Test sew with two layers of woven cotton fabric. Make sure the needle is in the correct way, and use a new sharp point needle. Worn needle tip can cause hickups.
Check the top tensioner; it should turn smoothly from about 0 to 9, or even 0 to 0. It doesn't matter if it's a bit off the mark, as long as it turns freely all the way around. Use regular sew all weight thread, mercerized cotton or Gütermann sew-all polyester is good for tension adjustment. Set the top tension between 4 and 5 and fine tune bobbin tension from there. Use a good quality thread, a known brand like Gütermann (or another trusted brand) is a good choice, it will give less factors to worry about for test sewing purposes.
Check the thread you are using, it should not snap between your fingers too easily. What type of thread are you using.
The hand wheel can be turned backwards to lift the needle, but more than that and will mess up the thread. If the thread catches or tangle, it will make the hand wheel stiff and when forced, the thread will break. Generally; the hand wheel only goes in the direction the motor runs it.
Another thing is to make sure you match thread and needle size suitably for each other as well as the fabric. It can make all the difference for heavier or densely woven fabrics.
Clean and oil everything, make sure the tension disks are clean as well as the tension spring on the bobbin case.
Last edited by Mickey2; 03-12-2019 at 12:33 PM.