Originally Posted by
Rach L.
I'm afraid to mess with the screw too much, so thought I'd ask before I really mess something up. In addition, when I sew, it's obvious the tension is off somewhere, though I can't tell where the problem lies (this was happening before I turned the screw on the bobbin case, which is why I figured I had nothing to lose).
OK, we're nearly there, you need to mess with the screw. I'm guessing that because your zig-zag stitch is pulling the fabric together with the upper tension loose, the bobbin tension is still too tight.
To test, hold the end of the thread, suspending the bobbin + case. Properly adjusted, it should be at the point of falling and will do so if you gently pull upwards. It should be adjusted until you reach the point of it falling by itself.
When this is set, you shouldn't need to adjust the bobbin tension again.