The OPSS controls nothing more than power to the fuel pump. If there isn't oil pressure, ie if (1) the engine won't start or shuts down or (2) there isn't any oil, it turns off the fuel pump so (1) the carb doesn't flood and fill the engine room with gas or (2) the engine doesn't seize catastrophically. Although it probably will anyway.
So this means the engine usually is asked to start up without any power to the fuel pump for several seconds, relying on residual gas in the carb bowl to start the engine. Once the oil pressure builds a bit, the fuel pump kicks in and catches up. If the OPSS connections are loose, or the switch has failed, the engine will literally run out of gas.
This is easy to see, and diagnose if there's something wrong, with an inexpensive inline fuel pressure gauge. (And potentially easier to see with a more expensive sort of fuel pressure gauge, like some of the white-glove guys around here have.)
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