[cadillac_al]

After reading this thread over again, I think the '70 might have had a bad coil too like Bill suggested. A compression test would have ruled out the stuck/burnt valve. I did have a brand new chrome coil fail on me once and the car ran so terrible I thought it was dead and parked it. A couple years later I went to put that new chrome coil on another car and it ran terrible too. I put a new coil on the old car that I parked and it ran like a champ. I always thought a coil either worked or didn't work but I found out they can barely work and make an engine run very badly. Too bad we didn't try that before you sold it. I love a '70 Cad. The echo down the exhaust pipe did sound like a burnt valve to me though. Good luck with the '68.