welp i got a 283 chevy with a th 400 tranny all in a 1950 chevy pickup.... i just swapped the stock intake and carb with a holly contender intake manifold and the Holley 600cfm Vacuum Secondary Carb. i did all this last night in about 3-4 hrs... we got it runnin but it backfires like a mother and consistantly and it idles extremely high and we backed the idle screw all the way off. we didnt have a timing light so we just timed it by ear to get me back home with it. when i drove it, i didnt expect much at all but i had to play the throttle (in and out quite fast) just to get up to speed otherwise it would bogg out and die. also when i was driving it, it didnt backfire nearly as much. the main vaccum line on the carb we had hooked up but the other little one we didnt. i didnt mess with the fast idle screw or anything else cuz i dont know all that much about carburators. any help would be appreciated. ill keep you posted if i remember or fogot anything else... thanks alot ppls ...