MOT fail - excessive fumes from petrol tank vent.

[WotnoV8]

My S1 just failed it’s test as a small drop of fuel (“size of 50p”) came out of tank vent pipe when car was jacked up. Tried explaining the tank is vented direct to atmosphere so was prob just a bit of condensed vapour from where car has been standing outside in the sunshine. He was erring on side of caution and admitted not knowing anything about these cars (Unfortunately the “old boy” who used to do the mots and understood old cars has recently retired).
So my question is has anyone fitted a charcoal canister/catch tank to their petrol tank vent at all?

The petrol tank isn’t full so that’s not the problem.

[steveo3002]

id be tempted to put a bolt in it , retest then back to normal

[WotnoV8]

That was my first thought

[GreenV8S]

Can you reproduce the problem? I've never seen petrol condense except in a closed container and it doesn't seem like a particular likely explanation. It may be you're seeing petrol coming past the filler cap and out the drain, in which case you could be losing petrol on every corner.

[WotnoV8]

Only just over a quarter tank so don’t expect it to reach filler cap. If it did the first route out is the vent which is on the filler neck.

[v8s4me]

Put a bolt in the tube as above or disconnect the pipe at the filler end and put a temporary pipe leading to a container on the boot. Or find another tester.

[WotnoV8]

I think thats prob the way to go with this.
It may be a sign of the times as MOT testers get younger (or is it me getting older?) they just are not used to old school emissions (non)control systems.
Will still investigate more anyway and will change the filler cap gasket while I’m at it just in case.
Have to say I’ve never noticed any fuel under the car at all and I get under it fairly often to potter around. (Have a 4 post lift so its quick to do).
Cheers

[phillpot]

has the pipe got a 'pigtail' loop in it?

[WotnoV8]

No, but made up something similar earlier, and hopefully fit it tomorrow.

[WotnoV8]

After fitting a “pigtail/Ubend” section of kunifer into vent line the car passed it’s retest yesterday.
Now planning on ditching that and putting an inline vent valve/rollover valve above the vent take off as a neater solution. (See Car Builder Solutions catalogue). This will vent if tank pressure rises and also open if the pressure in tank drops.

(PS I tried to replicate the “petrol drip” with the original set up but vent line stayed dry, so that remains a mystery).

Edited by WotnoV8 on Wednesday 7th April 16:06