I have a 6500. I have found that I can use any thread, as long as the top and Bobbin thread are the SAME. Also, only use Janome bobbins. The other brands seem to be just a hair off in size. Once I stopped using them, I had no problems at all. If you purchased the machine used, check your bobbin case. It may be cracked or just worn on the edges of the plastic. A very inexpensive item to replace.