340 Edelbrock Carb Adjustment

When i get hard on the gas of my 340 in my 69 Cuda, it seems to release some black smoke out of the tailpipes. I can see it when i look in the review mirror. You have to really mash it to see it. It has a 600 CFM Edelbrock on a stock 340 iron intake. My personal impression is that it is overly rich, but the screws are only turned out 5 whole turns. It's not a ton of smoke, but just enough to notice when i look on the mirror. It has not been rejetted from what I had when I took it out of the box.

Other than that, it runs very strong and idles smoothly and doesn't seem to miss or fall on its face at high RPMs.

Am I correct about over richness or jetting? I have always thought about going to a 700 CFM or thereabouts Holley. Would that be a good way to go, or should I stay with the Eddie and adjust it?

Thanks