[WadmalawJoe]

I was reading up on the vacuum advance stops or limiters and came across this explanation its pretty good and with good pictures imho
http://temp.corvetteforum.net/c3/joe..._Recurve.shtml

I think I need to pick up a kit that comes with the stop and install it. Instead of backing my timing down until it the highway tapping goes away, I just need to limit the advance to maybe 10 instead of the full 20 degree jump.
Which is basically what JoJaboy and others have been saying all along and what I have been reading. I guess I just have been trying to make what I have work, but my motor is just real finicky.

Longhair to answer your question on the current advance can, it starts to work with very little vacuum at all, maybe 3-4 inches of vacuum, its at full advance by 10 inches for sure.