Thread breaking can be from the needle in wrong, burrs on the throat plate, tension too tight, dried up oil on a thread guide or in the tension, thread wrapped around the spool holder or thread not through the thread guides correctly. Some times with the old machines it is simplest just to rebuild the tension once in a while. I prefer my 15 clone for FM but it is possible it is the foot I like. I've tried it with different feet and am happy with a certain one. Some times you just need the magic of the right machine and the right foot. Try normal thread in the bobbin and fancy in the top do your tension adjusting before you start FM.