I think it actually winds up, but yeah that's the idea.
The weight and exhaust flow open butterfly inside manifold.
There was also another spring, a counter-acting spring. I don't think that one is bi-metallic.
I had an engine sitting that I trusted to be right and assembled new one that way and it works.
BTW: If not obvious the shaft needs to be clean so it can move freely. Penetrating oil and light tapping side to side usually free them up.
Pete
