Article [11] ST1100 - How to do an emergency bypass of the fuel valve

[Andrew Shadow]

If a carbureted bike with a manual shut valve in the on position tips over fuel will leak till the tank reaches a certain level or the bike is upright again. A vacuum shut valve prevents the fuel from the tank from leaking out in a tip over or a crash situation.

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  Fire Hazard Prevention: In the event of a crash or tipped vehicle, a vacuum petcock ensures that fuel does not continue to leak out, reducing the risk of fire.

While that is an additional benefit, according to Honda the primary reason that the automatic valve was included on the ST1100 was as part of Honda's methodology to meet emissions requirements.