Re Jeff Bryner's post, I found that a leaky hose will cause this to
happen.  A friend's Ampico would exhibit exactly the same symptoms
you describe.  In this case, it was caused by a piece of lead tubing,
with several pinhole leaks, in a short segment from the tracker bar.

I cut out the defective segment and inserted a short piece of rubber
stock.  Problem solved, for now.  I found the leak by having my friend
blow into the tracker bar with a hose and listening for air with
another piece of tubing in my ear while laying down under the drawer.

Replacing all of the lead from the tracker wasn't an option at that
time, but would have been the way to go if finances were better.

Hope this helps!

Bob Hodge