What did you set the timing to?
What's the specs on the engine.
I don't ever run the vacuum advance on my car, just use the mechanical, and I pull the heavy advance weight out so the advance comes in earlier.
I run a total of 36deg timing on my 440.
1968 440 comp cams 268h-10 cam 268 lift 218 duration(very smooth) 750 holley on a wiand dual plain intake schumacher headers ,TTI exaust,3.91 gear in a 8 3/4, timing is set at 38deg@2500