Weber 28/36 DDE Carburettor (Part 1) - Stripdown and Overhaul

Carb rebuild.......

My carburettor had looked a bit of a mess......

Dirty Carb - June 2015

There have been many different carbs fitted to Ds over the years - with variants according to  (or is that 'determining'?) power/ engine size and whether or not the model has hydraulic gear change. As a DX engined DS21, my car has a Weber 28/36 DDE. Manual gear change 21s of the period used the same carb but the 'A1' variant.  

Operation D.142-00 in Volume 1 of Manual 814 gives an overview of most of the carburettor variants used on the later five bearing engined cars. This includes Solex carburettors as well as Weber.

Carburettor removal instructions for bvh cars can be found in Operation DX.142-1 of Manual 518. An overview of the 28/36 DDE  - including jet sizes and other specifications - together with overhaul instructions can be found in Operation DX.142-3.

Another useful resource is the exploded diagrams of all the carburettor parts. You can find a range on the 'Citroen-ds-id.com' website HERE. Use the menu on the left hand side to navigate to 'Citroen DS', then 'technical data' and then to 'carburettors'. Unfortunately these are in French or German, but you will get the picture (quite literally).

When I pulled the engine from my car I was shocked out how dirty and oily my carb was. Initially I gave it a clean with white spirits. It was only a token clean of the outer surfaces and linkage mechanism. It just served to show how grubby the thing was. It all looked, well, a bit dull. 

After a clean with white spirits

After a couple of years(!) I got round to cleaning it in my blast cabinet with bicarbonate of soda. Bicarb gives a gentle clean and is water soluble - so there was no need to worry about jets getting blocked.

During soda blasting: Half and Half

Cleaned with Bicarbonate - May 2017

I was pleasantly surprised by how well it came up (it even had a bit of a shine). I planned to re-zinc all the levers, but I might have contented myself with leaving the body like that. However by this year I had decided to have the body vapour blasted.  That meant a complete strip down so that precision parts were not damaged or clogged with medium. 

With the engine nearly completed, finally this year I started the strip and rebuild. To start things off, I'd bought myself a basic service kit suitable for the DDE carburettor from Der Franzose as, unlike some other kits, theirs included both a new needle valve seat and the needle valve itself. It didn't however include a replacement gasket for the choke piston chamber cover, but that would be easy to make. I also got a new choke return spring from Citroen Classics.

I began taking lots of reference photos. Lots.......here are a few examples. Note the bicarbonate residue inside everything:

Spot the Bicarb

Note the tabbed washer fold the wrong way!

Carb Detail. You can never have enough reference photos

I needed to make a replacement gasket for the choke piston chamber cover

There are several common faults with old carbs that can prevent you from being able to set them up satisfactorily. As well as the dreaded warped base, I'd also heard stories of having to re-bush shafts and line the carb venturi to get the butterfly to fit/ seal correctly. Before I spent too much time and effort on this carb, I took it to the D rally in Little Horwood in June 2018 and got a second opinion on the wear in the primary shaft. Much to my relief (surprise?), it was deemed to not be too worn at all. There were no tell-tale signs of wear marks where the butterfly had rubbed the venturi. Perhaps this is one of the benefits of the car not being in use for 16 years.......

With a spring in my step I began to methodically take the carb apart. The hinge pin for the float was easily pushed out and the clip securing the need valve removed.

Removing the Float

Under the large brass nut by the fuel inlet is a wire filter. This was caked and would have to be cleaned.

Wire filter under the large brass nut

On a bvh car, the gizmo in the photo below controls the secondary 'accelerated idling' speed via the hydraulically operated 'accelerated idling device' that is bolted to it. The gizmo can be removed by carefully pulling out the brass collar that holds it in place. 

The Accelerated Idling controller is only found on carbs for bvh cars

On a manual gear change car, there is a strange looking 'gap' on the carb where this would otherwise fit and it's quite common for owners/ drivers to assume something is missing from their car(b)s.

I laid all the parts out in groups and in rough proximity to their locations on the body.

Laying out the carb parts

The auxiliary venturi are held in place with spring clips and can be lifted out.

Working around the body I removed all the brass jets and screws. 

There are two idling jets.

 Each idling jet is actually two pieces

In the picture below, the two main jets and the pump overflow valve have been removed from the bottom of the float chamber. The two brass screws on the left hand side are the air correction jets. Hidden beneath each of these is an emulsion tube. These can be carefully winkled out once the air correction jets are removed.

The main jets and pump overflow valve were unscrewed

Someone had taken my carb apart before. As well as the tabbed washer bent the wrong way, I discovered my carb had the wrong main jets: 1.20mm and 1.55mm instead of the correct 1.30mm and 1.75mm. I also discovered that one of the idling jets was wrong: 0.45mm instead of 0.50mm. I was planning on fitting 123 Electronic ignition and, to get the best out of this, needed my carburettor to be restored as close to 'factory-spec' as could be expected for a 50 year old carb. Ian K - another DS driver -  put me on to Southern carburettors where i was able to get the right jets. While I was at it, I got new screws for fixing the butterflies to the shafts and new tab washers.

With all the jets removed, I dismantled the butterfly and associated levers. In the photo below, the black knurled screw and lock nut on the right hand side is the 'throttle stop screw' and is used to set the angle of the primary butterfly for idling. Citroen Manual 518 (applicable to my DDE carburettor) tells the reader not to tamper with it.

Knurled throttle stop screw and locknut should not be tampered with.....

I had no confidence that someone had not already tinkered with it, and it all had to come off if the carburettor was going to be cleaned. I pulled it all off and would cross the resetting bridge when I came to it.....

