Weber Dismantle-Rebuild.

There is an old saying, that working on the weber DCOE carby is a black art requiring techniques and skills known only to the specialists who self promote their technical expertise and rebuild services.

In reality, the Weber DCOE is nothing more than a complex pressure die casting which contains many finely calibrated metering jets which are intersected and integrated with several internal galleries and cross drilling’s which deliver and feed the fuel into the various circuits on demand.

The Weber carburettor is a very precise high performance instrument, if it isn’t properly maintained, serviced, and cared for, then you cant expect the Weber to deliver the performance they are well known for.

So, if your Weber requires some well deserved TLC, then your question might be….

Should I DIY Rebuild The Weber or Not?

The answer is simple –
If you are mechanically competent – Have a good understanding of the Weber DCOE – You have the proper tools… then the DIY route could be for you.

But you might want to do some in depth reading on the subject before you attempt to do your own carby rebuild work.

If you take a search around the web regarding Weber Carburettors, there will be pictures of carbs that are totally corroded and knackered, and people will attempt to rebuild them, when the next best place for most of them is probably the bin.

The metal that the Weber die cast body is a zinc based aluminium alloy, it is quite strong and robust when new, but if the overall corrosion and metal decay is really bad and eaten away, then you might want to question if they can be rebuilt successfully, and if they will perform as they should.

As always, to dismantle automotive parts you need tools, not always expensive tools. The weber can be mostly dismantled with a decent screw driver. If all of the screws and jets can be easily removed, your almost on the home run, but if the old corrosion curse has been present for any length of time, then a good soaking in a strong penetrant of some kind will be required, followed by hydra blast cleaning.

The dismantling job will could also come to a screaming halt at the point where the throttle spindles and butterflies need to be removed. On the early Weber 40DCOE there are brass covers that hold a short compression spring, which presses on a leather seal, which is supposed to protect the ball bearings… but in all honesty, they don’t… but if there is any sign of slop, or a notchy feel to the bearings causing excessive movement in the throttle shaft, the bearings will be worn out and require replacement.

The bearings are only a few bucks each, four bearings are required, your local bearing shop will be able to supply them, but the new bearings will be fully sealed, which is far superior to the old open style of ball bearings.

As anybody can see from the picture above, the old ball bearing on the left is well and truly beyond its use by date, which is to be expected after having being rolled backwards and forwards with throttle movement over the past fifty years.

New throttle spindle bearings restore the weber throttle to a silky smooth operation with no spindle slop, which will improve throttle response, making them easier to balance, set proper idle. Well balanced Webers are easier to tune.

The original leather seals deteriorate over time, and they don’t protect the bearings from grit and water ingress, so the bearings just suffer from constant wear and become very loose, and sometimes have a notchy feel.

The little brass protective cap (Above) can be a pain to remove with out damage if you don’t have the correct tool. The writer decided to carefully measure the holes in the cap, and make a special tool,with pins that engage in the holes, which enabled the brass cap to be twisted out and allowed access to remove the bearings.

To keep things in order, and so you know which parts are going back where they came from, make sure to mark the spindle and carb body with a yellow paint marker… something that wont rub off.

Also, make sure to mark the butterfly plates LH and RH and put tiny reference dots with a sharp centre punch on the spindle and butterfly. Once the ID work is completed the throttle plate screws can be undone. The screws are swaged on the end of the thread to prevent them vibrating loose, they can be carefully unscrewed with some effort on a proper fitting screw driver. When replacing the screws, a medium strength thread locking loktite should be applied.

The throttle spindles and butterfly plates are fiddly to get them to settle back into their original position…and a word of warning, spend the time to get this right, otherwise the Webers will not work properly. Check also that the plates are aligned to each other and the spindle has not been twisted.

When the spindles and throttle plates have been bedded in correctly, the throttle will open and close with a snapping sound, they should not bind or foul at any time during the opening or closing.

Removing and replacing the throttle spindles and butterflies will provide the most frustration with the Weber dismantle job… and probably the reason why most will send the job to the weber guru… but as we said at the beginning, you can do it your self, but be prepared to spend about three to four hours on each Weber.

There are a few videos on you tube which provide good instructional detail… but mostly, all you need is mechanical common sense, and a good instruction manual for the particular type of Weber that you have.

Be very particular about cleanliness, if the carbs and jets need a lot of cleaning work, then perhaps a sonic cleaner should be considered. With carburettors, cleanliness is godliness.

Custom Machined Weber Chokes.

The rebuilt twin Weber carbs will be feeding a 1700cc Lotus Twin Cam, so the decision was made to go up another size in the chokes. The photo above shows a new set of custom machined and milled 34mm chokes.

Weber choke sizes graduate in 2mm steps, IE, 30, 32, 34, etc, but if you have the facilities to machine, there is no reason to say that you could not produce a 32.5 or a 33mm choke, if it was called for during the dyno tuning work.

Weber carbs are very flexible when it comes to altering any of the jet, air correctors, emulsion tubes, they are all supposed to work in harmony, and a good dyno operator will get them all spot on, and there’s no denying that weber’s are a total delight to drive with when they are tuned to perfection. And you cant deny that the clucking sound they make is simply beautiful.

In your quest to build a highly tuned lotus twin cam engine, spend time on the Weber’s to make the experience even better, don’t just take it as a given that all is well inside of your weber 40DCOE carburettors… Because they may not be as good as you think they are.

Elantrikbits Australia, sharing useful information to other Lotus elan owners across the globe.