I found that if you've tried everything else, rethread, new needle etc, and the bobbin thread is peaking through on the top, you can tighten the bobbin case just a tad and see if that works. I have an Esante ese2 and it is a pain to set up for free motion. I can't take the stitch length down to 0, and it was never right . I did go to the zig-zag, took it down to 0 and length to 0 and it works better. go figure