You seem to have 220 volts AC at the outlet. You stated that you do have a variable speed controller. There are both AC and DC controllers and motors. If your motor needs DC current the control box does the conversion for you. Some of these motor / controller combinations don't have a lot of power at very low rpms. If you move your belt so it is on the smallest motor pulley and the largest lathe pulley it should help the situation. You can then run the motor at higher rpms and still get the low rpms on the lathe. I have an older nova 3000 with a dc variable speed motor. To get power at very low rpms I have to use the low pulley setting. Can you ask the person you bought the lathe from how it worked for him? Also the DC motor / controller combinations tend to hum at low rpms.
Tom