Hello Joe and MMD'rs,  The earlier Ampico A sustain and hammer rail
lift mechanisms were a little slow, primarily due to the limited
airflow capability of the single unit valve that operated each of them.
The rolls made at the time the pianos were current anticipated the
relative slowness of operation, and so the overall performance was
usually acceptable.  Later model A's were a little faster, sometimes
being fitted with two 3/8-inch I.D. tubes feeding the sustain pneumatic
from the valve assembly.  A few very late model A's used the very
sophisticated(?) sustain pneumatic valve later used on the Model
B Ampicos.

It sounds like you might have an internal restriction or blockage in
the actuating pneumatic or excess friction in the associated operating
linkage.  Try lubricating the friction points of the linkage with
a dry Teflon lubricant.

Model A uprights frequently used two unit valves in parallel (one
with a bleed and one without) to control the sustain pedal.  The same
approach might be used along with a second 3/8" tube if the first
"remedies" don't solve it.

Make sure the valve itself is not contributing to the sluggishness
because of insufficient valve travel, too much restriction in the
muffler felt, or mis-alignment in its mounting.

The same comments apply to the hammer rail lift, but it is not
necessary for it to be as fast as is desirable for the sustain.

Finally, (should have been sooner...) check the amount of damper lift
and lost motion.  There should be just enough lost motion to ensure
that none of the dampers are held off the strings when the pneumatic
is open.  The sustain pneumatic should lift the dampers just enough
that the trichord wedges are just clearing the strings.  This is often
less than they lift by the keys.  Since there is no stroke limit
adjustment screw, it may be necessary to utilize a small increase in
lost motion to limit the damper lift.  Reducing excess automatic damper
lift effectively increases the sustain pedal response time.

Hope this helps.
Bob Hunt
Kennebunk, Maine