X7 Leak

Coulple of things to check: Is the marker cocked when you are screwing the tank onto the marker? If the tank is screwed on when it's uncocked, the bolt can push on the valve pin and allow CO2 to leak through the valve. Have you oiled the marker? Dry o-rings can allow leakage. If air/CO2 is leaking down the barrel, something the valve must be allowing it to pass through. Perhaps you have an old/damaged o-ring in the valve, or perhaps it needs oil. Are you certain it is coming out of the barrel? If not, than check your gas line o-ring to make sure it's clean and oiled.

Im posting a little late probably,but anyways.I had exactly the same problem.( Co2 comes out my front barrel Tippmann X7) opened it, took out the powertube and valve.stripped the valve completely,replaced o-rings and still the same prob..then to test i put a o-ring in front of the valve plunger ( valve plunger is inside the valve) and the leakage stopped.( obviously after one shot the leak is back because the o-ring in front of the valve plunger comes loose because its not suppose to be there i was just testing...SO in my oppinion the fault IS THE VALVE and to go more in detial i think its the valve plunger...Any way i baught a new valve and the problem was fixed.for even more detailed explenation email me at shaunnstrydom@gmail.com ill reply happely as a tippmann x7 fan :)