That's funny. My used King Beat had an extremely hard spring. I could not play with it because the cap nut had dropped out before I reached the right tension. So I modified the spring unit. Since then, the pedal is a dream. Now the question arises whether my previous owner has installed a harder spring or Tama has changed something.I had 2 at one time when I had twin kicks and I'll say they're bulletproof as far as durability. I did find that over time, the spring would get pretty weak and no amount of turn on the adjusting handle would help.
I'd gut it & see what's up. If the spring can be replaced with something modern, you'd have a pedal that would last for life.