I have a 67 ss with a 396/375 hp. engine. Picked up a nice holley 650cfm double pumper(had a 750 double pumper on and had no problem, just thought I'd make a change) When I hold the accelerator at a steady speed of anywhere from 40mph to 55mph, I notice a slight surging rather then a steady constant movement-more like a pick up and back off of speed but pretty slight. What may this be(float problem/mixture problem) and any suggestions on the fix. I can always go back to the 750cfm but I'd like to correct this one if possible. Thanks all!