Little bogging

I have a 318 with headers, RPM Air-Gap, and Edelbrock Performer 600cfm carb (mechanical secondaries). When I start opening up the secondaries at lower RPMs (no tach so I'm guessing 3k), I lose speed then once the RPMs climb a bit it feels like the engine has been freed up and it'll go. It did it much worse before headers, so I'm wondering if it is a jetting issue or a timing issue. I haven't messed with either before.