timming jumping around?

If you are useing a MSD ignition box you either need to use msd's timing light or a old school timing light with out the advance dial. Just use timing tape or a aftermarket balancer. I went through the same thing last year. I tryed everthing posted here. It was driving me crazy for weeks. I finally used timing tape and left my advance dial off and it was perfect. I think msd changed something in there box because I have two other cars with older msd box's in them that I never had a problem with. A friend also had the same problem a few weeks ago and his msd was the same way. Good luck.