'70 318 BBD falls flat under load

My 69 Dart ran like that for years, thru many carburetors, even a new long block. Turned out it was the carb and ran great with no stumble with the 4th carb. I think all the others idled too lean. I always wondered why I couldn't turn the idle screw to get too rich. That was a 225 w/ 1 bbl, but same concept. Indeed, I have a Holley Pro-jection TBI w/ O2 sensor on my Newport. If idling lean (LED indicator), it will stumble off the line. The accelerator pump (or function) worked in all these carbs (and TBI). If you install a rich/lean indicator (Holley or MSD), you would see what is going on.