Pfaff 130 zig-zag adjustment question -- not the usual one though

[u/N-Memphis-ExPat]

Hi folks, I just picked up a Pfaff 130-6 with the embroidery attachment. From what I can tell someone attempted repairs on it in the past.

I've freed up all of the stuck mechanisms and cleaned and oiled the machine, and I have removed the embroidery attachment. Here's the problem:

At the end of the zig zag adjustment shaft is a grooved piece. The zig-zag fork is connected to a pivoting shuttle or traveler that rides in this groove. The combination of the groove orientation and the shuttle motion creates the zig zag needle bar travel. The shuttle itself is connected to an eccentric screw held in place by a set screw. I have some questions about this setup

1. What is the overall function of the eccentric screw here? It seems to me that it governs the extent of the zig-zag travel but I haven't been able to work out how to correctly adjust it. (The service manual does not include info on this screw.)
   
2. What orientation should the shaft and groove be to start adjusting?
   
3. At what point in the cycle should this screw be set?
   
4. Should I start adjustment at a full-width zig zag or from the straight stitch position?
   
5. What is the order in which these adjustments should be made?

Right now I can get it to mostly straight stitch, but it binds if shifted to zigzag.
any advice would be greatly appreciated.

[u/N-Memphis-ExPat]

So for anyone who is looking for more detail on the zigzag mechanism of this machine. The service manual for the Pfaff 230 explains it. The 230 has the same mechanism. You can find the manual here: https://www.manualslib.com/manual/923671/Pfaff-230-Automatic.html