Our MGB's use a charcoal canister to trap gas fumes from the gas tank
and the carburetor float bowls. The trapped fumes are then sucked
through the valve cover, through the crankcase and out the vent on the
tappet cover on the side of the engine by carb vacuum. This system
uses absolutely no energy to operate so it should be left functional
when you remove the air pump and other emission equipment. Over
time, the filters and charcoal degrades
to the point of being sucked into the crankcase. One thing you do
not want in your crankcase is bits of charcoal.
Repairing the charcoal canister is not all that hard. The first
thing you have to do is to open it up and clean out all the old
contents. The bottom unscrews to expose the retainer. The
retainer is the piece that looks like a ring divided into
Notice the ring has six tabs in it that fit in matching slots in the
bottom of the canister. These have to be carefully depressed so
the retainer will be released. After the retainer is removed, you
will find a filter made of plastic gauze. Pull this out and
examine it. If it is in decent condition set it aside for re-use.
Under it you will find the old charcoal. It looks like black
pellets. Dump these in the trash. They are not
re-useable. Under the charcoal you will find another filter like
the first one and a steel mesh screen. If the screen is intact,
save it for re-use.
Next you will find a special washer and a spring. These should be
cleaned up for re-use also.
Okay, now you have it all out and in front of you. If the two
filters are not re-useable, you can make replacements from filter
paper. I had access to some filter paper so I cit several
3-1/2" circles. Lacking this, you can use plain old coffee
filters. Look around for some large enough to cut the discs from
without leaving any holes. After you make your new filters, you
are ready to go back together with everything.
For charcoal, I used plain old aquarium filter charcoal that's available
from any store that sells aquarium supplies. You'll need about
8-ounces of charcoal You can wash it first, and dry it in your
When you are ready to reassemble your canister, start by placing the
spring and special washer in place in the bottom of the canister.
Next, install the steel mesh with either your old filter or your new,
homemade filter on top. My original filter was re-useable so I
used both the old and the new one.
Next comes the charcoal. Put about 8-ounces in. It should
fill the canister up to the point where the other filter and retaining
ring will just fit in place. It you overfill by a bit, it will not
matter as the spring will compress enough to keep pressure on
everything. You want the whole packed bed of charcoal held in
place by the spring.
On top of the charcoal goes your second filter and ten the
retainer. Be sure the retainer locks in place with its six tabs in
their matching slots. Now all that is left is to screw the bottom
back in place and reinstall the canister back in your car. and hook the
hoses back up.
Not so hard after all, was it?