Tank venting

[AlanH]

I would like to pick up on what Richard said in a previous post.

I have had the front carb off my latest 1850. I left it overnight only to find a strong smell of petrol in the garage. When I looked petrol was spewing out of the pipe that goes to the float bowl.

I took the fuel cap off, there was a large rush of air and the flow stopped.

The cap was was the locking type so I assume that, as Richard said, the tank vents through the cap and my one was air tight.

I'm not sure how the tank venting works, if the tank breather pipe just connects to the filler tube then what use is it?

I have an original that I can use for now but I would like a locking one so I wondered if it possible to vent the one I have, perhaps by drilling a small hole. If not does anybody know of a supplier of vented caps?

[tony g]

The pipe that connects to the filler pipe is only for filling purposes. It stops the petrol backing up and clicking the pump off, so only works when filler cap is off. Locking venting caps should be available so worth a search. Was yours warm in the garage? Seems odd to have pressure in there as opposed to slight vacuum..

Tony

[AlanH]

Was yours warm in the garage? Seems odd to have pressure in there as opposed to slight vacuum..

The garage is attached to the house so it is quite warm.

I did notice a slight intake of air when I took the cap off to fill the tank so I have assumed that the cap is not vented and vapours have created pressure in the tank forcing the fuel out of the pipe

[Richard the old one]

I recently attempted to purchase a new locking petrol cap from Moss but it turns out that our petrol pipe / cap is not a common size that they hold.

What I have done in the past is cut a slot across the rubber seal in the cap. I believe the MoT man should check the seal but if he is knowledgeable he should know that it is needed to let air into the tank as petrol is drawn out.

[RJF_70]

I too have this with my 1500 auto Dolly, always whooshes when cap removed, and when working on handbrake recently could hear a very slight hiss, remove cap and relocate and it stops. It too has a locking cap. Have tried making sure the vent is clear, may try like Richard says and cut a slot in rubber seal.
Cheers Rich

[tony g]

If you look at the standard cap, under the seal face there is a slot in the cap itself. The rubber covers most of it so its not obvious at first. If you can remove the rubber seal maybe a bit of filing or dremel to create a little gap that can allow air past it may be the solution. Gap doesnt need to be very big it only needs to allow air in at the rate the fuel is leaving.

Tony

[Triumph1300]

Also, there should be a copper washer under the seal

[tony g]

Yes good point about the copper washer Bruce. It stops the rubber squishing into the slot and closing it off

Tony

[xvivalve]

I have a limited number of second hand tried and tested locking caps