Hi Brian,  I'm an electronic engineer but ashamed to admit that
I don't know much about motor theory, but I can tell you a few things:

1. Switching the wires does not change the direction of a 1-phase
electrical motor.  It will change the direction of a 3-phase motor,
but not a single phase motor.

2. Running a pump in the wrong direction will create an equal vacuum
however it is a request for a minor catastrophe.  The large wheel of
the pump is screwed in place and the arrow shows the direction of
tightening the screw.  When the motor is running the wrong direction,
you constantly are working to loosen the screw of the pulley, and one
day it just may fall off -- I wouldn't want to be under the piano when
that happens.

How did this happen?  I'm only speculating here, but Ampico had little
presence in Britain, as opposed to Duo-Art, and the Yankee pianos don't
have the great popularity outside the States, so I can only guess that
your Ampico started its life in the USA.  Whoever brought it over
probably decided to replace the original motor with a motor from a
Duo-Art of the same period, not realizing that the Duo-Art runs in the
opposite direction.  They turned it on, it worked and they were happy.

I run my Ampico with a transformer; it works, but it slows the speed of
the motor by 17% -- and I feel it with peak vacuum draw need.

Eli Shahar

 [ Many years ago a hurricane wrecked all the power lines to a small
 [ town in West Virginia.  After the power company made temporary
 [ repairs the 3-phase power was reversed.  National newspapers then
 [ reported that "clocks ran backward, escalators ran downhill, and
 [ at the bakery the freshly baked bread moved back into the oven!"
 [ -- Robbie