Re: Hesitation when hitting throttle...where do i start?
Been down this same road with both Holley and Edelbrock..... here is some quick stuff:
Timing - set your initial based upon cam duration. Several references on the web for this. I have around a 230 duration cam, and my motor likes 14 to 18 degrees. All in before 3500rpm, 36 degrees total centrifugal + initial (or 32 if fast burn heads). Some motors want it in quicker - I do not know the magic behind this, but changing springs and test driving is easy.
Keep the vac advance modest - 6 to 10 degrees max. It does go away with a pedal smack - so should not be a contributor. BUT.... if you are relying on it for idle rpm (and a lot of it, more than 10 degrees) then when you punch the pedal you are losing more than 10 degrees of initial and it will create a stumble. I actually disconnected mine while dialing in the timing and carb, then reconnected when I had things nice. I only have 6 degrees of vac advance, but I have vortec heads so had to keep a close eye on the upper limit.
Make sure floats are set correctly - Edelbrocks are almost always wrong right out of the box.
Idle mix is important! When you get things better, rock your idle mix a quarter turn lean or rich and check for performance.
Transition slot is important on both Holley and Edelbrock (more so on Holley). Should be a square exposed. This may give you the wrong Idle rpm, which you can change by adjusting the secondary opening (slightly) on a Holley - never did this on a Edel. On the Edel I moved the intial timing slightly to get 750 rpm idle. Transition slot only matters for off idle stumble - if the stumble happens while smacking the pedal while cruising, then it is not a transition slot issue.
Edelbrock air valve - wire it shut (temporarily) - easy to get a lean bog. I have a AVS and can adjust the air valve - I have tightened it and it still opens when revving at idle! I need to tighten a little more. I believe folks end up adding a weight to the 1406 to keep the air valve closed longer.
Edelbrock pump squirt is pretty limited in adjustment. Magic to the arm height (can be found on the web), hole to adjust squirt length and pump shooter nozzle.
In the end, the edelbrock has a needle enrichening system controlled by vacuum and springs - adust the springs to match engine vac, then jets and rods to control cruise and power mixture.
AFR meter works wonders. I used an LM1 on mine, and it helped me dial in pump shot and mixture. Do not use the AFR to set idle - my experience on about a dozen motors is that the idle mix wants to be on the rich side of life for good off pedal performance. Nothing crazy rich, but 12.8 to 13.5 instead of the magic 14.7.
Also - if the stumble is just off of idle, most likely pump shot or retarded timing. If the stumble also occurs from pedal smack while crusing (2000 to 3000 rpm) then it is most likely the air valve opening prematurely.