers feet now, Ethanol gas.
You can beat a dead horse to death, with saying nothing wrong with this E10 pump gas we have to use, but that small gen set engine cant deal with it over time. Theres two many things inside that engine & carb that are not designed to deal with it & end the end those parts will fail.
Now this up to date stuff sold today, computers & fuel injection systems on engines today, can adjust to the use of it, but that small engine is as old school as you can get & it cant adjust on the run like that computer controled engine can.
Neil