There are lots of washers and spacers on the shafts that need to go on in a specific order - and this was where the carburettor parts diagrams came in handy. The top half was similarly dismantled and the parts laid out.

Just about everything accounted for....

With the carb dismantled I began the clean up and rebuild. I'd already decided to fit a threaded and barbed inlet tube to reduce the risk of an under-bonnet fire. You can read more about that in my post from October 2015. You can find  it HERE.

Threaded and barbed fuel inlet

If I'm honest, it took quite a lot of tugging and twisting for me to remove my old fuel inlet, so there didn't seem to be much chance of it working loose by itself. But make no mistake - these things do fall out and cars do catch fire. Now was the time to safeguard against that risk. Even if your inlet pipe seems to be securely fixed, this modification is worth doing for the barbed end alone.

Tapping the thread for a new fuel inlet

Although the carb base is warped, I didn't attempt to flatten this as I feared it would have removed too much material and left the base thin and weakened. The fibre spacer that the carb sits on is compressed and matches the curve of the warped base - so potentially should enable me to achieve a good air tight seal - even if I have to use a little sealant of some kind.

With the inlet hole tapped, the top and bottom body halves were given to my local engineer for vapour blasting.

Before vapour blasting.......

After vapour blasting......

I then gave the halves a deep clean in my ultrasonic cleaner to make sure any vapour blasting medium and swarf from the tapping was flushed out. I used compressed air to dry the parts and make sure that all passageways were clear.

The external brass screws were soaked in liquid 'Brasso' before being cleaned with a toothbrush. I then ran them through my ultrasonic cleaner - together with the jets and the fuel filter. I didn't fancy putting these small brass parts in the cleaner loose - especially the needle - so hung them on wires suspended over the cleaner tank. The auxiliary venturi were also ultrasonically cleaned. I didn't risk vapour blasting them as function was more important than look.

Brass parts after cleaning

The levers, rods and shaft ends were cleaned and then zinc plated..........

Zinc Plated levers and rods

With all the parts prep'd and ready, I began the rebuild. I laid all the parts out to mimic the exploded carb diagram. This way I could make sure that nothing got muddled, everything was assembled in the right order, and that all parts were accounted for as I went along.

Everything laid out as per the diagram for re-assembly

Reassembly of the bottom half went well. I used heavy grease to lubricate all the shafts and levers, but being careful not to get grease near the jets.

Assembly underway......

The butterflies are marked '85'. This denotes that the sides are not perpendicular to the flat faces - they are at an 85 degree angle. This is so that they can seal against the venturi. They fit on the shafts and in the venturi only one way.

Edges of the two butterflies are 85 degrees, not perpendicular to the faces

I hit a snag when it came to fitting the main spring on the primaty butterfly shaft: under tension, I couldn't get the end of the spring to to catch. Careful examination showed that the straight tang on the end was weakened and was bending. Eventually it fell off. All the Weber DS carbs from 1966 to 1975 use this same spring: part number 47610.068. Springs are tricky buggers: lots of permutations. Some turn clockwise, others widdershins. Diameters vary, coil numbers vary, tensile strength varies..... I could have just tried to bend a new tang from the remaining spring - but that would have altered it's length and so I wanted to avoid that. I searched high and low for a replacement but without success. The closest I found was Weber part 47610.063 (for a Ferrari 365 or Porsche 911). Unfortunately, although it looks the same, it has a different number for a reason - it's a different diameter - so no good...... 

Top spring: Porsche (small), bottom spring: DS (larger)

In the end Darrin, at Citroen Classics, came up trumps with a used spring. Problem solved.

The last stage of assembling the bottom half was to fit the lever that would connect to the top half. This is where the little rubber rings in the rebuild set come into play.

Rubber rings go on the rod ends before the spring clips are fitted

Moving on to the top half, I refitted the choke mechanism and the choke plate - again making sure that the mechanism and shafts were lubricated with grease. I refitted the new gaskets before fitting the new needle valve.

Needle valve seat in place

Unlike the original, the replacement needle valve doesn't use a black clip to hold the need valve in place.

Replacement and original needle valves

The float height is set by bending one or other tabs that form part of the float hinge. With the gaskets fitted, I made a card feeler gauge of the correct thickness (as taken from Operation DX.142-3 of manual 518) and measured then set the 'closed' height of the float.

Measuring the float 'closed' height

I then used another card gauge to measure then set the 'open' height......

Measuring the float 'open' height

.......before going back and checking the 'closed' height again. 

At the Little Horwood D rally, I mentioned to Toni Papa that I was rebuilding my carb but that I lacked one gasket for the piston chamber cover. Toni came to the rescue as he has a printer cutter and had been making himself some gaskets! I sent Toni a template and back came a couple of perfect gaskets. 

Toni's plunger apperture gaskets

With the piston chamber cover and new gasket fitted, the top and bottom halves were reunited. It only remained to hook up the lever linking the two halves - when another setback struck! The second and last small black spring clip that holds the rod onto it's lever end, snapped! Just like the springs, these proved very elusive to get hold of as Weber do not manufacture this part anymore. I got lucky when one of my leads rummaged around on a shelf and found me three.

One of the rod clips broke in two and had to be replaced

Here's the finished carb......

.......and below are a couple of 'before' and 'after' photos.

Detail: before

Detail: after

With the carb rebuilt, I put it in situ on my inlet manifold - just to test that the mechanism moved freely and as intended, and without freeplay. I did NOT fold the tabbed washers at this stage as, because of heat expansion, I want to repeat these checks with the carb fitted and the engine warmed up. I labelled the carb up to remind me when the time comes.

I will cover Carburettor set up in a future post. To be honest, I'm still researching it!