I was having problems earlier this week and realized my bobbin was too full. I usually always stop the bobbin winder before it is completely full, but this time I let it run till it shut itself off. When the bobbin is too full, I have problems. Also, are you using the same thread in the bobbin and the top of the machine? Are you using a "different" fabric, like a flannel or fleece? Do you have your feed dogs up or down? Remove the plate that the feed dogs stick through - you would be surprised all the lint that collects there. Then re-thread the entire machine. Good luck.