My Shelby clone is running a 715 Lemans Carb. After a year of tuning, the engine idles smooth as silk at 750 RPM, pulls hard with no flat spots and starts the second you hit the key. The only issue is left is that I am still running rich with black soot on the plugs and out the exhaust. The primary jets are stock 68s with 78s in the rear. Should I try 66s in the primary side or just leave well enough alone?