Trying to get the initial and total timing set on a fresh 402 BBC. I'm running an Edelbrock carb and initially tried to use the ported vacuum for the v. advance. Engine ran like crap, so I switched to the full vacuum port...much better. Initial timing with v. advance disconnected is 16-20 degrees, but when I re-connect the v. advance, the timing jumps up to 40-45 degress (at 800rpm idle). I'm guessing that's because the v.advance is kicking in. (is that too much?)

However, I'm having a difficult time getting an accurate reading because the the timing marks (timing tape) keep jumping around. The timing keeps jumping between 40 & 45 degrees, so I'm not sure what the reading really is. Any ideas why it's jumping around? It's almost like the engine hits a miss every once and awhile. I could really use some help/advice. Thanks.