This is from memory:  What makes an Ampico A play loudly or not --
without tearing it apart -- is hard to say.

To fix a reproducing piano, you need a vacuum meter.  This can be
a gauge that you connect to the inputs or a water tube in the shape of
a "U".  The problem is that if you want to measure high vacuum levels
such as the output of the pump, you would need a U-tube that is at
least 50" high plus, and if you want to measure accurately intensity
drops and zero-intensity playing, you need greater accuracy than you
get from most dial vacuum gauges.

1. Start with the pump.  How much vacuum is the pump putting out if you
don't have anything attached to it?  The pump should easily give you at
least 40" of vacuum if you measure it with all other inputs closed off.

2. What about the pump release valve?  It may be set incorrectly.
There's a black lid on the head of the pump with a pneumatic that
closes with a spring on it to regulate the vacuum.  The loud setting
closes this, medium and soft settings release it.  Setting for medium
is with the pneumatic open -- it regulates the amount of vacuum by
adjusting the spring tension for this release.  Setting for loud is
by the amount of travel that the pneumatic closes (thus adding more
tension to the spring and increasing the vacuum).

3. Assuming the pump is okay, what is the pressure drop from the stack
itself?  If you are inputting 12" of vacuum on the inlet to the stack,
do you measure 12" of vacuum on the tracker tubing or 4" of vacuum?

Do you have a test roll for the Ampico?  This is very important for
setting the piano up to play correctly.  Each test has a different
measurement that you're supposed to make, and tells you the results you
need and which screw or nut to adjust if it's off.

Eli Shahar