Ensure the spill valve is properly seated.  Disconnect the stack
supply hoses individually from the stack, one at a time, and stop
them off to the pump to see if there are leaks at the stack or pump.
Check the crescendos to see if they are collapsing.

Check the movement of the diving board valves to see if they're
permitting sufficient movement to allow for proper air passage.  See
that the cancel valve for the three expression valves is functional.

Tom Binnall
Tacoma, Washington