If you’ve twiddle all the relevant dials, changed your thread, changed your needle and still your machine stitches or tension is loopy or tight or just not looking ‘right’.  Then the next step is check your bobbin…

Is the bobbin the one that came with the machine? Don’t presume that all bobbins fit any machine – they definitely don’t , even the ‘universal’ ones.  A very tiny difference in size or shape can mess up your machine’s tension and quality of stitching.  Take a look at the bobbin side on – see photo – some are slightly wider or have a domed shape.  Test which works best and chuck the others away.

ALSO the thread should be wound evenly on your bobbin not ‘cone’ shaped like the one  on the left.