First thing you will want to do is remove the spool of thread as well as the bobbin case from the machine. Next, using a long screwdriver, loosen the screw on the motor bracket as shown in the photos below:
With the belt on the motor pulley and the handwheel, depress the foot controller to full power and raise and lower the motor until the needle is going up and down at full speed.
Then while the motor is still running at full speed, tighten down the screw that holds the motor onto the motor bracket.
The belt is meant to be as loose as possible without slipping on either the motor pulley or the handwheel. So, if you find that while sewing with the resistance of fabric, the belt is slipping on either the motor pulley or the handwheel, you may have to loosen the motor bracket screw again. Move the motor down just a little bit to add slightly more tension on the belt until there is no more slipping, even while sewing with actual fabric.
If, after adjusting your belt, you find that it still will not hold a good rotation or is otherwise falling apart, then new belts can be purchased below. If you have further questions, contact us anytime.