Swapped carbs, big improvement

[tdangle]

I installed a deluxe GM performance crate engine (SP350/357 HP) earlier this year. It came pretty much complete, as far as fuel and ignition. 670 Holley carb sweet avenger with vac secondaries and HEI with a GM dual plane manifold. I have a 2 1/2" dual exhaust with stock exhaust manifolds. TH2004r trans stock converter and 4.10 gears. To me it seems like it's never run quite. Loads of power, but drivability lacked. Very uneven idle, Lugs at low RPM's really bad. I have tried tuning the carb, have had it dyne tuned still not all that great. Just swiped the carb with one a friend had laying around. 750 Holley classic style with vac sec. So far it is a 100% improvement. Seems to be a much better idle with mixture screws out 2 turns. with the 670 I had them (and the dyno tune was the same) 3 1/2 turns out. very smelly exhaust backing in the garage. Now its much better. I will need to give the carb back and am thinking of EFI since I now know it was the new carb that came with the engine that made it run crappy.