It is just a simple check valve you don't need it. It only comes into play if you dump the bike and even then it really wouldn't do much if you have a vented cap and even with the stock cap not sure it would do much. You can also check the vent hose under the bike to make sure a mud wasp didn't nest in the vent tube or a piece of dirt blocking it or something. Try just pulling the valve out of the line and take it for a ride. If the bike runs good then you know either the valve isn't working or there is a blockage after the valve.

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