The velocity adjuster is a rex dialer. You turn it counter clockwise to increase velocity. Try 1/4 turns at a time. Overcompression of main spring can cause lower velocity. You stated your marker has been sitting a few years. Your reg's orings may be dry, at the very least, causing it to stick and not recharge. Try dropping a 3-4 drops of gold cup oil or equivalent into the asa and dry fire it 20-30 times to circulate the oil into your reg. Too high a psi can also cause low velocity. As a general rule, you want to set it at 300 psi. My 2 eclipse cockers, stock, seem to like 230-260 psi. Hope this helps. It's a beautiful and rare marker nowadays. Market value on yours is about $400-$500 depending and condition and if its totally stock.