question about little pipe connections fuel tank

[HG_S-type]

Hi,

Last week I noticed that the engine of my S-type was stuttering and runs irregular after about 10 minutes driving.
Switching to the other fuel tank helps a bit but after a few minutes the engine stutters again.
At home I looked at the fuel pumps and they seems ok.
But I noticed that on the left tank the hose on the two little pipe connections was loosed/broken.
I fixed that and the problem of stuttering seems solved after a test ride.
But I'm wondering now what the meaning is of these two little pipes? They are on both tanks and connected by a hose direct from one to the other.
Could that explained the irregular running of the engine when one them is broken?
Attached a picture of these ones.

S-type_fuel_tank.JPG (34.98 KiB) Viewed 2597 times

Thanks,

Harrie

[cass3958]

I have always assumed ( my mother always told me never to assume anything) that those pipes were air vents so you do not have to have an air vent hole in your fuel cap. As the fuel is drawn through the system by the fuel pumps if there is no air vent a vacuum is created in the tanks which will stop the fuel being picked up. When you ran your car did you try releasing the petrol cap and if you did was there a rush of air going into the tank?

I know when I rebuilt both my tanks I got a long flexible piece of steel rod which I pushed down these tubes to make sure they were cleaned out and free of obstructions. If some one has treated the insides on the tank with something like POR15 as I did but failed to clear the vents they could be blocked and causing a vacuum and the symptoms you have.

[HG_S-type]

Hi Rob,

Thanks for your response and your advice to clean those pipes with a flexible steel rod.
I will do that this to be sure that they aren't blocked.

Regards,

Harrie

[Glyn Ruck]

Those are all part of the tank breathing system. Those long loops of pipe are crucial to proper running ~ Don't ask me how I know - had the same problem. Follow Cass wise advice & keep the pipes clear & don't remove that long loop of breather pipe. (7)

tanks.jpg (84.58 KiB) Viewed 2592 times

[HG_S-type]

Hi Rob,

About your remark: "my mother always told me never to assume anything"

It's a good advice. Because one of my previous employers has in the 10 rules of the company:
- WE DON'T ASSUME: WE ASK QUESTIONS

Harrie

[HG_S-type]

Thanks Glyn for your response.
Appreciate it.

Regards,

Harrie

[NigelW]

I've always taken it that the pipe 7 is an early form of fuel vapour emissions control. Vapour from the tank travels up pipe 7 that is tucked up in the B pillar where it condenses and any petrol is returned to the tank via the filler neck and "cleaned" vapour exits via the rear steel pipe on the side of the tank to under the car. If the car is running rough the vent in the fuel filler could be blocked and the vapour control is running in reverse suckling air into the tank. Just ensure all pipes are clear and the tank cap hole is clear for everything to work as designed.

[Glyn Ruck]

I think you are correct Nigel.

[John Quilter]

An old speedometer cable might work well for ensuring there is no blockage in these small tubes.

And on another note. I just got round to cleaning the SU fuel pump points on four of my smaller British cars hopefully to ensure they do not get recalcitrant and leave me stranded. Removing the outer set of points (sometimes these are double points) gives good access to the inner set of points. A gentle cleaning with my Dremel tool did the job. Doesn't apply if you are using the electronic SU pump.