Yamaha - Check Valve Assembly Fuel System Protection 6F6-11370-01-00. Overview. If you've spent any time working on Yamaha fuel systems, you know how important it is to keep flow moving in one direction-and only one direction. This check valve assembly plays a quiet but critical role in preventing backflow that can cause hard starts or inconsistent fuel delivery. It's one of those parts you don't think about until something feels off on the water. When it's doing its job, everything just runs sm