I use a Bernina 440E with the BSR foot, which I bought especially to fre motion quilt. I generally have thin cotton batting and either cotton or multi purpose thread. My frustration comes from the fact that sometimes it is perfect and sometimes the problem occurs with the top thread showing through. It may well be the speed of movement. I have used different needles and different threads and tension adjustment to try to find the root of the problem. Thanks for your suggestions.