I've had my EF100IS several years, always working smooth and reliable. This summer while recharging my coach batteries it started the surging/hunting (repeatedly RPM cycle down-up-down) engine speed when in any mode. The surging/hunting went away with the choke out a small amount.
When I got home I pulled the carb and cleaned it three times with cleaner, and I passed a thin wire into every fuel passage. It got better but did not stop the hunting till I backed the pilot screw out about two turns from the factory setting. I even removed and cleaned the spark arrestor screen and replaced the spark plug, which made no difference.
Frustrated, I ordered a new carb. After installing the new carb it repeated the surging/hunting cycling of engine speed just like the old carb before backing out the pilot screw. The new carb has a metal casting around the pilot screw so it is not as easy to defeat the factory setting. The new carb smoothed out after pulling out the choke a small amount.
I would think that applying a little choke to create a smoother running engine would be diagnostic of a lean carb. I would expect the new factory carb would have been set up to run the generator properly.
Anyone got any ideas on what else could cause the generator to repeatedly RPM cycle down-up-down?
BillOfSpfld, You are correct about the partial choke causing smooth running as indicating a too lean carb. New carb or old, it is telling you the truth. In addition to a too lean slimy pilot jet orifice (even on a new carb!), it can also mean a bad gasket or a warped/gouged gasket surface allowing a mixture leaning vacuum leak. Even a tiny vacuum leak can have a big influence, especially on Eco-idle or full RPM light load small throttle openings.
I noticed when recently doing a carb clean on my EF1000iS (new Dec 2009) that care is required when re-installing the carb because the cooling shroud interfered with the carb gasket and that there was a cautious sequence of operations to follow so the intake gasket is not damaged and is properly positioned. Also check that the air filter is not cracked/crumbled, installed out of place or eaten by critters. It should also be oiled (about a level TeaSpoon), squeezed in a plastic bag to equally distribute the oil throughout, then squeezed again quickly in a paper towel or rag just to remove the excess oil.
It is because the 50cc engine is so small that the carb pilot jet must also be very small, making it very likely even well cared for EF1000iS Gennys will eventually need a carb clean. I run mine dry, fuel valve off for almost 4 minutes, using increasing partial choke to maintain smooth running until the carb jets suck air and the engine stalls out with nearly full choke. Then I drain the float bowl and store it in my humidity controlled basement. Even after that and always using stabilized fuel, one of the times I really needed it, it would not run well because the tiny-tiny pilot jet orifice got a restrictive film deposit. EF2000iS to the rescue, the EF1000iS set aside for the carb clean.