I had the same problem with my deuce. First be sure the engine stop handle is pushed all the way in, then check the engine to be sure the cable is pushing the rod all the way in. If it just sticks out a little bit, it can cause that problem. Put a little PB Blaster on the rod, disconnect the cable and work it back and forth several times, it should spring back freely. If the rod will not free up, remove the two screws on the plate, more PB Blaster and work the internal rod. I also put PBB on the cable from the firewall to the end, just in case it was binding there.
If that was, in fact, the problem and the above doesn't fix it, I can't be of much help.