hawker has the method of adjustment right. Depending on the motor, you may have a gradient on the can and a line on the endbell or a line on the can and a series of notches on the endbell. Most motors have the later marking. The middle notch on the endbell is zero degrees timing and may have a slightly different shaped notch. That's what you use when you're breaking in brushes or if you want to sandbag your speed during practice. Each notch on the endbell is 12 degrees of timing. You always rotate the endbell counterclockwise to add positive timing. Never add negative timing. If, for some reason, you are running your motor in reverse polarity, you would do the opposite of this. More timing equals more speed and much more comm wear. I would not go beyond 36 degrees of timing or performance will suffer. It's actually around 40 degrees, but you don't have a very accurate gradient. If the can has degree markings on it, it should be pretty self explanitory. Just make sure to add positive timing only. See, if you raced stock, you wouldn't have to worry about all this!
