• Too much oil in the bobbin and actual tension of the bobbin thread too strong
  • Dust or lint hards plug up the race surface of the hook
  •  Bobbin thread not neatly wound or thread tension of bobbin thread winder too strong
  • Needle not touching the extreme depth of the needle bar hole
  • Wrong threading
  •  Wrong timing of the hook
  • Lint hards plugging up the needle hole of needle plate
  • Needle and the point of the hook are bruised      
     Check All the above points and set your juki machine. This will solve your problem. Still, if you have any question then please ask me. I will try my best to help you, Follow my youtube channel for more updates. It will help you a lot. You will get my support related to your juki machines.