I'm not sure if this is the same issue or not but I have a new edelbrock 750 on my 400 and I have hesitation when starting from a complete stop. I have the jet kit for the carb and have installed nearly every combo in the book and can not get rid of the hesitation. I've tried adjusting the accelerator pump also. If I put my original Q-jet back on (which was rebuilt over 14 years ago) it runs fine - not quite as strong at high rmps but much smoother and no hesitation whatsoever. A friend of mine suggested that the 750 may be too big for my set up which is pretty much a stock rebuilt 400 with an HEI. If you find a solution, I'd love to hear about it.