Hello Eye,
It will be a tension problem, remember that Singer machines are best used with a mercerised no thicker than a number 40, top tension should be about 4 or 5, you should only just be able to pull the bottom thread through with some slight resistence, if it is too tight slacken the screw on the bobbin case about a quarter of a turn anti clockwise and test sew, keep adjusting until you get it right.
Try www.sewing-machine-manuals.com for instruction books or www.sewingonline.co.uk
Ken
drivewithken, September 2009
