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MG MGB Technical - Petrol tank vent

Just cleaned up the boot, painted, re wired, etc. But at the back (if you open the lid, far RH side) on the floor there are some tubes that come up, look like clear windshield washer fluid tubes, but don't seem to go any where or have anything to connect to. Now if this is the venting for the petrol tank, why vent into the boot ?
What a to do...
G.L Lodge

These are likely the vent tubes from the fuel pump. they normally come up in the boot just behind the passenger compartment on the right side with a "T" in each one.
John H

Thanks John.
I have a T piece, but again it just hangs there. Any problem just shortening the pipe so i can plug up the boot ?
G.L Lodge

The vent tube for the vent on the bottom of the coil housing needs to be routed to a high spot under the car or into the trunk. If the tubing from this vent is allowed to dangle down, there is a chance of it's sucking water into the coil housing of the pump if you splach water up under the car such as when driving through a puddle (I had to rework a pump for a customer where just such a thing happened - in Southern California of all places). The tube was originally routed into the trunk as an area that is relatively dry. It can also be routed into the battery box and clamped in there so it doesn't dangle. The vent tube on the end cover is not as critical as it has a check valve in it and does not draw air in at that point. Cheers - Dave
David DuBois

So if i was to carpet the boot i'd have to make a hole for the vent to go through. Having it go up through the battery box area sounds like a good idea, thanks

What a kerfuffle
G.L Lodge

>So if i was to carpet the boot i'd have to make a hole for the vent to go through.

No, just leave the 'T' in place under the carpet. It'll be fine there....
Rob Edwards

This ventilates the back of the diaphram on the fuel pump. If it were plugged the pump would have to push against a pressure every time it pulled petrol into the other side of the diaphram. Nice clean dry air whooshing back and forth is the ideal. Lead the tube up a little then have a down turn at the end, like a snorkel. You could duct it to the boot bulkhead behind the carpet.
Peter

Hi
I was helping to install a new fuel pump in a friends '73 B and I noticed a metal, pancake shaped box, about 5" diameter and approximately 1½" thick attached to the RHS wall of the trunk. The fuel line from the tank was connected on one side and continued out to the fuel pump on the other. Anybody have any idea what it is? I thought maybe some sort of filter, but it seems too large and permanent to be a filter. Could it be some sort of fuel vent?
Cheers
Ken
Ken Martin

Ken. Actually, the line goes forwards to the charcoal cannister and has nothing to do with the fuel pump. What you are describing is the vapor seperator which has a line from the tank to the seperator, then a line to a fitting near the battery box, then a line forwards to the charcoal cannister. It is the vent for the fuel tank and your friend's car should have a non-vented fuel cap.

Les
Les Bengtson

OK, please clear up two items concerning the Petrol tank vents in the trunk. My car is a 73 MGB.
1) Is there suppose to be one or two of the vents in the trunk?
2) Do the vents in the trunk connect to anything or are the ends of the "T" just suppose to be open to the air?
Thanks,

Robert Browning
Robert Browning

OK, let me add one more thing - and please know that my hands are all greasy as I type this...
I just went and crawled under my car to look at the fuel pump. The "T" vent coming from the trunk is not connected to anything. It is just hanging there in space. There is however a separate vent tube running from one end of the fuel pump that goes into a hole in the frame beside the fuel pump. I pulled it out and it was just pushed into the frame - through a rubber grommet - I assume for venting.
The vent on the other end of the fuel pump is plugged with a rubber cover.
Shold I attach the "T" vent in the trunk to this end of the fuel pump?
Also, can I - would it hurt - to connect both ends of the fuel pump to the smae vent tube - like the one running into the frame?
Thanks,
Robert
1973 MGB
Robert Browning

You are correct the line running into the frame is the diaphram vent, it is where it is supposed to be. From back of pump to theoretically clean air in the frame. It used to be a clear, roughly 5mm, plastic line, like the windscreen wiper water pump line. probably a manky yellow colour now.
Other vents/lines.
The filler neck to the petrol cap (obvious).
I mention this because below the filler neck, a little (a couple of inches) to the left, is a small, a few mm diameter(maybe 5), right angled pipe sticking up out of the tank/boot floor. Or a threaded vent to attach right angled pipe. This is the petrol vapour, antipolution vent line. A rubber petrol type line runs from this up to the bottom vent of Kens "pancake shaped box". This is located up behind the tail light, RHS. From the top vent on this vapor separator a rubber line goes down to another small pipe located on the floor of the boot under the vapour separator on the extreme RHS. If you then crawl under the car and look up just there, you should see a line (looking like the metal petrol line, but a little thinner) heading off towards the charcol canister up in the engine compartment. The idea is that any petrol vapour will condense in the separator and run down back into the tank. Anything else ends up being caught in the charcol filter. No polution.
Thats all the pipes there are.

However, your fuel tank may have been replaced with a new one. If this is the case then there is every chance that the new tank does not have the vent line next to the filler neck. Vented tanks are very expensive here. My new tank did not have a vent.
The options are to put a vent on the filler neck and conect the vapour line to that. This is what I did.
Some people simply drill a very small hole in the cap and make a "ventilated cap" as per the early mark 1's. Or they fit a mark 1 neck and cap. Either way they ignore the antipolution gear (or rip it out)
Peter

"all the pipes there are" inside the boot that is.
Obviously a single petrol line runs from the tank to the carbies, but this is located below and outside the boot, on the RHS of the petrol tank.
Peter

This thread was discussed between 14/04/2006 and 23/04/2006

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