Yellow,
I'm having the same problem with an Eagle copy of your machine. I recently picked it up and after a thorough cleaning and readjustments to get it sewing I had a good 5 stitches per inch but no reverse. when I balanced the reverse I was left with numbers similar to yours. I haven't yet figured out if my particular machine is just not capable or if something is out of adjustment. I've contemplated setting a 50% reverse imbalance so I can get a longer stitch length but still have a relatively neat reverse pattern.
One thing I've been curious is if my handwheel is rotating enough. Are you able to measure or at least estimate how much the wheel rotates from min stitch length to max? I'll try to measure mine tonight and report back.
This is the video I used to do my adjustments. (thanks Uwe)
