I was having that issue on my Viking Designer 1 too. So I adjusted the little screw in the bobbin case .....tighened it. Have had this machine since 2000 and never even thought to do that till I got a quilt machine where you're always changing the tension for the various threads you use. Learn something new everyday. Seemed to help my situation. It doesn't take much of a adjustment on the little screw in the bobbin case either.