Turning eco off does not cause the generator to run at full throttle. With the eu2000i it boosts the idle speed from 3,000 rpm to 4,300 rpm, vs. a maximum of 5,000 rpm. Spinning at the higher idle speed gives the generator more kinetic energy to burn off until it's able to respond with more throttle when hit with a large load. Every setup is different. Sounds like you need to run yours with eco off. You could also be powering other loads like the fridge if the switch isn't on "gas only".