with a cocker there isnt really a dwell, the spring tention and ram forward time/delay (forgotten the acronym) is what controlls velocity in the same way as dwell does with other markers, if its set at factory fast then the problem lies alsewhere, remember that at certain spring tention settings increasing your high pressure can actually lower the fps because the pressure behind the valve is too high for the inertia of the hammer to open it sufficiently.
try upping your input psi, if you get a lower fps then increase the spring tention slightly.
try upping your input psi, if you get a lower fps then increase the spring tention slightly.