Check Valves on Manifold

Anyone offer some insight into how the check valves work on the manifold of older outboard Johnson and Evinrude Outboards. Many Johnson/Evinrude motors use these with the fuel recirculating system. OK, I get that. My specific motor is a 1984 Johnson 90hp V4 but these nipples(check valves) are used on many outboard models. The factory service manual describes how to check them, inspect that they function correctly, and they should only flow one way...I pulled the ones off my engine and there is no one way valve system, just a filter screen. The replacement check valves from the marine engine site look exactly the same so what is the deal. Have mine simply been modified and a replacement actually has a one way valve?? Anyone help...Thanks

Copy that, I have pulled them off the motor to inspect. No bearing or any such device to create a "one way" . There are 4 and I understand how the fuel recirculating system works but just don't see how these nipples function as "check valves". As I mentioned, nothing but a filter screen and no valve device.? Anyway, thankyou for the reply

Simply check to see if you can blow through one way and not the other.-----------If it does not work that way , it is defective !----------They call them check valves for a reason !

The screen is to filter debris from entering the duck tip like rubber check valve that is in back of the screen. The duck tip valves in your check valves are faulty. Replace them.

Their purpose is to recirculate the unburnt fuel back into another cylinder for reuse. Running a engine with just one faulty check valves will result in one cylinder running lean, the other cylinder rich.