I had this very same problem with my Sapphire 870 that I bought on Ebay. I was always having to adjust the tension setting before I could sew. Took it into Viking dealer/repair person for a different problem, and they gave it a complete overhall or tuning. Since then I have had no problems with tension. It is set at the 4.6 and sews beautifully now. Maybe you should just get a tune up.