I am having two problems or two symptoms of the same problem. I just rebuilt my first engine - 351W. Comp Cam XE274H (specs here), AFR 185cc heads, Holley 650cfm Street Avenger (vac secondary). The engine starts easily, but runs rough. It idles at 1700 when choked. However, I cannot lower the curb idle once the engine warms up. The curb idle screw is backed completely off the throttle linkage but the car still idles at 1200rpm. The throttle seems to have full travel without binding. Fuel level is set just below the sight windows. Fuel pressure is 5. I have tried to adjust the fuel mix screws, but it doesn't seem to make much difference so I set them at 1.5 turns out. I have tried adjusting the secondaries to have a "square transfer circuit" (basically just a pinhole size). It still idles fast, even when warm. Secondly, the engine runs a little rough at idle. The vacuum is reading approx 15 but rapidly "flutters" between 14-16. If I increase the throttle, the engine is smooth, but at idle, it is rough. I got this carb new from Summit, but I think it is a "returned item". The literature that came with the carb says that it is set from the factory, but when I got it, one idle mix screw was out 1/2 turn and the other was out 2 turns. The transfer circuit was open about 1/4 inch. I've studied various places on the net looking for answers, but haven't found any yet. My next step is to confirm no air leaks. I don't have anything connected to the carb except the vacuum gauge (no brake booster, vac advance from dist is plugged, no PCV). Gonna do the carb cleaner spray trick. Any other ideas from you carb guru's? I am hoping both of these symptoms are from the same problem rather than two separate issues. If I can't find an air leak, I'll pull the plugs and check them, but they are new with less than 30 minutes total run time.