I finally got it! At last, the clutch is working correctly. Don’t know if I truly found and fixed the underlying problem, unless it really was just the cable adjustment. I sure went about it the hard way, though. Now that I have a shop manual for my bike, I see that adjusting the clutch cable is much simpler than I made it. The official instructions do not include threatening the cable with replacement, although I think ultimately that’s what worked. Replaced the tach cable, too, which is a relief. The speedometer cable I bought was not quite right. Thought I could get it to fit, but no luck, so I ordered a new one from Yamaha.
As of today, I also have changed the oil myself — the darn viewer window is so hard to read. I once again had too much oil in the bike. I had intended to drain about half of it, but, well, when you don’t really know what you’re doing, interesting things happen. I now know more about motorcycle maintenance than I know about maintaining my 2001 Exploder. Ordered a new air filter, too, since when there’s too much oil it gets forced up into the air box, fouling the filter.