We use a Honda 1000, which has been a great generator. It's a generator since it generates electrical power, which then goes through an inverter for a 120 VAC, 60 Hz output. I don't know if the first stage is DC or AC, but I suspect DC, since converting it to 60 Hz AC at various speeds in ECO mode would be a lot simpler.
That discussion aside, the one problem I've had with the generator is the servo sticking. The carburetor is servo controlled by the inverter, and the servo motor is bolted on top of the carb. A couple of years ago, I replaced the carb because I couldn't get it to run smoothly at low output in ECO mode. Worked well for a year then started surging again, so I sprayed the servo motor with silicone spray, which cured the problem.
I realize the your problem is low output, but I'll bet that's because the the servo motor is sticking utill it gets a large signal from the inverter, and then opens. BTW, you didn't say if it'll output power under a large load in ECO mode. I assume it does. So probably after 6 years the lubricant in the servo motor is coagulated. Try spraying silicone in there and see if it responds. Switch a 100 watt bulb on and off, that should shake things loose.
Cleaning the carb can be done without pulling the thing, at least on a 1000.
Those are great generators. The 1000 will run a 5000 BTU air conditioner with no trouble. Though, I'm not certain I'd be willing to go where I needed air conditioning in the boat.
Boris