Well, this is a very contravercial subject, but from my research, I have found this.

Here is what you do.

With the engine in the car, Run the motor as slowly as you can and very rich, for about 2 minutes, then let the engine cool completely, then run it as slow as possible for another 2 minutes then let it cool completely, continue this for about 3 tanks. REMEMBER that when your motor stops to cool, make sure the piston is at the bottom of the stroke. Once you have completed this, then start to cycle the engine in the 2 minutes by taking the revs slowly to about a 1/4 throttle, then down, let it cool again, do this twice, then take it to half throttle and down, but remember to be progressive, smoothly up, and smoothly down. Let it cool, do this twice, then to 3/4 throttle and down, do this twice, you are now ready to start to lean it out and get it up to race tuning. Remember to change your plug when you have finished.