carter AFB troubles

I have been working on my friend's 440 trying to cure a part throttle surge.
The engine is a 10:1 440 with eddy heads, mild crane (similer to 375 horse) cam, stock exh. manifolds and eddy performer manifold. It idles great and runs great wide open, but part throttle it surges. I have gone both ways with the metering rod springs with no improvement. I have jetted it down for our 5600 ft. altitude. Any ideas? The carb is a fairly new Carter 750.