GAs pouring out of tank vent

I posted this about one month ago in regards to my 2000 YZ426, I have gas pouring out of the vent hose from the gas cap while riding. I have replaced the gas cap, vent hose and even tried one of the $15 white bros. short vents with the gold cap. As soon as I begin riding, whether the tank is almost empty or full, gas starts bubbling up the vent hose and starts pouring out. Its literally pouring out.

Makes no sense. I accidentally left the vent plugged(which is how I am able to keep riding, and the next day in the garage the tank looked like a crushed beer can, completely sucked the sides in. What am I missing here?



I am totally confused here. Let me get this right, whether your tank is full or low, gas leaks or pours out of the vent hose? AND if you plug it up the bike continues to run just fine? For any extended period of time? But when you accidentally left it plugged overnight, the tank was collapsed the next morning?

(1) For the tank to collapse, the check valve in the vent tube would have to be installed backwards or non functional. Or if it was very hot while riding and then the night cooled down drastically and rapidly with a clogged vent.

Have you tried removing the gas cap while it is running and place your hand over the tank, is it building pressure or vacuum? It wouldnt run if it was pumping into the tank!

Also those little vents made by (insert brand name here) bleed a bit of mist if the hose is under about 6" on Yamaha's for some reason. The instructions even tell you to leave the hose long on Yammies, Mine isnt and it seeps/leaks but so slight it isnt a concern.

You are right side up arent you? I see your address is Nebraska and that was in the US not Australia.

Yes you are correct, once I begin riding it pours out, tank full or empty. The check valve is of course pointing correctly towards the tank. When I am riding, I leave the cap somewhat loose and every once in awhile open it and yes there is a vacuum created. Bike runs fine. It is nearly 100 degrees here since this started occurring. I forgot and left it tight in the garage when the tank imploded....I blew it back out and left it sit for a day and it popped right back to normal. This tells me it is not vented at all.

This tells me it is not vented at all.

Gas coming out of the tube? That seems vented to me. The valve should let air into the tank and keep the gas from escaping. It sure sounds like yours is backwards.

Personally as an experiment I would take the valve off and notice how the symptoms change. Even if you put it valve on correctly it is possible the label is wrong on it...


Have you tried running no valve at all, just the hose? A few of us here only use a hose, no valve.

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