Pfaff varimatic 6091 sew a rag quilt with jean and flannel,I can't get my tension right it seems to be funny on the bottom stitch,where shoulf the top tension be set at 4 1/2 ,when do I adjust the bobbin tension?

Hi! The bobbin tension rarely needs to be adjusted. First, make sure you're using the appropriate size needle and thread for your fabric (I'd probably use either a 'denim' needle or a universal size 14) and also that the upper thread and bobbin are threaded absolutely correctly. These can throw off the tension! Also, take the time to clean out the bobbin area. That can throw your stitch off also.

If the stitch on the bottom is loose, so that you see the top threads, then the top tension is too loose. If the top stitch is too loose and you see the bobbin threads on top, then the top tension is too tight.

It helps to thread the machine with different color thread on top and in the bobbin, and then stitch an inch or so on the same type of fabric as you're using in your quilt. Check the stitch. If you need to adjust the top tension, make sure the pressure foot is down! Adjust a little, stitch a few inches, and check again. Repeat until you don't see any (or very little) bobbin thread on the top or top thread on the bottom.

If you go through all these steps, and the bobbin thread is still loose (and you've tightened up the top tension), then there is a tiny little screw on the side of the bobbin case that you can use to adjust the bobbin tension. Turn the screw just a little bit (less than a quarter turn), stitch, check, etc. Once the bobbin tension is set, you shouldn't ever have to change it.

Let me know if this helps, ok?

Happy sewing!