Edelbrock 600 carb issue?

Tried accelerator pump lever in all positions systematically and it does not fix. Have also tried covering the carb and that does not fix. It does have 1 step up on primary jets which I did years ago when we dyno'ed it early on after the v8 swap and it's run fine in its current configuration for years. Took it to a buddy's earlier and we fiddled and twiddled with it for a while with some sucess - the hesitation is still there but less severe. My friend is thinking ignition and not carb. Replacing cap/rotor/plugs/wires later today and will report back. If that doesn't help I'll get the calibration kit and change the step-up springs. One thing at a time. Thanks again everyone for the input!!!
-Tim