Problem: Champion 3500 generator (like this one sans electric & remote start) began surging/idling up and down intermittently and consistently during operation after the first twelve hours of operation.
Diagnosis: Main jet/nozzle is too tight/restrictive due to EPA restrictions.
Previous repair attempts: Brand new carburetor, flushing both carburetors, SeaFoam, different types of gasoline with different additives/treatments. Note: Champion power equipment is generally very well known for their superior customer service, but such was not the case for me.
Fix applied: Drill out the main nozzle on the old carburetor using a Dremel tool and first, a .028/#70 bit (this worked fine & I probably could have stopped here), then a .029/#69 drill bit. I used this $4.46 drill bit kit from Amazon.
Results: Perfect operation, no more erratic idle/surging idle. One pull start on months to over one year old 87 octane, Stabil treated ethanol gas. This method worked and I believe that many people whom have given up on their small carbureted engines should try this.