Kenwood Chef A901 rough operation at low speed?

I was recently given a KC A901 which worked, but seemed to start very fast and stopped getting faster after speed 5 on the dial. After a couple of uses it went pop and emitted smoke. I replaced the scorched capacitors and 56ohm 2w resistor. All worked again but the speed dial problem remained. Your thread below has been massively helpful and I have found the speed control screws and adjusted them. I am now getting a full range of adjustment on the dial and around 60rpm at low speed, but the machine sounds really rough at anything up to about speed 4 with a lumpy uneven sound and vibration. Can anyone advise? I also wondered if the 2 screws need to be adjusted to the same distance? Also, can anyone advise on the correct rpm at maximum speed? Can adjustment of the control screws make the machine go too fast, or will it only go as fast as it should?