I've been running the 750 cfm vac. secondary on my 351W w/ Edelbrock RPM heads, intake, Comp Cams 280H cam, headers, etc. I could not get rid of the off idle stumble with this setup by adjusting the carb. I even bought the tuning kit and changed metering rods, springs, etc. My best et. at the track was [email protected] mph with me babying it off the line to get by the stumble. I finally got fed up, called Edelbrock tech and they said the accelerator pump circut is too weak, wanted me to drill out the shooters to help get rid of the lean condition when I launch. I decided instead that I'm going to sell the carb on and switch to The Speed Demon, 750cfm, mech. secondary. I went to the track today after just literally bolting this new carb on and ran a 12.89, 12.93 and 12.91 right in a row, most consistent 3 runs I've ever done and absolutely NO stumble, bog or hesitiation. Anyone badmouthing the Demon carbs can try my Edelbrock. The throttle response is like night and day and my idle even smoothed out compared to the 1407. I'm overall very impressed and this is the best my car has ever run. I noticed my plugs were a little dark so after re-jetting I think it will do even better which is impressive for a 3500lb car.