I have never ever had problems with this machine so I got a rude awakening when I came unstuck with some very lightweight jersey for a top. No matter what I couldn't get the stitching right, using the same layers I would be stitching, until I finally got the book out and realised I was going the wrong way with the pressure button.
That sorted the stitching was perfect apart from tunnelling, which I've never had before. I read a suggestion that loosening the looper would help, which it did on the sample fabric but on the actual fabric it didn't and I still got tunnelling, although better. Another suggestion was to make sure that you are are not hitting just one layer, which I could be, second row just outside the double width. I've looked at another lightweight top and the stitching has landed right on the double layer edge so fine.
I'm hope this will work but if not what else can I do. I'm running out of spare fabric.