Hi All,  One of the most common problems with the Sting II is poor
regulation of both the piano action and the 'stack-to-action'
adjustment.  If the let-off is around 1/4" and there's lost motion of
1/8", you've already lost of 40%+ of the power.  (Remember, the stack
is below the keys.)

Then, factor in the power loss with an 1/8" of lost motion between the
stack and the keys, and you can see that only about 1/8" of the travel
of the bellows is actually making the hammers move.  So, the total
power loss would be in the 60%-70% range.

Also, I've encountered a number of Sting II players where the striker
pneumatics were halfway closed when at rest.  That being the case,
the strikers have very little power even though there's plenty of
vacuum.  Unfortunately, fixing the problem is rather involved because
it usually requires adding spacers between the tiers so the pneumatics
can open more.

It may also be that the cloth on the strikers is getting stiff.  This
is not uncommon in units that were used very little -- which is, sadly,
too often the case.

Lastly, and generally speaking, if the vacuum level drops off by 5"
with just four notes playing, it's a good bet that either the valves
aren't fully seating (exhaust side) or the bellows cloth has gotten so
stiff that the rubber has cracked at the folds -- especially near the
front -- and the cloth is leaking badly.  Or, it could be a combination
of both problems.

Musically,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA