I used to have a 3910... it shut down with a fuel shut off. There was a knob below the ignition key. If that's not there, you might have to find the shut off on the injector pump.
Is this something that just happened or has it always been this way or is it new to you. you should have a cable or rod that goes to injection pump if its a manual or an electric solenoid on the pump will usually have a couple of wire going to it if this is the case try unplugging this with it running to see if it shuts down