There was a previous version of the OS 91 Surpass. OS doesn't present any parts for it.

That regulator is a balanced "zero pressure" regulator. It will not let any fuel get past it unless there is a slight suction on the carburetor side. In other words, it is not a regulator of higher pressure to lower pressure but a "demand regulator". If there is no vacuum on the outlet side the regulator, there will be no fuel allowed to go to the carb.