I have used walking feet on a 99 and a 201, both cast iron straight stitch models. The feed dogs and presser feet are very similar to the 221 and I guess they are much the same. I like the Swiss zigzagger, I can adjust the stitch length on it to the same as the feed dogs with a bit of test sewing and comparison. I can't remember it mattered much with the newer one I had, it was not the new especially made for straight stitch machines available on the web (ebay, sew-classic,...) Some have had problems with the feed dogs not aligning up correctly with the newer walking feet. Zigzag machines have wider set feed dogs.
There should be gradual speed or something is wrong with the controller. The motor runs easier after cleaning and lubrication; the same for the rest of the machine. It's easier to get a nice, even stitch length on high speed, even movements, experience, developing a feel for it and all that...
The favorite for freemotion and quilting is a singer 15, and there are feed dog covers available for your 221; a smooth cardboard, plastic or something like that will work just as well. There are example of people doing wonderful work on 27s, 66s, and 201s as well, and I guess the tiny 221 is up to it.
Last edited by Mickey2; 08-30-2017 at 12:48 PM.