Hi Lucas

​If memory serves me correctly, this subject was either covered very early on in this forum or a long time ago in the Yahoo Group portable typewriter forum. Use an elastic band to hold the carriage release lever against the platen knob so the carriage will slide completely freely. Using a known accurate spring balance, pull the carriage against the mainspring, tension should be around 2 pounds at mid travel. As I say, this is just going by memory.

As for over-winding the mainspring, I would imagine the spring would likely tear from one of its moorings if the spring dead heads before the end of carriage travel and the carriage is thrown to the right. The mainspring system on a typewriter is much like the recoil starter system on a small engine. If the cord is set to dead head before the spring, the worst you'll do is to break the cord. If the spring deadheads before the cord though, you'll end up with a torn anchor point or a broken recoil spring. Hope this gives you something with which to work. All the best and happy new year,

​Sky