Replace battery with high quality brand
Check QEV diaphragm. Should be in 1 piece.
Replace rammer o-rings.
Also be sure to open the on/off knob a 1/2 turn and check again.
Could also be the bottle reg on/off combination.
If this is your problem you can simply solve it by removing the on/off knob and placing a small #4 o-ring on front of the pin.
This will stop the pin being pushed to far and will also ensure your on/off knob will not come loose while playing.