Sometimes the more we fiddle w/tension, the worse it gets. A tiny adjustment makes a world of difference, so try not to create new problems for yourself by going crazy with adjustments. It is a slow process, but if your tension is off - try this...
- put in a NEW needle before you begin
- get out a piece of light colored muslin and fold in half (or use 2 pieces of fabric together)
- thread machine w/ black on top and white in bobbin (this will make it easier to identify which tension needs adjusting)
- using roughly 8-10 stitches to inch (not too small and not basting), stitch a 6-8" line on your piece of fabric
- examine the stitching to find out if it is your upper or lower tension which needs adjustment => do you see looping or snagging on either top or bottom line of thread?
- make small tension adjustments (top tension dial and bobbin case screw) and keep repeating this process until you have a line of stitching which looks even and roughly the same on both sides of your fabric
next step - fine tuning
- make a line of stitching 8-10" ACROSS THE BIAS of your double layer of fabric, back stitching at each end to lock
- pinch both ends of this line and gently pull until your thread breaks
- if your thread breaks on BOTH sides at the same time, your tension is perfect
- if your thread breaks first on top, loosen top tension by make a "tiny" turn of top dial; if it breaks first on the bottom, make a "tiny" bottom tension adjustment to casing screw
- [i]please NOTE there should be a little give on a bias line of stitching before thread breaks, otherwise seams you make on curves (crotch & armhole) will keep ripping out on you[/i]