And if all of the above fails to cure the problem................... I had trouble last fall with my longarm. I could stitch a straight line, never change the bobbin or top tension and would have sporadic bad stitching. If yours is doing this (meaning, if it's not when you just do loops), then get a new bobbin case!! I went thru a nightmare trying to figure it out. My old bobbin case had a piece that was supposed to be straight/flat. Mine tilted....the thread would go thru this area and was fine, then it would slip into the tight area and not be good, then back again. It was a bear to figure out! (meaning I cried a lotta tears!). Good luck!