18aa367c_ooting_Sewing_Machine_Problems__Symptom
[Root Cause] Incorrect size needle. Improper threading. Loose upper thread tension. Pulling fabric. Light pressure on presser foot. Loose presser foot. Unevenly wound bobbin. [Corrective Action] Choose correct size needle for thread and fabric. Rethread machine. Tighten upper thread tension. Do not pull fabric; guide it gently. Increase pressure on presser foot. Reset presser foot. Rewind bobbin. [Symptom] 
Irregular stitches.
Troubleshooting Sewing Machine Problems
Symptom