I have a 1600P & the tension is tricky because (on mine anyway) doesn't have markings & the dial can keep spinning. I took it in to get the tension set correctly & the best way I can describe it to you is the little line needs to point at the 4 o'clock position. Try changing your needle to a 14 or topstitch needle & make sure you get in the last thread guide by the needle. Someone on here suggested only looping through one of the top holes before the tension discs. Hope this helps.