V7 Classic Fuel Tank Pressurisation

I’m new to the V7 Classic. My bike appears to be pressurising the fuel tank after a ride - fuel seeps out through the filler key-hole. Releasing the cap shows the tank is pressurised. Curiously, replacing the cap and locking it, the tank will again re-pressurise without the bike having been run, or even the ignition “on” (activating the pump).

I have yet to find the tank overflow from the filler neck - I assume there is an air vent to the tank, unless it draws air in via the cap. From reading the posts on Guzzitec it seems that US spec bikes have two vent pipes: one via a carbon canister (to “collect” fumes) and another with a one-way valve to allow air in to the tank. UK spec bikes apparently have but one vent pipe.

Several possibilities occur to me. The fuel lines stay pressurised after switch off: perhaps the pump seals are failing. It was fairly cold when out riding today (3 to 5 degrees C) and the bikes now lives in the Bunker (ambient temperature 16 to 18 degrees C) - is fuel expansion the cause? Or is it simply a blocked fuel tank vent? (with or without a one-way check valve)

I suspect someone with a UK spec bike will have experienced similar and know what the cause/cure is. The bike’s a delight to ride - I need to familiarise myself with the various gubbins. Can someone point me in the right direction, please?greybeard622012-12-16 18:15:52

Sounds as if the overflow/vent is blocked. if you have a plastic tank, then the vent goes through the bottom via an aluminium ferrule which has a very small hole. It is possible to drill this hole out very carefully. Baldrick at Corsa does this as part of the PDI as it is so prone to blocking.

Thanks for that. I’ve spoken with said Baldrick - for the benefit of others whose plastic V7 tanks take to pressurising, he tells me the ferrule in the bottom left of the tank that is the actual vent pipe connector, simply unscrews from the tank. The tiny hole through it he suggests be carefully drilled out to 3 or 3.5 mm before being refitted to the tank and compressed air gently blown up (to ensure the line to the filler cap is free) and down the pipe, before reconnecting.

Lifted the tank on my V7 Classic today. The vent ferrule is non-anodised aluminium and was caked in oxide - taking the pipe off, the ferrule was blocked with a plug of compacted oxide and a line full of water above it (obviously from the drain in the filler cap surround). I suspect the fuel vapour pressure (heat from the engine after riding) has consolidated the blockage. Having cleared the duct from tank top to ferrule (pipe cleaner at the bottom, air-line at the top) I’ve dribbled ACF 50 to coat the inside of the aluminium ferrule and when dry, discourage the production of white oxide. The tank doesn’t pressurise now.

Good result, thanks for sharing.Regards,John