i would recommend visiting the web site and seeing if you can download a maintenance owners manual---i managed to get one free for my vintage singer- it sure helps to have the diagrams right in front of me-with all the screw locations ect-right next to me.
tension is such a (fickle) thing- it would be best to have the manual- or if you have a local repair shop that works on vintage machines they may be able to help-
good luck