I have this machine also and am just starting to try and use it for leather.
I picked up a small test bundle of 207 thread and some 135x17, size 24 needles. I don't know how to tell if they are Leather needles or not. labeled SY3355 and DPx17
I loaded some of the thread onto a bobbin, put it in, and tried a number if upper tensios but got shaft lockouts, jams, and all sorts of issues.
Am I trying to use too large a thread with this machine, or did I use too large a needle? I was trying to sew through a piece of slightly under 1/4" veg-tan with a thin piece of upholstery leather glued to the back.
Thanks
Tom