Sounds like just a regulation problem if everything else has been correctly restored. That's the problem. That's why I had to write my own technique, after studying the system. They take a LOT of fussing with to be any good. The adjustments interact.
Timing is critical.
It is self-compensating anyway, so as soon as the pressure in the stack gets to a certain level regulated by the spring, the flap begins to close, or at least to regulate at that level. Just like the Ampico. I might as well do two for the price of one. I've done a number of those pumps and have had great luck with them. Little bitty fellows.