How do your stitches look back and front? When you put your bobbin into the holder the thread shoukd be going in the opposite direction of the "tension hole". When I got my last one it was threaded all wrong and once I re-threaded it has been fine ever since, My upper tension on all 4 machines is
set between 3-4 using superior or aurafil thread. I use superfine pre-wound bobbins in the bottom. Hope this helps.