The valve is supposed to be used as an emergency off valve. The manual says it should be wired open with thin safety wire (.020??).
Just to add a bit - early 150s (I believe all straight-tails) did not call for safety-wire on the fuel valve. I believe that was added on the slant-tails when the fuel valve was relocated from vertical to horizontal position.
In any event, the fuel valve should be checked every annual to make sure it actually stops the flow of fuel. Note - if the valve is shut off while the engine is idling, it takes a surprisingly long amount of time before the engine actually stops. Something on the order of 2-3 minutes. At cruise speed it happens much faster, but it’s still not instantaneous.
