Holy poop on a stick.
I finally threw in the towel on the Sherpa. A kind friend offered up a contact with a trusted mechanic and I jumped on that. Why not. I figured that two hours of expert time would seal the deal. Either it was going to run for him or not. I dropped it off last week.
Two hours later (right on schedule), I had an answer. I was assembling the slide diaphragm the wrong way.
I was just dumping the slide into the bore and sealing the diaphragm into the groove, inserting the spring, and fitting the top cap and bolts. Well…. It turns out that you are supposed to hold the slide open while doing all of this. Holding the slide open allows the diaphragm to fold up properly in the vacuum chamber. Installing it the way I was doing it caused the slide to basically stick shut and the constant vacuum effect was not able to materialize.
I would have never figured that out. I’m searching through manuals now to see if it is something written down somewhere that I should have read and followed the instructions on. The mechanic said that it is just a fact of CV carbs, a sort of apocryphal knowledge.
This explains how the bike ran once – I probably was goofing off and held the slide up without knowing it was important.
Whatever. The Super Sherpa runs once again and I rode it home. I’m happy. I might even try to do the rejet just to prove that I can do this crap. I also now have a resource when I need it – a great mechanic who’s nice and fun to talk to, too.