Scott,  As mentioned, without seeing it, it's going to be hard to
diagnose.  You did mention a dangling 1/8" line near the motor.  That
most likely connects to the primary regulator, which is right by the
motor.  This regulator also serves as the "Soft" regulator; it's
controlled by the lever up front for "Normal, Dance, Soft".  The loose
tube may be allowing it to play in soft mode, which itself may not be
regulated correctly.

The next place I would look, after connecting that loose hose, is the
Theme and Accompaniment regulators.  Just go ahead and "adjust" the
little arm on the accompaniment regulator to make it play louder.  It's
amazing how little this has to move to make a difference.

I had a similar experience after rebuilding -- lots of suction, but
the stack just wouldn't play.  I couldn't find a leak.  If I collapsed
the accordion bellows by hand, I could get it to play some.

You will eventually want to set this arm for the correct "zero"
setting.  Caution:  make sure you loosen the lock screw before turning
the adjustment screw.

My best guess here.

Jim Quashnock