feed dog need to be adjusted,could also be a lack of oil on feed control,not so easy to explain how to set but if you techno minded you can try this.open bottom panel to gain access to feed dog control and see if there is free movement if feeddog is moved back and fro by hand,now you need to find the cam that control the stitch lenght and adjust by loosening and turn cam until more feed is obtained.be carefull and sistematic and you may just get it ,if not it is a quick job for a techno that knows its stuff
johan
May 2014