Black smoke is usually indicative of running rich. You have no other mods, other than what's listed? If you have n FPR, you can try backing your fuel pressure off a little. Other than that, check your plugs and see if they're black, and make sure the rest of your ignition system is in good working order. Check the distributer cap and rotor, plug wires, etc. If your ignition isn't completely burning the mixture in the combustion chamber, that'd explain the rich condition.