Have you attempted to look at the carburetor to see if the main jet is removable?
If it is and you can identify what size main jet you currently have, then you can easily purchase a group of smaller main jets, trying each until you find one that works well.
The Honda Trail CT90's had for most years a push/pull slide to change the amount of air entering the carburetor for high altitude operations above 6,000 feet ASL. The last few years of the CT90's and the later Honda Trail CT110 models didn't have that push/pull slide and instead required a main jet in the carburetor to be changed down two sizes. That was the only modification required to operate the Honda four stroke engine at higher altitudes.
The common parts source for motorcycle jets is Jet R Us.
However, just search the web and you'll find lots of other jet sources, even Amazon.
Might be worth a look see.
Or, sell the Cat INV2000 to someone in Florida, next August, right before hurricane season.
I understand having to procure the necessary parts, and that looks like the route I’ll have to go. I did the very same trial-&-error rejet process with my ‘67 Jeep M715.
The thing is, I didn’t buy this generator looking for another project. I have plenty, some fun (above Jeep, IH 4x4 dually/Alaskan camper RV), some not so much (ongoing maintenance on gutter trailer & the truck that pulls it), and footworking a generator rejet is an unwelcome addition to this list.
Besides, this really wasn’t the point of my original post. If Caterpillar was the latest gofundme startup, I could have some compassion for a ball-drop like this, but they’re not; they’re a multinational corporation completely capable of avoiding such customer service snafus— they just chose not to, out of sloppiness, or whatever.
I happen to be capable of throwing together a remedy for this, but a lot of potential buyers of one of these generators aren’t, and they’re who I was trying to help out by posting this thread.
Thank you very much for the jet source, BTW.