A little engine trouble, need suggestions!!

[Red68]

I recently rebuilt my sb 327, I have a edlebrock 600 (used on motor before rebuild), GM HEI ignition. I currently have about 450 miles on the engine. My problem is when I am sitting at a stop sign and let out on the clutch it almost dies, when I put my foot in it the truck takes off.

I had a mechanic work on the carberator and he adjusted the jets and it seemed to improve a little but i still have the problem.

It idles great and runs down the road really good, just starting out from a stop seems to be the problem.

Could it be something with the timing or distributor?

Thanks for any suggestions or help anyone can offer.