Pfaff has been manufacturing sewing machines since 1862. Their line includes industrial, home, embroidery and speciality sewing machines. Many Pfaff sewing machine issues can be directly traced to thread tension problems. To sew correctly, the thread tension needs to be balanced between the top tension guides and the bottom bobbin feed. Signs of incorrect tension include stitching loops on the top or bottom of the fabric and problems with the cotton breaking. There are many different models of Pfaff sewing machines, but the basics of adjusting the thread tension remain the same for all of them.
Remove the existing thread from the top guides and the needle. Remove the bobbin.
Thread the sewing machine from the beginning, using your manual as a guide to ensure that you follow the correct threading path for your particular Pfaff. Turn the top tension guide to the middle position.
Place the bobbin in position. Check that the exiting thread goes into the slot in the bobbin casing and stays behind the thin bobbin casing pressure plate.
Turn the Pfaff sewing machine wheel by hand, just enough to pull up the bobbin thread through the sewing machine pressure plate.
Insert a piece of scrap fabric, lower the pressure foot, and stitch a short line. Remove the fabric. If there are loops on the top side of the fabric, the problem is probably with the bobbin tension. If there are loops on the bottom side of the fabric, the problem is probably with the top thread tension.
Lower the pressure foot and gently pull the loose end of the top thread. There should be a slight resistance. If the thread is hard to pull, loosen the upper tension until the thread pulls easily, but with a slight resistance. If the thread pulls very easily with little to no resistance, tighten the upper thread tension until there is a slight resistance.
Pull the loose end of the bobbin thread gently. There should be a slight resistance. If the thread is hard to pull, turn the bobbin tension screw an eighth-turn counter-clockwise. If the bobbin thread pulls too easily, turn the bobbin tension screw an eighth-turn clockwise. Keep turning the screw, an eighth-turn at a time, until there is a slight tension on the thread.
Sew another stitch line on the scrap fabric and check the stitching. If there are still thread loops, continue tightening the tension on your Pfaff. Tighten the top tension for loops on the bottom of the fabric, and tighten the bobbin tension for loops on the top side of the fabric.
If your Pfaff sewing machine model has two bobbin screws, turn only the screw closest to the spring. Always adjust the tension a little at a time. It is easy to go from "too loose" to "too tight."
When adjusting sewing machine tension, always start a stitch line by turning the wheel by hand before letting the power take over. This will help prevent broken needles and jammed feed dogs if you have the tension too tight.