It seems like the gas cap on my 400ex is leaking fuel... With a full tank or even down to about half a tank, when I'm riding the trails I started to notice fuel on the plastics around the gas cap, like the fuel is sloshing up and out around the cap. I had the cap really tight so I'm wondering how fuel is coming out around the cap?? I really don't think it was coming from the vent tube, because the vent tube is connected tight on top of the cap and the tube runs down inside the steering stem, so even if fuel was coming out of the vent tube it should run down inside the steering stem and not get all over the plastics around the gas cap. Is it normal for these 400ex's to leak a little fuel around the cap when its got a full tank?

 

Nope, thats not normal. The fuel tank may be damaged or like you said the cap.