If you get no bubbles at all then it is the needle valve or regulator. Unscrew the bubble counter cap where you fill it with water and see if you can blow through it if not something is clogging it the check valve is in the bottom of the bubble counter where it screws on the needle valve not the top so you should be able to blow through it if not it is clogged.
I took the top off the bubble counter and it is all clear. Not sure how to check the check value at the bottom of it. The reason I decided to spend $375 on this regulator is because I didn't want the challenge of having to buy everything separately and put it together myself. Not thinking I got my money's worth now. LOL.
Is the bubble counter bubbling when you turn the co2 on? If it is then connect just the hose and put the hose end in the water if you get bubbles out of hose then all is well. Then connect the diffuser to it and wait 30-60 minutes for it to start working if still nothing you got a bad diffuser or it needs extremely high working pressure which is sketchy past 50psi. That is all it can be you have isolated everything else.
Ok - there were bubbles coming out of the end of the tube. I replaced the brass check value with a cheap plastic one I had - we'll see if this works. By the way - I cannot blow through that check value - I should be able to right? Perhaps it is a bad valve?