Strange Problem

Try these steps in this order:

1.Use extreme rage mineral oil/marker oil or hoppes oil to oil the bolt.  Put like three drops on it and also put some in the ASA and fire several times. If this doesnt do it then go to #2

2. Take the expansion chamber off and hook up th ehose normally adn then try it.  The fact that it works on its side is tellin me that it isnt letting enough co2 through when the co2 has to move up the chamber and the liquid is like not getting any gas to the valve.

3.  Fill your tank, not the likely soluton but possible.

4.  Try a new expansion chamber.  This one could have too many gas passages and so when you fire fast it takes too long for the gas to get to the valve cause it has to travel too far.  That would explain the stuttering and not recocking.  Not likely but possible. 

5.  Take the gun to the proshop for inspection.  Check fo kinks in the hose or blockages and even a leak.  They will take the hoses and chamber off to check for blockages also but it is possible that that is your problem.

As others have said lack of oil could be a problem. Loose screws that hold the power valve in the marker could also be it. Or my best guess is a bad "O" ring on the hammer (rear bolt) so that there is leakage the prevents the bolt from being blown all the way back to the cocked position.