advancing the timing on a mod motor means turning it more in the direction of rotation. looking at the end bell, this means turning it clockwise. From say 12 deg to 32 deg. Last time I checked (I still may be wrong, need to check this out tonight) this meant more speed, less torque.
The same can be done with a fixed endbell by trimming the cut of the brush.
for how to cut a brush to increase the timing, what I call advance (and may be incorect)
This may also be a semantic issue, my definition of advanced timing might really be retarded timing.
Leading edge cuts = more speed
trailing edge cuts = more torque
advance, retard, whatever, the brush cut matters. If I read the other posts right, we are saying the same thing.