T8 will not gas

[COB]

Bought a T8 with 2 mags for less than $100. Listed as leaking down the barrel. Additionally, one of the mags leaks. First thing to note is that this is a Gen 1 T8 with the center body screw under the barrel. The Gen 1 also does not have a trigger spring attached to the trigger. So, I went to work on what should have been an easy fix. I disassembled the mag and replaced the O-rings. Lubed parts liberally and reassembled. One problem fixed.
I then disassembled the marker. Removed the engine and replace the O-ring in the power tube. Reassembled the bolt and engine. Found that the pressure relief was missing the spring holding the pin in place. Found a spring, lubed the O-ring and reassemble the pressure relief. Made sure the bolt was pushed forward. Reassemble the rest of the marker. Now for the Head scratcher. Both mags were gassed up with new 12-gram CO2s. No leaks. Insert mag 1 and nothing. Engine does not gas up. Release the mag and you hear the gas pop as the mag comes free. Same thing happens with mag 2. Next, I tried using a constant air mag. Insert mag, turn on air and the back pressure pops the mag out. Gun never gases up. I disassemble the marker and manually blow air through the regulator, and it flows freely. Reassemble the marker and it still does not gas up. Any clue to what I am doing wrong.

[uv_halo]

I would start with disassembling the body, and go over the regulator body with a fine tooth comb. IIRC, it's possible to turn the reg down to the point to where it cuts off air flow. The air path is literally magazine valve (which you can tell is working because you can get that mag popping free). The nipple, and then the regulator and the output of the reg leads only to the fire chamber.

[COB]

Thanks for the input. It occurred to me that the one thing I had not removed, completely disassembled and inspected could be the cause of the problem. I just needed someone else to confirm that it was a possible source. All of my repair knowledge has come from trial and error. This was an item I was hesitant to have come out as an error. A replacement regulator is more than the cost of the gun.

[COB]

Thanks for the input it turned out to be the culprit. I worked on a bunch of these a while ago and had seem to forget what I had learned. The issue was in the velocity adjuster. Thanks again.