Beyond all of the things which aren't technically correct with my particular set-up, I have a couple simple questions relating to derailleur function only. The first is this: Suntour Cyclone & Cyclone GT Cages c.1980 In the top view, what is the purpose of screw # 23? I came around to this in trying to figure out why the derailleur itself is making so much noise--seems unrelated to the obvious chain issues. I could be wrong, of course. In my case it's a Suntour VX, but the screw in question is the same.