Originally Posted by ckcowl
if you are getting loops on the back your top tension is too loose, tighten it a little at a time do a practice line of stitching and continue to adjust until your tension is equal top and bottom. it is very easy to adjust your bobbin tension also, next time you take it in for service you should ask the tech to show you how if you are not sure how.
Great advice, also, if you are doing a lot of twists and turns, it is hard for the tension to remain correct. I have a mid arm and if I do a lot of loops even with a stitch regulator (especially if I do them quickly) I can get some railroading on the back of the quilt.