Originally Posted by
trivia42
Tension would be the first thing I would check, both bobbin and top. After that I would make sure the timing is good, if you're hitting the bobbin case with your needle instead of going through the hole in the case you may need to have it looked at.
I just had this problem. I rethreaded the machine, checked the bobbin, neither worked, then I remembered I had adjusted the tension recently. Readjusted it one number at a time, was able to keep a beautiful even stitch while totalling eliminating the bird nest problem. Of course, I had thought the machine would need to go in for service, and every other wretched scenario my tortured brain could conjure, including multiple $$. It was such a simple fix and she is humming away once again.