1981 C10 dies when I let off the gas

Just installed "new" used quadrajet on 305 1981 Chevy Silverado. Motor starts and runs strong as long as I have my foot on the gas, but dies as soon as I let up. Also recently replaced: electric fuel pump, ignition coil, plugs and all filters (inline and otherwise). Ignition module checked out ok.

This is a fairly straight forward motor - but I'm running out of things to check. I've got good fire, plenty of gas to carb, and as I mentioned, motor sounds good and strong. This is actually an improvement, as truck would not start until I replaced carb, so feel I'm headed in the right direction - but I've got to be missing something.

Any helpful hints from you Chevy afficionado's out there?

try to adjust the screw by the throtle it might help