Kalibrgun Carbine .25 slow leak

[aldea6]

Hi , I've a very slow air leak on my Kalibrgun Carbine . When I remove the air tank from the gun the pressure in the tank remains stable for weeks ; I put air balloons on each side , there is no leak from the filling valve and power valve. As soon as the tank is fitted back on the gun it leaks very slowly , from 200 bar to 0 in a week. No leak from the barrel muzzle .....so what ? An idea , somebody ?
Thanks

 

[Chuck-in-Ohio]

Have you tried soapy waterto try and trace the source of the leak?

Start there, not douching it all over with suds, but using a Q tip or the like to place some around suspect areas and look for bubbles.

 

[aldea6]

Yes , I can try that . Now , after some thoughts , I wonder why is the air tank leaking only when it's fitted on the gun . It seems like something opens the valve ; could it be the hammer touching the valve stem . I have to check the valve spring , maybe it's too weak to keep the valve closed when the gun is cocked ?