I have Edelbrocks on both my Chevelle SS w/468 BBC and on my 70 Nova w/350 and they act the exact same way. I have electric choke on both and have played with them extensively to try and correct this without success. I think is has to do with how Edelbrock does the choke so that it won't change position until you floor it if it is not open all the way. On both of mine I can floor it and it will take off right after the stumble, but then it overrides the choke and fully opens the plenum. I'm guessing at this, so if anyone has a better opinion or a way to cure this, Please let me know. FYI, I run O2 sensors in both cars to verify tuning once they are warmed up, so I know the cars are tuned good but it takes a while to warm the O2 sensor so it will work right. About the time the car is warmed up, the O2 sensor is warmed and working good...so it doesn't tell me what is happening when the engine is cold. I have also tried changing rods, jets, springs, pump position, A/F ratios, etc. and nothing seems to cure it. I would like to fix this, so if anyone can help, please do so!!