1 Armature/springs too much tension
Rear spring could be bent too much, loosen the back spring screw, flip the back spring/armature bar/front spring assembly around and turn it around so that the front spring is facing downward on the other side of the frame (basically you did a 180 with the assembly).
2 Too much voltage
If you need to run the machine at max voltage or near max, there is something wrong with the way you tuned. You’re going to need to adjust the tensions on the springs or gap of the front spring to the contact screw to lower the amount of voltage necessary to get it to run right.
3 Needles set inappropriately
Keep the needles slide vertically into the tube, grip, touch nothing. With the constant vibration of tattooing, nipples and rubber bands may become loose during use. Adjust the connection to make sure needles set appropriately.