When accelerating at moderate to full throttle, I get this bog that makes the car shake, once it hits about 3000rpm it smooths out and there is a very noticeable power increase. It does it in just about any gear from about 1500-3000. It's a Holley 750cfm #4160, vac. secondary, the secondary metering plate has been replaced with jets. I'm thinking it's either the power valve or maybe the secondaries are kicking in too late? What's odd is I have an A/F ratio meter and it shows about 13:1 during this, not too rich or too lean.

 

Does the car still do it if you temperairly disconnect the vacuum advance line?