When I had this issue.. it was because the tension was not right. I never touched the tension on the machine at all, but I had to wind the bobbins differently. The little tension thingy on top of your machine, wind the thread around that two or three times, before you wind your bobbin. Wow was I amazed at the difference in how my embroidery looks. Even designs I thought looked excellent... look even better. I also noticed by how many stiches I can get out of a bobbin now compared to before. I was having to change bobbins so much before..but not now. The bobbins hold much more thread now. Here are the same exact design.. the only thing I did different between the two was the bobbin winding.