Two things come immeiately to mind.
1.) Crap in the carb's idle circuits.
2.) Since you're running a serpentine drive, that means you're running an electric fuel pump. Depending on how much fuel pressure you're running, you could easily be overpowering the floats and dumping way too much fuel into the engine. Eddy carbs don't like much more than 5-5.5 lbs., Holleys can take a bit more, maybe 6 or so. Are you running a regulator, and if so what is it set at? Incorrect float height can also cause the same thing.