Bobbling hammer in an Upright Piano. Fix it’s yourself.

[maxim_tuner]

https://youtu.be/sV-j_doRibM

• 1 remove the lost motion by raising the capstan.
  2 increase key dip by raising hammer height by shimming the balance rail.
  3 You might be able to help it by bending the 'backchecks' closer. Bending the rod with the green felt just slightly forward even with your finger while supporting it will work generally. This is called ‘the butt catcher’.