Originally Posted by
labeelady
I recently went to a demo on the Bernette Deco 340. The Bernina rep said the same thing about using pre-wound bobbins! She said the machine winds them at the right tension. The pre-wound bobbins may or may not be wound correctly. In fact, she told me that if you take your machine to be serviced and they find out you're using pre-wound bobbins, they may void the warranty!
This may be the most correct answer, assuming she was talking about the bobbin. I even had a bobbin wind incorrectly on the machine I was using it on; I didn't pay attention when the thread slipped out of the guides so it wound really sloppy. This was in a class and the instructor caught it before I did. She made a similar comment. I also tried winding bobbin thread for my Brother embroidery machine on my regular Brother sewing machine and that didn't work well. Same bobbin, same winding method, different tensions for the different machines.
There is undoubtedly nothing wrong with the thread itself, but your bobbin may not be wound correctly for your machine.