Carter BBD

I have a summit/holley reman on my car 73 scamp. summit part number 64-1169. The engine itself is a 1970 318 out of a dart. My problem is the tendency for the car to stumble when giving gas too early. I have to be real gentle with the car. What it does if i give it to much gas is stumble, sometimes a slight pop, then it limps up to speed. I drove it from my house to breakfast, about 1.5 miles. I let it warm up for 30 seconds in the driveway at 1500. When i got to breakfast, the choke was about 75% fully opened. I beleive the stumble is a lean condition. But, i have the "pfft" "pfft" "pfft" sound of a rich running car. I have been slowly leaning out the idle mixture screws which is reducing the frequency of the "pfft" "pfft" "pfft" sounds from the tailpipe, but i think its cause my lean condition. Putting the old bbd back on is out of the question, because i could turn the mixture screws all the way in, and it would still be slightly rich. And the floats liked to randomly stick in it