'70 318 BBD falls flat under load

Changed over the linkage and lever and adjusted the pump to 9/16". Checked the timing and everything is well. The engine still starts perfectly. Idles perfectly. Is nicely responsive to the throttle without any load. But as soon as I give it a little load either by setting the brakes and putting it in gear or by driving it, the engine will stumble and die or try to die when I give anything other than a very very careful, slow and steady acceleration.

Looking in the carb, there is plenty of spray from the accelerator pump down both throats. It's a nice atomized spray but there is a good amount. I can also see a good amount coming into the venturi when I flip the accelerator lever.

Is it possible the accelerator pump is flooding it out with too much?

What else might I look at with this carb?

I had no acceleration under load issues with the old carb and the only thing I did was change the carb..