I hope you got your tension worked out (keep testing - start with the bobbin, which might need a micro-adjustment). If your King Tut is on the spool, use a horizontal spool mount; that helped tremendously. My machine has same symptoms, which in the past was from a barb on the hook (was repaired but symptom recurred after a while). A technician told me this machine has a "tight clearance" for needle and thread. I can run 50 wt thread without breakage, but 40 wt results in shredding - but only in one particular direction when FMQ (no problems otherwise). Going to a different technician for 2nd opinion. If I need to replace the hook, it would be worth it. This machine has been trusty! Lately I've been running 50-60 wt thread in the bobbin and 50 wt on top. I can usually run 40 wt on top if I have 60 wt in the bobbin and keep the speed slow (and size 90/14 needle) and don't go "backwards" when FMQ. I tension test every time I change any variable.