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Old 03-04-2011, 12:03 PM   #39
The Griz
North Forest Rider
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Joined: Nov 2008
Location: Minnesota
Oddometer: 3,787
Originally Posted by MTrider16 View Post
Don't most motorcycle tanks vent to atmosphere? Does the Euro version connect to the airbox?

Yes, historically, the gas tank pressure relief opening on motorcycle gas tanks vents out to the atmosphere via a hose. However, refer to post #17 for an explanation as to why the US EPA has nixed the "out-straight-to-the-atmosphere" design:

It is important to understand here that the F800GS gas tank design, as far as venting out and sucking in goes, is no different than any other motorcycle (on a BASIC level, so no need for brainiacs here). The F800GS tank vents out and sucks in when necessary, just like a 1987 KLR650 gas tank vents out and sucks in when necessary. Regardless of whether we're talking about a carbeurated 1987 KLR650 or fuel injected 2011 F800GS, both of these bikes vent out when pressure becomes too high inside the tank. They both also suck air in to replace the fuel that gets used by the carbs and engine. It's a back and forth suck/blow () scenario, and which one the tank does depends completely on many factors: atmospheric pressure, temperature, humidity, and how much the fuel level in the tank is dropping.

PS...I personally do not subscribe to the belief that +/- 5 PSI could actually expand and contract the red THICK inner bladder on this bike enough to crack the tank's outer, much more pliable black shell. It's just not enough force. And besides, I was able to inspect the first cracked tank that was taken off of my bike at the dealer. The outer black plastic shell is pliable enough to be able to withstand a decent amount of flex. Also, it would take a lot more than 5 PSI to expand and contract the thick red inner bladder enough in order to inflict enough pressure or force on the outer shell to crack it. It's just not possible. I had the tank in my hands and thoroughly inspected it.

Outer black plastic cosmetic shell: Thin, pliable, soft plastic.

Inner red gasoline bladder: Very thick, very stiff, hard plastic.... as in not expandable.
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