I am not sure what your confusion is exactly but noticed you state “…lever on the valves.” in your reply.
I have an L185 so a different model but the throttle and orientation of part are very similar to the pictures above.
The throttle is a lever that pulls back to increase RPMs and forward to lower RPMs as @Lil Foot
describes. There is also a foot throttle. Both of them only return the engine to idle. To shut the engine off the lever that has the yellow arrow pointing to it (vertical plate steel with a finger notch) has to be held up for a few seconds (with the throttle being at idle).
I have never looked at exactly what is moved but it is in the injecto pump to cut fuel off completely through the pump. It has nothing to do with the release of compression in the cylinders of the engine. But there is a decompression knob on the dash to pull out to help the engine start (and probably for emergency shutdowns) but should not be used regularly for stop the engine. I have also read that some tractors had a knob that was pulled out to shut down the engine. But I am pretty sure that knob does the same thing as the lever discussed above and shuts down the fuel flow through the injection pump. I think that the cable would be running to the inj pump to pull the rack closed.
PS: If you reply to a post and type inside the words “quote” your reply is inside the quote along with the original text. Put your text outside the words “quote” and it works and looks better. I had to copy your text and paste it above to make it look like I replied to your post.