Up front, I am not an expert. Having said that when I was fiddling with mine I ran into the same thing. Near as I can tell the spring is for closing the valve as it cools, not forcing it open as it warms. What appears to happen is, as it warms the spring relaxes it's push toward closed and the force of the exhaust pushes the valve open. When you shut the engine off and the spring cools it pulls the valve closed.
Last edited by Tiny; 10/08/2021 3:09 PM.
