There are two different spindle drives that were used with this machine. A Contraves and a KTK (newer). I believe that both are 3 phase devices. If they were not, you could run the two good legs to these drives. None of these have a parameter list resident in the drive or control that is accessible. The control says go to such a speed and they comply. There are pots (adjustable potentiometers) on these spindle drives. If you have the book, it may be possible to decrease the ramp angle for accel and decel that way. Too much and the control will time out (parameter change).
You may want to check the brushes on the spindle motor while you are playing with the machine. They do have a tendency to wear out. Make sure the phasing is such that the spindle motor cooling fan is not working against the natural chimney effect.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)