Its probably just the carb idle adjustment, but a little more engine information would be useful. A large cam and low vacuum can make idle mixture adjustment more complicated.
If its a relatively stock engine, just follow Edelbrock's directions and get a good idle mixture (2-3 turns out from seated is usually a good starting point). Then adjust the idle speed so it runs about 700-800 rpm while in gear (if its an automatic). That should be high enough to keep it running at a stop light.