I have attended several Piano Technicians Guild meetings, seminars and
conventions.  They are excellent sources for information about these
type of subjects.  The organization is loaded with people who disparage
automatic musical instruments, and player rebuilders clearly do not get
the respect they deserve.  The editor of the journal told me that he is
taking no articles about pneumatic instruments.  I tolerate unimaginable
"nonsense" from the organization because I learn much about pianos.

Check first for tight action centers (where the shank, butt, or whippen
is pinned into its flanges).  Check for key bushings binding on front
and center rail pins.  Check to see that the action is in regulation.
Check to see that there is no friction from the parts that move against
each other.  Check for action geometry problems.

If nothing else works, (as a last resort) add and subtract lead weights.

Bill Maguire