As I try to sew, the regulator lever moves with the hand dial, and the stitch length changes. Any ideas how to fix it?
I think it is best if you download the service manual for your machine. Here is a PDF manual you can download. In the manual it shows you about this and how to adjust it. Here is your link.
parts.singerco.com/
There is also a video on YouTube that might help you with this problem.
www.youtube.com/
Some repairs appear easy but doing them from a manual or even a video is not always so easy.
If you feel you still need help you can always ask your question (free) at this link and perhaps they will have further instructions.