The problem is most likely the valve travel in the valve blocks used
for these pneumatics.  You do not mention whether you or someone else
replaced the valves.  These valves are usually found both on one box
and they are likely to have thick felt glued over the top hole.  You
may be able to solve the problem by removing this felt.  If the problem
is the pneumatics not opening fast enough this should cure it.

However, if the pneumatic is too slow to close as well, the actual
valve travel is too narrow, and felt removal will not solve the
problem.  You must measure the travel of the valve.  Normal note valves
should travel .035" (35/1000ths) but I usually make sure these two get
more like .045" when I restore them since they must move so much air
out of those large pneumatics.

While you have these valves out make sure the pouch is sealed and the
valve leather is new and that it seals.  I have had horrors with great
looking leather that does not seal so when you close the tracker nipple
and suck on the supply hole there should be absolutely no air movement.
Any air seepage at all and you either have leaking valve leather or the
block itself needs sealing outside.

When putting the felt back on make sure it has enough holes punched in
the center and that they are clear.  These holes are to soften noise
not slow down the air ingress.

D.L. Bullock    St. Louis
http://www.pianoworld.us/