Question on Carter AVS Carb 4618????

Note sure of the screw thing yet. I did try the old hot rodder trip, and put the 440 carb on the 340. The original 340 auto carb worked better. The car slowed down 1.5 mph in 1/4 and 4 to 5 thents. I guess I will stick with the stock smaller 625 cfm, instead of the 440 carb 725 cfm.