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MG Midget and Sprite Technical - remove fuel evaporative loss control system

When I got my car some of the evaporative loss control system had been removed. I have 1974.

Here is what mine looks like now:
The charcoal canister is removed from the engine area.
There is a hose coming from the valve cover that just vents it out the bottom of the car near the rear part of the right side engine area. My valve cover cap (where you pour the oil in) is a plastic vented one (there is a little hole in it).

There is a hose that comes from the air oil separator and goes to both carburetors.

In the trunk there is a vent line that comes out of the top of the tank and goes to a "separator tank" that is bolted to the side of the inside of the trunk. Another line comes from the other side of the separator tank. This line goes back to the trunk floor and is fed through to the underside of the car. A line continues on the bottom of the car towards the front of the car but it ends near the place where the brake line goes through the tunnel. It is apparently disconnected from a line that used to go to the front of the car. In the Haynes manual (no drawings of this in my workshop manual) there is a complete diagram. There is of course also a fuel line.

My understanding is that the vent line coming into the trunk which enters the separator tank was supposed to vent vapor from the carbon canister but now it is venting from the bottom of the car.

The two lines inside of my trunk need to be replaced (the ones that go to the separator tank). During autocross racing last weekend I was seeping some fuel in the trunk.

How should I fix or re-design my tank venting system so that I can go around corners fast without sloshing fuel.

Option #1:
replace the two old fuel lines inside of the trunk and hope that no fuel gets past the separator when it sloshes.

Option #2:
cap off the vent line in the top of the trunk and somehow turn my fuel cap into a vented cap (I am assuming that it is not already a vented cap). I am thinking that if I do this I still might slosh some fuel out the cap.

Option #3:
Remove my new fuel tank and instead install a fuel cell in the trunk (baffled by foam so fuel won't slosh, won't leak out the vent if the car turns upside down). I might do this eventually if my car actually turns into a race car but I would rather do #1 or #2 for now if it is safe.

Option #4:
Restore the complete smog/vapor system that the car came with back to the original design (really don't want to do that).

Thanks for your suggestions,

Rebecca
R Harvey

Sorry, my car is a 1973.
Rebecca
R Harvey

option #1 ought to work, as the vapor separator is intended to do just that. You could then vent the line that would have gone forward to the charcoal canister up high, say, attach it to the panel in front of the boot lid hinges. But do realize that this is an open line to the fuel tank (never drive with the hood/top up, ever, with this scenario). And you should restrict the opening with an orifice 3/64" diameter (the diameter, if I recall correctly, of the vent hole in the vented fuel cap.

or you could go with option #2, though, if you are racing, a fuel cell is wiser than #2, because some will still leak out the cap hole.

I prefer to use the vapor recovery system/keep it intact because of how well it captures the hydrocarbons the car will release when just sitting around, but I do understand why for racing your priorities are different.



Norm
Norm Kerr

Is my stock cap vented? I was assumging that it is not a vented cap and that if I just cap off the line from the tank to the vapor system that the tank won't vent. If the stock cap is vented (or I can get a cap for one of the older models) then I can definately do option #2.

If I end up getting realy into racing I will just install a fuel cell. Right now I am thinking about this summer.

However,
If I do #1 but let the fuel vent up through the vapor separator and then out the trunk I would think that would be safer than letting it vent in the trunk (fuel vapor in a confined area makes me nervous) but the separator might prevent fuel from sloshing out the vent during autocross. If I vent it out the bottom of the car on the right side where it exits the trunk then I would think that it would be like a lot of cars that have a vent/overflow tube (some of my other old cars have that).

Thanks for your comments.
Rebecca

R Harvey

Option #1 is my vote.

As Norm states bring the opening to a reasonable location and restrict. My 1979 midget vapor line (similar to yours, with separator) terminates in the gap between the front fender body panels, left side, (safe from flame-type incidents) thru the 1/4" fixed stock aluminium vapor line, thence into fuel line, past the fuse box, then restricted with steel wool stuffed in the line. The steel wool slows down the evaporation (exposure) to atmosphere, without restricting so much to cause vacuum in fuel tank, i.e. I get no suction noise when removing the (non-vented) gas cap after a run.
Richard Reeves

Option #5

I would restore the evaporative loss system to its original state but leave the air injection system, which is entirely separate, removed.

I had the lines to the separator in the trunk of my 1971 replaced as these crack and leak. Then you would only need to change the oil filler cap to the unvented type and obtain a charcoal canister from either Moss or a wrecking yard.

The 1971 absorbed vapors from the fuel tank only while the 1974 also took vapors from the carb overflow vents.

The system should in no way affect engine output, unlike the air pump for the emission control that takes some amount of power to turn.
Glenn Mallory

oops, sorry, I should have been more clear about a vented gas cap. You are correct, your vehicle came with a sealed cap, so plugging that hose would cause vacuum lock unless a breather hole was also added somewhere.
Norm Kerr

Rebecca. The best option is to install the proper charcoal canister and hook up the line which runs from the vapor separator and the line from the valve cover to it.

Your non-vented fuel cap requires that there be some form of air intake into the fuel tank if you are to prevent building up of a vacuum inside the tank. Thus, the line from the tank where it goes into a vapor separator (called an expansion tank in my diagram), then, forwards to the charcoal canister in the engine compartment. The charcoal canister is open at the bottom with a layer of fiberglass mat and activated charcoal on top of that. There should be the line from the fuel tank, a line from the overflow pipes of the carbs, and a line from the valve cover connected to the canister. This is provides air to both the fuel tank and the engine while controlling the fumes from the carb overflows. (Your current hose, perhaps without a filter on it, could be dragging unfiltered air into the valve train area, then, down into the crankcase.

The charcoal canister serves a quite useful purpose, does not take anything away from the power of the engine, and keeps fuel vapors out of the atmosphere. There is nothing bad about the system and a lot of things good about the system. I would recommend that you restore it.

Bob and Gil Schaulin (602) 415-1846, in Arizona can supply a charcoal canister if you cannot find one locally. They are fully rebuildable using the fiberglass mat and activated charcoal available in pet stores for aquarium filter use.

Les
Les Bengtson

This thread was discussed between 05/07/2010 and 06/07/2010

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