I recently had the same problem. My true friend Elna SU (1972) was severely misbehaving. I was confused because I bought her brand new that many years ago, and never had a problem.
Frustrated, I thought, well, no machine will last forever. With fear and panic I shopped online for two days trying to get caught up on technology. After reading many articles and reviews, and still confused about how to decide on what I could afford. I thought I better do a thorough examination.
So, took everything apart, thoroughly inspecting and methodically checking every adjustment and installing new needle - I held my breath and started testing every stitch. Guess what! I ended up with a perfect sample of all stitches and variations! Somehow I knew back then I had bought the perfect machine - told my husband I should have bought two at the time, and saved one!
I'm so glad we're both happy! Have fun - I know I will!