If it sews and has tension issues' like needing a TON of upper tension it is probable that the needle bar and timing were 'adjusted" for the 15 series needles. Get you some correct needles and i will try to find my service mans manual. I reset everything on mine, not difficult, slightly confusingand time consuming, but not difficult... and I can try to help you out when I get back. Mine is working on all of the fancy stitches I have and I think I got it all right ;-)