I had this problem last week with my Tin Lizzie, didn't matter what thread I used. The dealer talked me into buying King Tut (sooo expensive) but didn't solve anything. Then I realized I was using a thinner batting and thought to let the foot down a fraction more - it worked! Haven't had a broken thread since. By the way, I'm quilting with machine embroidery thread on top for this quilt and all is well.