[Espeefan]

Thor, if you look closely at a motor end bell, especially where the brushes lay on the commutator, you'll see the commutator is divided into segments. Each segment of the comm is soldered to the wires of an individual motor winding. In other words, each segment energizes a single winding, creating a magnetic field. The windings wrap around what we call an armature. The magnets inside the can of the motor are naturally attract the windings, which pulls the armature, as they are energized, and this makes the motor shaft spin.

There is a important relationship between the timing of an energized motor winding, and the magnet. The point at which the winding is energized, as it spins into the magnet's natural field of pull. The engerization of each winding needs to be timed so that the power to the winding is shut off slightly before, or right as, the winding centers itself above the magnet's field. If the power was kept on after the magentic fields center themselves, the motor would stop spinning, or at least slow down because the attraction would try to brake or reverse the rotation. Now depending when you energize the winding, you can make the magentic attraction start happening sooner, or later. This is where the motor timing comes into play. By advancing the timing, you are engergizing the windings sooner, and also shutting them off sooner. It's all in relation to the phasing of when the magentic fields attract to one another. Sooner gives you a little more torque and RPM, but only in one direction of motor rotation. If you run the motor in reverse, it's timing is now off slightly, hence it runs slower.

Think of it like advancing the distributor on a car (that has one anyway!). It's the same effect. You increase the point at which the spark fires in relation to the piston making top dead center. You can pick up a little power with the right adjustment.