could be simple matter as wrong needle.wrong threading,wrong tension or little more complicated hook timing is out,to check make sure needle is inserted correctly that means back of needle against hook and then check if timing is correct by turning handwheel and observe if hook point is approx 2mm above needle eye when needle is moving upwards
johan
November 2014
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.