TubeNet

I recently bought a 50-year old King 2340, history unknown. I like the horn a lot - I bought one new just like it when I was in high school. (It might even be the same horn!) But even after cleaning, the valves seem a bit sluggish, unresponsive. I'm suspicious that the springs are either fatigued or incorrect replacements as the piston tops are only barely over level with the valve body threads with the top caps off. Just how high above the threads should the pistons set?

How tall would a new spring be with no weight on it?

Thanks!

The pistons on my Kings only rise up over the casings about 1/8" when the caps are off. I use Yamaha Eb springs that are pretty light.