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Fuel Tank Breather Hose

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Would someone please explain the function of the dirt bike fuel tank breather hose? I realize air has to enter tank from the top or a vacuum would form and fuel would not gravity-feed down to carb. But, then why don't street motorcycles have them? Is it because of the extreme sloshing dirt bike tanks get that precludes the use of street motorcycle gas caps, caps which are presumably designed to admit enough air to tank without a hose?

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1 hour ago, suppresst said:

Would someone please explain the function of the dirt bike fuel tank breather hose? I realize air has to enter tank from the top or a vacuum would form and fuel would not gravity-feed down to carb. But, then why don't street motorcycles have them? Is it because of the extreme sloshing dirt bike tanks get that precludes the use of street motorcycle gas caps, caps which are presumably designed to admit enough air to tank without a hose?

The hose is not necessary, as the check valve is in the cap.

It's probably for dirt, rain/creek water, and debris in general.

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4 hours ago, suppresst said:

Would someone please explain the function of the dirt bike fuel tank breather hose? I realize air has to enter tank from the top or a vacuum would form and fuel would not gravity-feed down to carb. But, then why don't street motorcycles have them? Is it because of the extreme sloshing dirt bike tanks get that precludes the use of street motorcycle gas caps, caps which are presumably designed to admit enough air to tank without a hose?

Street bikes have to meet emissions standards, just like your car/truck. The venting is a bit more elaborate.

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