Hello everyone,Blown Burb here. After still checking and testing just about everything we could think of on my sons 454, I tried adding a couple of small washers to the accelerator arm spring. Another change was the accelerator pump sprayer nozzle hold down screw I have removed and drilled out on a drill press so that it was close to the described Holley part no. 26-12 screw for the nozzle. Im happy to say that either off the line or at various low speeds now there is no more stumble. I suppose its needless to say that the rear tires just can't seem to stay stuck to the pavement. I'm sure there is a stiffer spring available and the jump from the original sprayer nozzle from 25 to35 was only the begining. My son and I will still have to set up the main jets, because even after dropping down from the stock no. 72 jets that the carb. came with, its still running rich. Currently the main jets are no. 68, any suggestions on what may be the smallest jets to go down too with this carb. size before running too lean from past tries with this previously mentioned setup. Well bye for now and I will post any new developments.