I have 30 over 340 with eddy aluminum heads, 3310 Holley vacuum secondary, mild purple shaft cam good to maybe 5000 rpm, a built 727 tranny with 2500 stall, MSD mechcanical dist, E3 plugs, MSD 8 mm wires. It idles fine. At 3200 rpm the engine as developed a bang or mist fire. Oh, I did change...