What could cause Carter AFB 9605s to run lean under load
 

I'm stuck, I've rebuilt the carb, got the calibration kit tried different combinations of rods jets springs and nothing with fix this problem. It's a 600cfm on a 440 with edelbrock intake. Is it too small of a carb for the engine? Bad fuel pump? What else could cause this? It idles perfect, but when I take it on the road it seems like it doesn't have the power it should, the plugs are clear white after a drive but tan after sitting at idle

Carbs too small

carb is too small for a 440, also I suspect it was jetted for a GM application when new