I'm by no means a super generator expert but I've been using and working on small generators since I was in the Army That was 49 years ago and I can pretty much fix anything. They really aren't a heck of a lot more complicated than a lawn mower or a tractor. Most of the parts are easy to swap in and out. You can troubleshoot them most of the time with simple tools and a decent manual. These Onan RV QG 4000's are the fussiest, flakiest machines I've ever had to deal with. The new Onans require constant maintenance and attention. They're potato chip gennies at caviar prices and I'm tired of fiddling with them. They always seem to break the day before you're planning to use them. The prices for replacement parts make you think you're fixing a Maserati. This has to stop.
I wish the RV Manufacturers would go to something more dependable, like a Honda or much cheaper, like a Champion. With any luck someone like Champion will design a unit that drops into a bay designed for the Onan and sell it at a reasonable price. I'd buy it in a minute.
Rant off
The altitude adjustment was just a thought. I do most of my driving at or near sea level and rarely touch it. Keep dosing it with Seafoam. Sometimes it takes more than one treatment and it sounds like you might be making progress.
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