It's easy to set the tension. Adjusting the tension nob on the machine doesn't help then it might be time to have a look at the bobbin's tension. on the bobbin there is a little screw where you can tighten or loosen the tension. The tension must not be too tight or too loose. It must be, when you pull the thread, sort of bouncing. UMmm difficult to explain. if you pull the thread it must give a little then stop, when you pull it again it must give a little and then stop.