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MG MGB Technical - vapour separator

O.K. I went through the archives and solved my mystery of why I have two hoses in my boot. Now, I have a 70 B, vented gas tank, but no vapour separator. If I was to close off the tank vent, and use a vented gas cap, would this be alright? What about where the two hoses from the fuel pump enter the boot, will these send gas vapours into the boot? What should I do about those? Or should I just replace the valve? If so, how do the hoses hook up?
I do not have the charcoal canister in the engine compartment. BTW, the engine is 18GH.

Thanks for all the help. The people on this BBS are the best!!!

Ken
70 B
Ken Harris

Technically, I think you'd be OK in closing off the
tank vent and use a vented cap, but this defeats
part of the vapor recovery system routed to the
charcoal canister (you also must plug the hose barb on the canister which leads to the tank).
Note that there's no performance gain in doing
this, and you'd only be adding pollutants into
your (our) enviornment.

I would do this only as a temporary stop gap until
a proper separator bottle can be found.

The small vinyl tubing should each have a plastic
"T" fitting to prevent them from sliding back out
of the trunk. They are breathers from the fuel
pump. One hose is from the points cap on the
pump. The other hose is from the pump body.
As the pump is doing it's "thing" - the pump
diaphragm also displaces air (back & forth).
The breather hoses eliminate any air pressure
which the diaphragm would otherwise must work
against. The tubes are mounted up in the trunk
to minimize any road dirt or water from entering
the pump (and leaving you stranded). Unless
there's something very seriously awry with the
pump itself, there's little chance of fuel vapors
entering the trunk.
Daniel Wong

Ken. I do not think you can fit a vented cap without replacing the filler neck. At least that is my reading of the Moss catalog (page 28, illustrations 1 and 3).

The vapor seperation tank mounts on the right inner fender. It is hooked to a vent line from the tank and a line going forwards to the charcoal cannister. When the system is not hooked up, correctly, two things will happen. If the lines are not connected in the trunk area, there will be a build up of gas fumes in the trunk which, when driving, will be pulled into the passanger compartment. When the lines are hooked up in the trunk, but there is no charcoal canister to absorb the fumes, the gas fumes will build up in the engine compartment. Neither of these is a very good idea. As Daniel notes, when the fumes are vented to the atmosphere, they pollute the air. When they are vented properly, they allow little, if any, of the fumes to escape into the atmosphere. This system robs the engine of no power and requires little maintenance over the years.

My advice would be to install the vapor seperator and install and hook up a charcoal cannister in the engine compartment. Barring that, you will probably have to replace your filler neck with a 62-69 model and add a vented cap. You can get used parts, of good quality, from Bob Schaulin at gbmg@aol.com if you cannot find them locally. Les
Les Bengtson

Ken; If you do not plan to replace the complete vapor system it's best to fix it as Les describes. Get the early type filler tube and a vented cap. The early filler tube has internal cap lugs and the vapor system uses a non vented cap with external lugs on the filler tube. Remove the hose that is attached to the gas tank vent tube and put a cap on it.

You can also try this and see if you get any gas smell in the boot. Remove the hose that is attached to the floor connector and connect the hose from the tank vent tube to the floor connector. Under the car remove the tube running from the floor connector to the engine compartment. Fabricate a vent tube from the floor connector toward the rear of the car. If this works you will not neeed to replace the cap or the filler tube.

As Daniel and Les mentioned it's best to replace the vapor system and help keep the air a little cleaner.

FWIW, Clifton
Clifton Gordon

Some confusion here for me. A 1970 B with a 18GH engine is a Federal spec car, (same for Canadian market) and did not come with the evaporative loss system as new. The 1970 B with a 18GJ engine (US California spec) did have the vapor cannister. You have the extra pipe (metal) coming from the fuel tank sending unit? Right hand side of the tank. As has been mentioned, the caps and filler necks are different as well. Perhaps some mix and match has gone on in the cars past. The lines from the fuel pump to the T connector are normal. Is there a seperation/expansion tank mounted in the boot? Right hand side. Both type engines have a tube coming out of the valve cover towards the rear pointing at the distributer side of the engine. My car a 1970 18GH Federal spec model has this capped off with a rubber cap and a two wire clamp. It looks as if it was an after thought, but is actually factory installed. The 1970 18GJ engines had a purge line from the carbon cannister connected here. Is your oil fill cap vented or non vented? Again 18GH vented, 18GJ non vented. My build date is 06/70 as shown on the data plate drivers side door jamb.

HTH

Ron
Ron Smith

Ron, no i don't have the separation tank mounted in the trunk. That is what i'm trying to figure out, as i cannot find mention of it in a haynes manual or MOSS catalogues.

Would i take a line from the T, to the separator, and a line from the separator into the vent hole in the gas tank (just behind the filler tube)?

I do have the same tube al;so capped with a stopper and clampo. Good to know this is what it is supposed to look like, i thought it was done by the PO.

Ken
Ken Harris

The Haynes manual is not bad, but does not go into detail on alot of the little things. Page 91 figure 3.41 is pretty close, but is a later RB car. It shows the basic hookup, #18 is the seperator tank mounted in the boot. If I had to guess you have a car that did not come with the evaporative controls. Perhaps it had the tank replaced with a later style. If it were me, I would use a vented cap and cap off the second pipe from the gas tank. It will not allow any more gas vapor to escape than any other car without the evaporative control. (all MG's 62-late 70)The T connector in the boot is only for the fuel pump and has nothing to do with the emmissions control. One small tube from the point cap of the pump, the other goes to the fuel pump body on the dry side of the diaphram. Neither has any vapor or fuel involved. The Moss catalog does not really show the differenace in the tanks, the VB catalog does. 1970 was one of those "change years" for emissions.

Safety Fast

Ron
RJS Smith

Ken; The vapor separator and associated parts are shown on page 21 of the current Moss catalog. Item 76 near the top right of the page. It is listed as NA. Clifton
Clifton Gordon

Thanks everybody for the help. mystery finally solved. I thought htat the line from the fuel pump had to go somewhere after the trunk, but now I know different.

Ken
Ken Harris

This thread was discussed between 04/02/2004 and 05/02/2004

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