[screwdriver]

ive had this with most m4 variants even a marui, once you have the motor in place and the wire not trapped in the grip the motor should move in and out freely , ie push motor in and the motor spring should push it back out freely, once this is sorted the grip cap can go back on and adjustment screw shouldnt need touching.
your motor sounds like its jammed too far in the grip so not allowing spindle to turn as overtensioned