This small leather pouch on the underside of the air motor governor is
connected to the pneumatic stack.  It can be connected anywhere to the
stack, or teed to either one of the hoses going to the Amplifier valve.

Ampico was famous for slight modifications now and then.  Many are
not mentioned in their service manuals.  The purpose of the pouch is
to increase spring tension on the air motor regulator and slightly
speed up the take up spool during loud passages.  During loud passages,
the vacuum on the tracker bar increases, causing the tempo to decrease
slightly.  The pouch was added to compensate for this.

If you decide to use this pouch, be certain that it is air tight,
because leakage will have an effect on the amplifier pneumatic if it
is teed to one of the hoses.

Bruce Clark