Clutch is slipping.
...I could get the thing up to 55 MPH but trying to go faster--especially in 6th gear--led to the engine revving way up and the bike slowing down. Argh etc.
I'm going to adjust it (and of course at some point find a shop to adjust everything) but I want to see if I need to replace the clutch, first. I'm betting that's a "yes".
Well, a set of clutches doesn't cost an egregious amount of money, and I have the service manual to tell me how to do it, so I should be okay.
Come to think of it--what's the clutch like in the spare engine? Maybe I could use that one? Probably wouldn't hurt to take it out and examine it, anyway, to see if it's usable.
But it felt good to ride my motorcycle today. Really, really good.