PCV is a controlled vacuum leak, so it will add some air to the engine and lean it up slightly.
I have never seen a Marine engine that used it, or a carb that was set up for it, but I suppose they may have used PCV in a few applications.
It's actually a good idea, especially if the boat is used under light to moderate load a lot, as PCV would burn off the crankcase vapors produced like an automotive application.
What may also be happening on this new fuel is that the engines want a richer mixture, and the carbs are a little lean right to start with, so they don't want or like the additional air from the PCV system.......Cliff
