I suspect it's a mechanic problem rather than a mechanical one.

I tried the suggestions and the one that seems to work best is to set the timing using a vacuum gauge instead of a timing light. I guess I don't understand the markings. The harmonic balancer has markings from 0-30 BTC and 0-20 ATC. there is a machined groove at the 0 mark. The timing cover has markings from about 0-20 BTC/ATC. I presumed (error) that I align the machined mark on the balancer with the timing cover mark that gives me the specified 2 degree BTC timing at idle.

Boy, was I wrong. I had to advance the timing more than 10 degrees to get the engine running smoothly again. I used a vacuum gauge to get it into the ballpark and now the vacuum is >20". I would never have thought of that myself. It has a LOT more power, but the timing marks don't seem to have anything to do with reality. My rebuild and tune-up books don't discuss this. They just say to "align the timing marks".

I would now like to set the timing exactly to specs. Is there a secret way to do this other than the "set it 'till it pings under load and then back it off" method?

I really appreciate all the help!

Bob