Roll Over Valve Question

Found out the hard way that over filling the tank floods the engine. The cure was never fill above the welded-in internal baffle in the tank. Then I installed an ISM tank with no baffle and had to guess the "fill limit" first time at the pumps. Guessed wrong and bike ran poorly until a couple of tenths of fuel was used.

Here is my question. The roll over valve seems to be a one way check valve that will only close when the bike is in some position you'd rather not see it in, like upside down. I disconnected the hose from the gas tank cap and blew into it and air passed thru with just a bit of resistance. Am I correct in how the valve is functioning? Has anyone bypassed or disconnected the valve and just run the over flow hose some place else?

Thanks in advance for any advice!

Roll over valve?

That's what it is called in the Yamaha Shop Manual. Normally the breather in the gas tank goes to this valve then from the bottom side of this valve a hose continues on to the charcoal canister and then a hose from the canister to the throttle body. The previous owner installed an after market exhaust and removed the canister. They reconnected the hose that went from the valve to the canister to the throttle body. I'm thinking that when the tank is full and a bit of gas sloshes into the breather tube it goes through the valve and right inro the throttle body and floods the engine.

So there should be a hole somewhere along this baffle inside the tank? I've never noticed anything. Wouldn't it be way to easy for the gas to get into that hole simply be driving on a bumpy road? What about serious offroading, then? Gasoline would be all over the place in there.

There is a hose attached to a tube at the bottom of the gas tank on the front left area. This hose runs down to the roll over valve. I assume the tube at the bottom of the tank is routed internally up to somewhere above the baffle. This would create a breather for the tank and being above the baffle it would be away from foaming and sloshing gas unless the tank is filled above the baffle. These are my best guesses. Again I'm just trying to find out if anyone has deconnected the valve and run the hose to someplace other then the throttle body.

The PO f'ed up.

The vent hose is not suposed to be hooked to the throttle body without a carcoal can to catch the gas before it goes into the throttle body.

Your bike has a few things on it that only bikes sold in californa get.

On your IMS tank run the vent line with no valve in it at all from the gas cap to the hole in the steering stem like most all dirt bikes.

Thank you Biglake. You have suggested exactly what I have done as all my dirt bikes from long ago where set up like this. The preious owner removed some of the California emissions devices like the cannister. He must have figured the connection to the throttle body should be maintained once the cannister was gone. I can assure anyone who removes the charcoal cannister that reconnecting the overflow back onto the throttle body is a bad idea.