Mine will dump 15. I can't remember what I have in there for springs.Are you sure your transfer ports are lined up, between the valve and the barrel?
Maybe I missed it here, how did you fix the pump lever?
It requires a weak valve spring. You should have to cock the gun to pump it. That's the way it was, from the factory. Did you tighten the hammer all the way in? That also makes it shoot slower / retain air.