Edelbrock 600 carb issue?

Have you changed the metering rods and step up springs? They make a kit for that. I changed mine on my carb (it's a 1406) just like yours. It made a world of difference. Also there are 3 different positions you can adjust the accelerator pump. Have you looked at that. Mine was set at the top and it was getting too much fuel. I moved it to the middle and it's running a lot smoother with no hesitation.