Hi Duaine,  It's been awhile but I had a similar problem with a Haines
Brothers Ampico A model.  On mine there is a rod that runs from the
Tempo lever to the back of the drawer to move a valve.  The valve is
comprised of a piece of leather that slides over a hole to allow more
or less air to enter a wooden box.  (I think the material was leather;
not sure.)

The shape of that hole is, as best as I can describe, shaped like the
profile of an old style drinking glass called a "yard".  That shape is
created with a rectangular piece of plastic or Teflon type material
tacked down over a regular round shaped hole in the wood.  The problem
on mine was that the plastic has cracked and the edges of the cracks
had curled upwards and blocked the travel of the leather valve.

That was early in my player repair "career" and so I wasn't able to
find a replacement piece, so I made one.  The Tempo on mine is about
10 units off (whatever the units of Tempo are!) and so I adjust
accordingly.  Hope this helps.  I apologize for putting this all in
such layman's terms but that's really all I am.

Paul Meehan