bouncing timing mark

Not the distrib...I don't think. Accel Street Billet. Mech advance is just about perfect. Guess maybe everything else mentioned could be the culprit.
Can't remember if it's more stable at higher RPM or not. All my advance is in by 2500 RPM. Maybe I'll throw the light on and check it at 2500.
It's a 4 speed. Won't idle much below 875 or so and REALLY lumpy that low.

Anyhow, it's running pretty strong so I shouldn't let it bother me but.....you know how it is.