confused everytime i drive at w.o.t. the car leaves a cloud of black smoke from the starting point. it then goes away as i hold the pedal to the floor. also between shifts the car lets out a puff of black smoke. the engine runs smooth and does not lack any power. the car is tuned up (has new plugs, cap,rotor,fuel filter). i have headers an exhaust and a cold air intake. any thoughts?