I have noticed that I can reduce or exacerbate the wobble by means of the throttle which could possibly indicate that an imput from the shaft drive is causing the frame to twist.
Certainly the throttle can induce all kinds of issues, as well as ham-fisting the clutch and brake. I've been paying much closer attention lately to how I operate the controls.
I really think if a few owners can do the tests I did in my videos, I could get some baseline idea. I am beginning to think that there is just enough fork play, combined with handlebar flex, plus the softer Shinko 230 (with sportier profile) that the front end is over-sensitive and a little sloppy.
Some parts of the 85 forks, such as copper bushings, are not replaceable. At least I can't find their part numbers. If they are indeed too sloppy, only a swap with the newer front end (triples, forks, brakes, fork brace, etc.) may solve the slop.
I can easily feel the frame and swingarm limitations at speed in curves. But what I think I can feel happening is the sloppy front end just starts the problems, which then get translated through the frame and to the rear. The problems may then translate back from the rear swingarm and suspension and frame back to the sloppy front end. So I feel like I need to focus on the front end first before walking backwards again.
By sloppy, I mean the front end feels too flexible. Sloppy doesn't mean loose bolts. Everything is tight and torqued. No low speed wobble at all. I can remove my hands from the bike and hold a nice line. If it were possible to ride 110mph on a flat surface in a vacuum, with NO inputs, the bike might track just fine. Any slight input from bumps, wind, buffeting, lane changes, or riding position changes can and do induce the uncomfortable onset of weave/wobble.
The most recent test was to experiment with only rear tire pressure between 30 and 40psi. Higher pressure seemed to make the problem worse. One other thing I noticed is when I removed the ME880 rear tire and compared it to the Shinko 230, the ME880 was a heavier and thicker tire. I think the 880 for whatever reason looked like it had a more robust cross section. The front tire was similar. Yes, I actually cut into the tire with a disc grinder and observed the cross-section. The ME880 tires were thicker.
I don't dare lower the front end. From everything I read about steering geometry, and from the article I posted before, lowering only the front end might make the bike less stable at speed and more performant in turns. It also may shift more weight to the front end. I've found the bike seems more stable by shifting weight rearward, but no 2 bikes are identical I guess:
"The bottom line here is that the more rake and trail we have, the more stable the bike will become, although both steering and maneuverability may suffer for it. Conversely, when rake and trail are reduced, the bike will steer quicker and become more maneuverable, though it’s usually at the expense of stability."
I can try to firm up the bars and grips to take some of the springy behavior off of the steering head but that won't solve any slop in the forks.