I rarely have trouble with bobbin tension on my Handi Quilter Sweet Sixteen (I use Jamie Wallen’s method here: https://www.youtube.com/watch?v=Q1mRhcquZTM), but it was playing up a bit this morning. I was still getting good stitch formation, but found I was having to keep loosening the top tension. I checked the bobbin case and it was threaded correctly, but it was a bit too loose. I initially tightened the bobbin case screw, but then I noticed something—the outer tension ‘spring’ didn’t seem to be sitting flat and locked in.
I’d cleaned it out with a business card when I finished quilting yesterday (one of the things I do when I clean and oil the machine at the end of the day). On closer inspection, with my magnifying glasses on, I saw that the bottom ‘hook’ bit wasn’t quite in properly (see where the red arrow is pointing in the photo below). I gently pushed it with a small screwdriver and it snapped into place.
Bobbin tension issue solved!
Rhonda Bracey: At Random 
such simple stuff!!!! and I would not have looked at that! will now