Venting a petrol tank

[scatman]

Is it possible to get a venting fuel cap for mk2 scirocco? Also where abouts is the venting pipe on a 89 fuel tank? Reason I ask is, is that my tank isn't venting properly. With the fuel cap on, it will randomly judder and cut out on longer trips at higher speeds (above 50). With the fuel cap it, it sits happily at 80 for hours. I've blown both lines on the gravity valve and they aren't blocked. The gravity valve seems to be working (though it's a sealed unit and I can't really Tell). there is small pipe behind the fuel tank with a rubber boot on it. Ive tried blowing through this,but it's blocked. could this be my issue?

[james butler]

the main breather is behind a plastic cover that sits in the wheel rear arch the same side as the filler neck.
the breather goes from the top of the fuel tank to a device (roll over gravity device that allows venting action unless the car is rolled over i believe) close to the filler neck then returns back down the same way to the breather opening that sits just behind the beam axle in front of the fuel tank.
so yes you should be able to blow through it.