18aa367c_ooting_Sewing_Machine_Problems__Symptom
[Root Cause] Stitch length is too long for material. Needle point is blunt. Incorrect thread tension. Light pressure on presser foot. Fabric is too sheer or soft. Using two different sizes or kinds of thread. [Corrective Action] Decrease stitch length. Replace needle. Reset thread tension. Increase pressure on presser foot. Use underlay of tissue paper. Upper thread and bobbin thread should be the same size and kind. [Symptom] 
Fabric puckers.
Troubleshooting Sewing Machine Problems
Symptom