Fuel Tank Vacuum

[pwarren]

Hi, I'm new to this so please bare with me.

I was out last weekend in my Series 1 with a full tank full of fuel and it conked out after about 20 miles. Electrics and such all ok but no go. After resting by the side of the motorway for a few minutes she started up again no problem. Another 5 miles down the road and she conked out again. When going through a more thorough investigation process I opened the fuel cap and there was a great rush of air into the tank. After that she started up fine. -

Obviously a vacuum had been created in the fuel tank that was too much for the pump to overcome and the engine became starved of fuel so it conked out.

Inspecting the original fuel cap I noted that it has no vent hole, so thereafter I left the fuel cap loose and all was OK.

So my question is.... Where does the fuel tank vent to the open air? I know there is a vent pipe on the tank, but I understand that that is to allow air to be expelled as the tank is filled. With the fuel cap on this circuit is closed to the open air. So, how does air get in to replace fuel used?

Any ideas?

[christopher storey]

It sounds to me as though your filler vent pipe has a kink in it . AFAIK it should not act as a one way valve , and should allow air in and out

[288gto]

It sounds to me as though your filler vent pipe has a kink in it . AFAIK it should not act as a one way valve , and should allow air in and out

I might be wrong Chris but I always thought the only thing venting the tank allowing air in or out once the cap is on, is the tiny hole in the filler cap itself? The tube from the tank to the side of the filler neck allows air out when you are filling the tank so you don't get fuel splashing back on you. To the OP, have you only just started to experience this problem or have you changed the fuel cap recently?


Simon

[tinworm]

I think the caps with no hole are S2 US models with the carbon filter/trap. All S1 (ITHINK) have the small 1/32" hole.

Barrie

[pwarren]

Thanks for the feedback, but I don't think that the vent pipe from the top of the tank to the side of the large filler tube is the issue as it is actually a closed loop within the tank system once the filler cap is on. I understood that the venting pipe is two way, but is there to allow air out of the tank as you are filling it up.

My problem is, with the filler cap on, trying to get air into the tank to replace fuel as it is used by the engine. At the moment no air is getting into the closed system, so a vacuum is formed as the fuel is consumed. I guess I will just have to drill a small hole in the filler cap?

[tinworm]

pwarren see my above post.

Barrie

[lopena]

This is what you need:




Alan
N.J.

[pwarren]

Thanks guys.

Have just drilled the hole. Good motering