I noticed mine had quite a bit of end play. I could pull the rod out on the advance side and see it move. When I released it, it snapped back in with an audable "click".
I thought this might be happening while it was running and adding to the top end clatter. It wasn't easy to measure, but near as I could tell, I had about .015" end play. I shimmed it down to about .005". You can't go too tight or the advance rod won't advance - it will bind up when you tighten the disc down. Check it by rotating it by hand.
Well, this didn't do anything for the top end noise but the bike seems to run
smoother. Now with a timing light, the marks don't seem to jump around as much.
I think this stabilized the timing and the advance curve a little bit.
A buddy of mine stamped me out a few shims at work in various thicknesses. I was
ready to buy some from McMaster-Carr and now that I know they do something, I
just might. A standard 1/2"I.D. size works. The rod is 12 or 13mm O.D. (I don't
recall exactly). They have metric ones in 12 and 14mm I.D.s but these only come
in 50 pks., way more than you need. The American sizes come in 10 pks. A pack
of .006"s and one of .002"s would allow you to shim from .002" up to way past
.020" in .002" increments. The 2 packs would cost you about $8, just like
buying a set of points. With the rod removed, place the shims on it behind the points cam. Re-assemble and check by hand for binding and end play.