Well in actuality the cam only “fires” the injectors. The fuel is actually controlled by a mechanism called a control rack which has fingers that move plungers in and out of each injector. When a detroit is shut down the rack defaults to the full fuel position to aid in starting. The problem comes in when the engine sits for a long period of time. The plungers get stuck in the injector bodies and it sticks the rack at full fuel. In the late 70s detroit updated the design to use spring loaded fingers so that one stuck injector wont stick the entire rack and help prevent run away. With this design update detroit did away with the emergency shutdown flap located on the inlet side of the blower.