Hi Harro10,
The problem with simply tightening the orifice to "stop the leak" with the Mares Abyss is that you are also lowering the demand lever.
Adjusting this regulator is a balancing act between orifice depth and lever height. Moving the orifice also moves the demand lever.
Properly tuned, your Mares Abyss should be stable (no free flows) but breath very easily.
With this regulator, when it is pressurized, you should be able to gently shake the 2nd stage in a quiet room and hear a light tapping of the lever against the 2nd stage diaphragm, like tapping a finger nail lightly on an aluminum can... this indicates just a slight bit of free play (1 - 2 mm) between the lever and diaphragm.... you should not hear a loud "clacking" like shaking a pebble inside an empty can, that means there is too much free play... and you should never hear anything when you shake an unpressurized Mares 2nd stage (in an unpressurized state, the lever is in full contact with the diaphragm, there is no free play).
A touch-up tuning is sometimes needed, like Scared Silly describes; and in a pinch, yes you can just remove the 2nd stage and use a hex wrench to carefully "stop the leak".... but be aware that more than just a "tweak" will begin to seriously de-tune your 2nd stage since you are not only increasing cracking effort but also lowering the demand lever when you turn the orifice clockwise (and raising the lever when you turn it counter-clockwise).
Lowering the demand lever causes the 2nd stage diaphragm to have to travel further before contacting the lever and open the demand valve; a lever set too low may not fully open the 2nd stage demand valve during inhalation, turning your sweet-breathing Abyss into a "dog".
My quick and dirty pre-dive and between servicing checks for my Mares Abyss's (and other Mares 2nd stages):
1. Vacuum test for leaks (see couv's excellent checklist that is "stickied" at the top of this forum).
2. Pressurize reg... purge a few times, check for freeflows. Also make sure that purge button only travels 1-2mm before air begins to flow. If it travels further than this, the lever may be too low.
3. Shake reg, listen for the slight rattle to make sure lever is not set too high.
4. Breath reg.... with experience, you'll know how the reg should "feel" when it is well tuned.
Finally.... I love my Abyss regs, but simply hate that the newer Abyss regs have plastic orifices. I really think that this causes some tuning issues, i.e. free flows, that I do not see in my older Mares Voltrex 2nd which has a metal orifice.
Best wishes.
