on your bobbin case there is a very small screw that control the bobbin tension,turn clockwise and see if tension increase on thread,if not there could be some dirt stuck between tension spring and bobbin case body,use piece of paper to remove and try again
johan
January 2015
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix sewing machines.