When I had a Bernina, I had to change the bobbin tension for FM quilting. I kept one bobbin case just for that. (My Janome has a separate bobbin case type designated for FM also.) Having your bobbin thread NOT on top for starting makes a differnce too. Sometimes lint can cause this problem. It can hide in all sorts of places. Poor dealer help was only one of my Bernina problems. My Janome dealer will talk me through things like this over the phone!