Weber Carburettors – How To Recondition Worn Manifold Flanges.

Most original Weber’s fitted to the original twin cam lotus are now about fifty years old, and as with most old things, they are tired and worn.  If you closely examine the manifold flange faces on any old Weber,  there is a very good chance that noticeable wear and abrasion will have taken place.

Sometimes unexplained engine running problems can be traced back to the flange faces of the carbs, as you could imagine if there is bad wear & tear on the flange surface that is designed to be sealed with an “O” ring, a smooth well machined surface is required for the O ring to create the seal, just a small gap could allow unwanted air to pass by the “O” ring which could cause the mixture to lean out, a problem that is not always easy to trace back to the Weber’s

So What’s The Fix?
Simple, remove the carbs from the engine, clean them externally, carry out a partial dismantle & strip of most parts but not all. What we are going to do is to mount the Weber carb body onto a lathe face plate and carefully face, or machine 001.5 – 000.20 thou from the inner manifold flange face to remove any possible wear marks,  grooves, dents & or irregularities, the pictures below explain the procedure.

If you don’t have a lathe, you may have to take the carburetors to a machine shop and explain what you want done, but you will have far more control over things if you can do this job your self, as it is just a basic set up and machining operation. NOTE: Both carbs must have the same amount of metal removed, otherwise one body will be a slightly different in length or dimension.

We are not about to detail the setting up of the lathe nor the machining operation, if you already own a lathe you will understand what is required to do the job, otherwise you may have to locate a machine shop to do the work, or perhaps an acquaintance who can do the work in a home workshop.

Notice the wear marks on the flange, look closely at the picture above, the grooves and wear are quite evident, even the  lead plug that seals the cross drilled gallery reveals a depression below the metal flange surface, the indicated wear on the face of the flange was a good enough reason to go ahead with the machining and reconditioning of the “O” ring sealing faces of the Weber carbs.

The Weber does not need to be totally dismantled, but after the machining is complete, make sure to wash and blow out with compressed air before rebuilding again. The face plate is placed on the work bench during the set up and clamping of the Weber, use at least three clamps and make sure even pressure is applied to each clamp, once the carb is set, attach the face plate assembly to the lathe, then rotate by hand to make sure nothing snags or hits on the lathe bed or any other part of the lathe, once you are satisfied, set the lathe to a slow spindle speed, and carefully begin the machining operation using a sharp cutting tool, the metal is die cast aluminium and machines extremely well, remove the smallest amount of metal required to bring the flange face back to as new condition again.

When the flange faces of both carb’s  have been machined and reconditioned, it is time to begin to clean up and rebuild the Webers. DO NOT leave any swarf in the carbs anywhere, make sure they are totally clean before reassembly.

Note that “O” rings can also wear and abrade which can create air leaks.

Before rebuilding the Weber’s, it is time to also acquire a new set of “O” rings,  as you would realise” O” rings can also wear and abrade over time, the “O” ring in the picture above is an old one, and wear and tear is visible.

Handy Hint For Cleaning Weber Carbs.
After a total dismantle, soak Webers in a mixture of carby cleaner and a strong de-greaser, (Not the alkaline type) then taking a short length of gal tie wire, fasten through the flange bolt holes. Place some boiling water in a plastic bucket, then add a very strong mixture of industrial strength detergent and then proceed to plunge the carbs several times up and down in the hot water, remove, let drain for a minute, then blow dry with compressed air,  make sure that every hole and orifice in the carbs is blown clear of water, to make sure that all traces of water has been removed fill a small container with methylated spirits, and immerse the carbs, any water will be dispersed.

You don’t have to drive or own a lotus elan to use the techniques and methods above to recondition Weber carburetors. Just work carefully and think about what you are doing.

Footnote: Since this article was written, vapor blast and or wet blasting has become the preferred process of cleaning aluminium items such as carburetor bodies etc.