sheesh, not everything needs a frickin double pumper....

it's lean on the cruise circuit and/or too much advance on the cruise circut. on top of the carb, there should be 2 little metal plates held on by screws. are they flat or humped? if flat, they were changed to AFB parts, which will make finding replacement needles much easier. loosen the screws enough to rotate the cover out of the way and pull out the piston with the rods attached. if the rod does not have the dimensions stamped on it, take a caliper/mic and measure the diameter of the big diameter and the little diameter. if you have the humped covers, try calling some of the carb places (maybe demonsizzler on the board) and tell them you need a rod 1-2 sizes smaller on the big end and the same size little end for an AVS. or try buy some new flat rod covers (for an eddie AFB) or make your own out of some flat metal. now go look through the edelbrock catalog, find a rod with the same small diameter and 1-2 sizes smaller big diameter than your rod.

that will keep your power calibration the same, but richen up the cruise calibration slightly.

you could also try disconnecting and plugging the vaccuum advance from the distributor and see if that helps, but I doubt it, I think it's more that it's too lean at cruise with the upgraded cam.

another possibility, it could be the carb getting too hot. do you have a 3/8" thick insulator gasket between the carb and the intake?