After reading this thread and looking at the pics and diagram, I'm thinking the illustrated fitment might be backward. You seem to be using the "tipover valve" as a way to get air into the fuel tank, and it may work for that in helping to avoid tank suck. But the purpose of the carbon canister, I'm pretty sure, is to collect hydrocarbons that come out of the tank as it sits (if there is a build-up of pressure in the headspace of the tank due to temperature fluctuation) - when the bike is restarted, the hydrocarbons are pulled off the carbon and into the throttle bodies where they become part of the fuel/air mixture introduced to the engine. For this to work, the valve must let air out, but not in. The orientation suggested in this thread lets air in, not out, if I've read the posts right.
I'm interested in this because I recently replaced the stock air box with pods (for the "looks cool" factor) and at the same time removed the carbon canisters and associated plumbing. Since then there's been some occurrences of the bike losing power for short periods during sustained high-way-speed riding, leaving me to wonder whether I have taken care of the plumbing issues properly. (Restarting hasn't been a problem and low-speed riding gives me no problems.) What I've done is to plug the vacuum ports in the throttle bodies and just run the two hoses coming off the bottom of the tank (the one with the tipover valve and another one that's just a hose, I think it went into the airbox) down toward the bottom of the engine, letting them vent to atmosphere. The tipover valve I've left alone, and I believe it's plumbed the opposite to the photo - that is, long end is up, but plumbed into the tank.
I'd appreciate getting anyone's thoughts on this, in the meantime I'll continue researching and check with some non-Guzzi folks for outside advice.