I purchased a used Viking 960 a few months ago and it came with the instructions manual, but I am having a problem I don't know what to do about. I have noticed that whenever I sew very fast, the tension thread on the bobbin knots up. I think I have threaded it correctly on top and bottom (bobbin), and have even re-wound the bobbin thread. The machine sews beautifully as long as I amble along at a leisurely pace, but when I speed up I run into problems. I have adjusted both tension settings and that is all I know to do. Anyone out there have any suggestions for this machine? I was loving it but am getting very discouraged, and this, along with my being new to quilting is about to bring me to a screeching halt. BTW, I ran into the problem when I was joining a regular piece of cotton calico cloth, probably 200 TC (not thick at all). Thanks in advance for any help from anyone.