If the co2 is leaking out the muzzle as soon as you insert and puncture a new cart, then do as I suggested and cock the gun prior to inserting the cartridge.
I am thinking of a new poppet that was no good and I ended up using the old one on a C140
It doesn't hurt to put the poppet in the valve face, and hook it up to a drill and give it a seating spin.