I have a new GM performance 350 crate engine, Vortec heads, dual-plane intake, Holley 670 vacuum secondary carb, mild cam and HEI ignition. All came as a complete engine. 9.0:1 compression, and cam specs are 215°/223° at .050 .473" lift with a 108° LSA. I have timing at 10° BTDC and idle mixture screws 3+ turns out balanced. If I adjust mixture screws in to say 1 1/2 turns engine will not idle well especially when in gear. Also smells really rich when backing in garage. I also have a problem with the engine running on after shutting down. I shut down in gear to avoid.