The orifice ball often gets stuck in place by carbon, copper fouling and/or rust. If properly maintained, the orifice ball should be free to fall out when the screw is removed.
When you get the ball out you will need to clean the orifice. Use a good solvent to soften the accumulation and, very carefully, clean the hole with a #44 drill bit. The nozzle should also be cleaned and this can be accomplished using solvent and a #38 drill bit. The drill bits should be used only with your fingers and not chucked up in a drill. This may very well clear up your problem.
Also, you might check the chamber closely for rust or pitting as either of these can slow the action enough to create the problem you describe.
