Turn you upper tension to 0 and turn it up 1/2 until the stitches are sewing like they are suppose to. I have to set my tension to 1 to get good stitches. If you have a bobbin winder that has a knob or lever to push to wind the bobbin be sure it is disengaged all the way. Even a fraction engaged will cause havoc with stitches. Also be double sure you are threading through the tension properly. Check your manual pictures even though you know it by heart. A few days ago my FMQ was going super for a few hours and then the thread started breaking. Never did figure that out. I just changed to another machine to finish up. I don't spend time fussing with a problem I go to my back up machine and let the problem work itself out. Usually by the time I get back to the problem machine it works fine again.