It's your lug. Your firing point is behind your recocking point, and although it will fire without air, it'll still recock before it fires with air. You don't need anything new.
Just raise your lug until it no longer catches the sear when you cock it without air, then lower it until it just barely catches and add a turn.
It should fire fairly close to the very front of the trigger pull, but not so close that the safety stops working. Not sure if those old CCM frames have safeties, so that may be moot.
Ex of a good trigger pull:
If your recocking point gets too close to the firing point, you'll get blowback, if it overlaps it, you'll have what your marker is doing. However, there is a perfect middle point where it's not too far back as to cause undue short stroking, but close enough that the ball leaving the barrel will create a vacuum for the paint in the feedneck. That's a good place to be.
F - Fire point
R - Recocking point.
Last edited by Dk-79; 10-07-2012 at 07:05 PM.