After the last post, went back to bed and slept until afternoon, then went outside and cut the grass. After that, started working on motorcycle.
Got everything (almost) arranged and in place before I started work. Still sitting on the floor to work on motorcycles because I haven't got a lift yet--haven't gone back to, or called, Harbor Freight since my initial attempt to buy one--and probably will not before June is out.
Disassembly was pretty straightforward. Tore the side cover gasket getting it off--I think. It might have already been torn; anyway it's torn in a spot which won't see much oil laying against it, so it ought not to leak much, if at all. If it does, I can always get (or make) a gasket for it. No big deal.
With the ignition trigger and advance assembly out of the way, and with the cover off, I was presented with the clutch assembly. The bolts that hold it together popped loose a lot more easily than I was expecting them to--easier than they had with the spare engine--and I wondered if that was related to my issue. Still, pulled the pressure plate off and had a gander at the first driving plate. It looked identical to the known-good ones from the spare engine, so I decided to go get the caliper and check these for wear.
The result was that the drive plates were all 3mm in thickness, which is well within limits. The caliper I was using doesn't have tenth of a millimeter resolution, so I had to eyeball it, but the steels were a single width of the marker line thinner than the ones from the spare were. Looking at them, I could see that the pattern of oil-retaining dimples on their surfaces were not uniform, and were worn around the edges.
Pondered this for a bit.
The springs--I measured them and found my problem: the wear limit for the clutch springs is 38.4mm. None of these springs were longer than 36mm. One (at least one) was 35. And that would explain why the clutch slips under high load conditions: insufficient clamping force. And the springs from the spare motor were all 40mm.
Thought it over; the springs were definitely bad but the steels were iffy. Finally I decided that I'd go ahead and replace the steels, along with the springs, because I did not feel like having to do this again. But the friction plates were all good--well within specification--so there was no reason to replace them.
So: used the OE friction plates and the spare steels, and springs from the spare motor; reassembled everything and buttoned it all up. Dumped in all the 10W40 I had, which wasn't enough; so I went to O'Reilly's and got more oil, as well as license plate bolts for Mrs. Fungus' bike and a set of 6-sided dice tire valve caps. Always wanted a set for the bike, so why not?
Filled the crankcase the rest of the way (for a total of 2.6 liters of 10W40), adjusted the clutch according to the manual, and then took her for a short spin--and it was night and day. I mean, the clutch takeup was smooth and not grabby, and the pressure point is in a pretty good spot.
I have some more adjustments to make before I take it to the shop, but I think we're pretty close to that point. The rear brake needs adjusting, as well as the brake light switch for the front brake lever.
I may ride her to work tomorrow, depending on circumstances. We'll see. But the clutch has been a minor issue that I've been living with since I bought the thing, and I think I got it fixed today.