This might sound strange, but make sure the bobbin is right side up and wound right side up. My bobbins are marked so I know top and bottom (and even then I have done them upside down). A bobbin wound wrong or in wrong can do that. When you thread your machine, some spools pull with the thread to the front, some from the back or over/under. The thread for the bobbin then would have to be wound with the thread coming off the spool in the same direction. Look in your book and see what direction the thread come off the spool and thread accordingly. If one or the other is not wound in the correct direction, you get a backlash..........
Hope that helps, or you can understand what I mean.
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