My 77 CJ7 has run for years without any attention, not that I put any great miles on it. This summer it decided it was going to be difficult, so now I have to remember how a carb works, with very small success.
I took it all apart and cleaned it, and blew out the jets. Put it all back together and tried it, no dice. When I come off of throttle, it dies unless I very carefully feather it down to idle. I’m clueless about what’s wrong, and have run out of dead chickens to wave over the necromantic device.
I think it would be less trouble to pull the engine and put in a spare 4.0L I have on the shelf.
I can’t help with the problem since you’ve covered most of the things I would know about. Last carb I worked on was my beloved VW Beetle, and I understand how things can run fine and then suddenly just stop for no reason. But in the end, there IS a reason, somewhere.
I just commented to point out if it helps, a carburetor is just a mechanical computer. It changes the input of fuel and air based on other variables. So somewhere in the code something is now not calculating the same as it was, or the variables themselves are different. I know that doesn’t answer the problem, but it’s something I’ve always been in awe about since being told my my dad that a automatic transmission is just a fluid computer. Which is funny, since he could tear down one of those, but never could “get” how an electronic computer worked.