if you move the handwheel is the feeddog moving and if you adjust the stitch lenght is the stroke changing.is the feeddog set for feeding or set down for freehand working.if you answer no to any off these it could be a loose conection between feeddog and main shaft.only way is to open up and see where problem is ,that means dry parts or broken/loose connection
johan
July 2012
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.