Vintage Double Hose

I was far too enthusiastic when I disassembled my Navy Approved and I don't recall how tight the two screws that hold the horseshoe in place were.

I've tried putting them in all the way, backing them off a tad so the pin fits. I tuned the 1st on 300 PSI until the second hissed a bit. The problem is that it honks when I breathe on 300 and 2000 PSI.

I tried backing the screws out 540° (1-1/2 turns), tuning it to hiss at 300 PSI and it honks on light breathing and less on a fast breath. Any farther than 540° and the 1st stage adjustment seems wrong.

This can't be normal. Lacking a venturi I expect the pressure it's backing the diaphragm off when cracked and the second stage is oscillating between open and closed.

Also, in this case, the back can isn't the original. The second stage is positioned at the inspiration horn.

Do you have the correct IP, 130 psi at 300 psi tank pressure. The factory adjustment is 2 turns out from the bottom but I will measure the height of the ends of the horseshoe where it contacts the diaphragm and get the height as even as possible between both ends even if it requires one screw to be different from the other.
Start at 2 turns out, try not to go in to even out the horseshoe. You can also try switching screws from side to side to see which provides the better result.
The ends of the horseshoe should be smooth, you find most have a groove cut in them from the tabs on the diaphragm. Gently file them smooth and slightly rounded.

The ends of the horseshoe need to be equally centered against the diaphragm tabs. I believe the honking comes from the diaphragm tabs and the ends of the horseshoe not being aligned and also too low a horseshoe setting. I like to have tabs touching the horseshoe at all times.

The rear can has no effect, some late DA Navy's had the Aqua Master rear can.

They can be made to be pretty decent breathers but the require more attention to detail than an Aqua Master or RAM. Sort of like blueprinting an engine.

Captain Tom walked me through a honking DA on the forum as well, if it helps:

viewtopic.php?f=4&t=5022&hilit=honking

Like Tom said, awesome regulator but they require a lot more attention. They definitely make you appreciate a venturi assist