Many little carb facts

[mikenixon]

I've never had the plates off of their shafts but I'll try to remember to look for that when I can get at it again in the spring.
I was wondering if wear where the shafts pivot could cause it?

The plates drift. No reason other than the very low tech way in which the shafts and plates are assembled. Carb rebuilders see this a lot.

I thought the rings might be cushions (like the plastic buttons in 1000 carb tops and the plastic pieces in the tops of the shafts of the slides in the 1100 and other Keihin carbs) but are they wide enough to catch the edges of the slides?

The plastic rings are slide cushions, merely preventing slide to body contact. They also serve a tuning function. Note that every model has its own ring specification.