This is a good example of what I was talking a bout in my last post, something that one with a little experience with Detroits could spot in a second or two can take much time to explain by typed words.
Hopefully the picture I am attaching will help some. And yes this is from a V-71 manual but they are almost the exact same design.
In the picture you can see the item labeled "Shut-down Latch Assembly" just behind this in the picture not easy to see is the cam like part the latch assembly sets on. It is mounted on a shaft that goes through the intake housing and has a step in it that the spring loader latch should drop into and hold it in place while engine is running. At one end of the shaft running through the inlet housing there should be a small lever maybe 1 1/2 inches long to allow you to turn the shaft to let the latch assembly lock in to the step in the cam on the shaft.
Inside the intake housing mounted on the shaft the little lever and cam latch are mounted on is just a plate of steel that when the "Shut -down Latch Assembly" is pulled out of the step in the cam this lets the shaft rotate and the plate covers the intake to the blower and stops air from getting into the engine thus stopping the engine from running. Note this is intended as an "Emergency Stop" device and should not be used for normal shut downs as it can cause damage to the seals in the blower. The idea is that in an emergency damaging the blower seals is less a concern than having the engine literally explode and possibly injure or kill the operator!
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Did some digging on Google and actually found a page out of a inline 53 manual that shows it a little better:
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Note in this picture the lever to reset the shut-down is mounted right in the cam itself.