what does that 5/16 hex screw do...

[The Chairman]

Regulators can free flow for many reasons. Changing the IP blindly in an attempt to stop the freeflow can render your regulator inoperative at depth. It is not wise to turn an adjustment here or there on a regulator if you don't know what you are doing.

 

[SparticleBrane]

NetDoc is right. I have a DiveRite RG2500 setup on which I keep my primary reg VERY 'loose' in terms of breathing. Usually, turning it mouthpiece up, even very slowly, is enough to make it freeflow. However, that doesn't mean there's anything wrong with it--just means that I have it set to breathe very easily.
My backup reg (of the same model) is set to breathe as hard as possible. I have yet to make it freeflow underwater, no matter what I do.