Great machine, except that I have found that, although it is advertised as a machine that will sew fast, if you actually do sew fast (and I'm not talking about anything unreasonable here), it will jam up.  I took it apart to see if I could figure out what was going on and I found a thin wire hook that looked to be a thread holder of some sort.  I'm wondering if sewing fast makes the thread jump off that hook---not hard to picture.  Really good machine in every other way and I try to remember to take it easy.