Check for air obstruction inside the tracker bar, kinked hoses, etc.
Test the stack with all tracker bar hoses removed and open and close
the nipple with your finger to test for loudness and repetition.

If you lose too much vacuum with all nipples open, put little pieces
of tape over all of them and test one-by-one.  If the nipples are hard
to reach, use a short piece of tubing.

You need to know if the problem is in the stack or elsewhere.

Gordon Ramsey