I have a guide to restoring the Ampico A on my website which may be
helpful.  See: http://antiquemechanicalrestorations.com/Ampico_A.html 

Whenever I restore an Ampico A, I add paper front-rail punchings to the
top of the rewind valve in the governor.  This limits the throw of the
valve and in essence chokes the vacuum supply to the air motor on
rewind.

The air motor speed can be slowed down even further after this
modification through use of the tempo lever during rewind. Cut the
travel of the valve down to about 35 or 40 thousandths and see how you
like it.

Paul Manganaro