If you haven't, due to it's age, I would suggest opening it up, cleaning it with a machine brush (they are small) and doing an oil job with machine oil. I wouldn't suggest using the longest stitch length, as that is what you use for "basting stitches" and it doesn't hold well.
You may want to play with the tension as well.
A good idea is to take scraps of fabric and sew, adjusting the dials as you go. Look at the fabric carefully and note where it gets good :-)