A surgical severing and stapling instrument clamps tissue in a staple applying assembly comprising a lower jaw of an elongate channel holding a staple cartridge and a pivotally opposed upper jaw (anvil). A firing handle drives a rack in a handle connected to a firing rod and bar that pass through an elongate shaft and into the staple applying assembly to sever and staple tissue. Upon release of the firing handle, a retraction spring assists in withdrawing the rack and other firing components. To advantageously assist in firing, a spring biased plunger is cocked prior to firing to impart assistance upon depression of the firing trigger. Alternatively, a torsion coil spring ratchet mechanism is preloaded to act through a gear into the rack to assist. As a further alternative, a retraction spring is preloaded and disengaged until the rack is fully fired.
