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Discussion Starter · #1 ·
My California '06 Sprint ST tank vents only to the evap canister. It also has a one way valve in the vent line so expansion air can move out of the tank only, but not back in. This creates negative pressure in the tank. Does anyone know how the tank is actually vented? After any running at all, there is a sucking sound when I open the tank to fill up. Doesn't seem to affect the way the bike runs, but I've never had a bike run well with negative pressure in the tank. I'm very curious about this.

The only thing I can imagine is that the tank is designed to run at a certain amount of negative pressure, and there is pressure regulated vent control in the tank cap seal. So when the pressure gets down to a certain level the cap allows some air to flow into the tank. Since the fuel is pumped, not gravity fed, the low pressure may not matter.

I read the workshop manual section and it describes the evap system. I checked all the lines and they are installed correctly, but the manual does not mention pressure differential. Typically when I buy a new bike, I take all the evap stuff off. Has anyone done this?

Thoughts or insight would be appreciated. Thanks.
 

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Had the same problem and am also in CA.

I tipped the bike once and the safety valve sealed shut from then on I had negative pressure and if the bike sat long enough the tank IMPLODED! it actually sucked the plastic and bodywork DOWN i was freaking out.

I started the bike and pressurized the tank and POP out came the whole tank back to its original shape with no body / paint damage.

So I'm assuming your safety valve in the fuel system has been triggered shut.

--Kory
 

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Discussion Starter · #3 ·
Well, I pulled out the vent valve to the evap canister and realized it is not a one way valve at all. It was just stuck. The way it's supposed to work is it flows air both ways as long as it's vertical. But as soon as you tilt it 90 degrees to horizontal, it doesn't flow in either direction. That makes much more sense.

I gave it a drop of WD, and a few quick shakes, and all is well. If it hangs again, I'm just going to remove it. I don't like parts that don't work the way they're supposed to.
 
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