"Tip Over Valve"

[creaky99]

I'm going over my '98 V11 in preparation of (hopefully) heading for FL early March. I have changed the fuel filter. PO has removed the "tip over valve", called an "oil breather valve" in the fiche. There is another valve placed horizontally beneath the tank in the same recovery hose as the tip over valve, it is called a "valve" in the fiche. Why two valves?  Should it be left in place? 

[Wayne Orwig]

The tipover valve  is meant to stop fuel from directly blowing out the line if the bike falls over, and soaking the charcoal canister. It must be vertical.

The over valve keeps the tank from just breathing in and out through the charcoal. It take a little pressure, before it opens. I believe it is directional. It takes more to work one way than the other I believe. With it in place, you will usually get a little vacuum when you pull the gas cap. Not a lot though. Maybe the main point of it is to keep moisture out of the tank since it isn't freely breathing all the time. Not sure.

I keep mine stock, and they just work.

[creaky99]

Thanks Wayne. I removed the 2nd valve under the tank and it is one way from the tank to the canister. I have read that a lot of guys remove the tip over valve citing problems with tank pressure. Not sure at this point if I need to buy a new tip over valve to replace the missing one or not, guess I'll wait for some more opinions.

[sib]

The tipover valve  is meant to stop fuel from directly blowing out the line if the bike falls over, and soaking the charcoal canister. It must be vertical.

The over valve keeps the tank from just breathing in and out through the charcoal. It take a little pressure, before it opens. I believe it is directional. It takes more to work one way than the other I believe. With it in place, you will usually get a little vacuum when you pull the gas cap. Not a lot though. Maybe the main point of it is to keep moisture out of the tank since it isn't freely breathing all the time. Not sure.

I keep mine stock, and they just work.

On my '13 V7 Stone there's only one valve in the tank vent line, it's horizontal and it is indeed easier to blow through it in one direction than the other.  I believe you are correct that it serves to prevent free diffusion of air into the tank.  This helps to prevent atmospheric moisture accumulation in the fuel as well as cutting down on fuel evaporation into the atmosphere (although the carbon canister also helps here).  This valve is the source of the mysterious groaning sound that these bikes occasionally make while parked.  It's possible that the valve also serves to block liquid fuel from spewing out if the bike is tipped over, but I haven't directly tested that.  The Guzzi part number is 860138 and it is installed with the blue side toward the fuel tank.