[pianotech] Bobbling hammers and jack spring pressure?

[Jon Page]

Bobbling hammers can usually be cured by tweaking the interrelationship
of key dip, hammer blow and Let Off.

If the problem persists when these approach their maximum allowable settings
then look at the Key Ratio.  Moving the capstan back on the key will cause the
end of the wippen to move through a greater distance and allow the 
jack to clear.
This will raise the touchweight, although I can't imagine it being necessary
on a Yamaha but it just might be a case of 'whatever works'.
-- 

Regards,

Jon Page