With the key pressed down, use a large crochet hook or similar to pull the (key's cradle) end of the spring say 1 mm away from the cradle. Then return it to the cradle. Play test it.
If that does not help, try 2 mm. Etc. If the spring gets too weak, then unhook it from the cradle and bend more curve in it.
But it is quite common for a spring to be over-tensioned to band-aid another problem, e.g. poor pad alignment over the tone hole, to make a "dead" (say over-hardened with age) pad seal better, or to overcome excessive friction in the hinge. If so, these issues need to be properly dealt with first.
If that does not help, try 2 mm. Etc. If the spring gets too weak, then unhook it from the cradle and bend more curve in it.
But it is quite common for a spring to be over-tensioned to band-aid another problem, e.g. poor pad alignment over the tone hole, to make a "dead" (say over-hardened with age) pad seal better, or to overcome excessive friction in the hinge. If so, these issues need to be properly dealt with first.
