Replacing the primary jet in a 2CV carburettor

The later models of 2CVs come with a twin choke carburettor with the primary (smaller) being used at low revs and a mechanical linkage opening the secondary (larger) as the throttle is depressed further.  Fuel is allowed into the venturi from the bowls by small brass jets (screws with calibrated holes in the middle), the size of which controls the fuel/air mixture.  As standard the primary jet is a 102.5 which, for modern fuels, is slightly undersized leading to a slight flat spot in acceleration from low revs.  To eliminate this fitting a 107 jet is recommended.

The secondary jet is easily accessible at the base of the fuel bowl but the primary is a bit more complex.   The first step is to take the top off the carburettor, with the elephant’s knee (air intake pike) removed there are six flat head screws – one of which holds the choke cable in place – and the top of the carburettor lifts off.  As the jets are at the bottom of the bowls they will need any residual petrol in them removing.

Interior of a 2CV carburettor

Now comes the tricky part.  On the back right (as you look at it when standing in front of the car) corner of the carburettor is a 12mm bolt head – this is the access port to get to the primary jet.  With that bolt removed there is now a head on approach to the primary jet – shown arrowed here:

Interior of a 2CV carburettor showing primary jet location and access

The jet has a slot cut in it for a flat head screwdriver which needs introducing through the access port.  Fortunately in my tool box I happened to have a long electricians’ screwdriver that could have been specially made for this exact job as it extended clear of all the obstructions in this area and made this job much easier than I was anticipating.

Using a long screwdriver to unscrew the primary jet from a 2CV carburettor

With the jet unscrewed it will need removing from the carburettor.  As it’s brass the traditional use of a magnetic pick-up isn’t an option so I found a cocktail stick worked well as it wedges in the middle of the jet without damaging it and holds it just enough to withdraw it.

Using a cocktail stick to remove the primary jet from a 2CV carburettor

Fitting the new jet is, of course, the reverse of removal – making sure to reconnect the choke cable when replacing the top of the carburettor.

When everything is buttoned back up check the car starts and runs – it will probably need some cranking to re-fill the carburettor bowls.  Then, when the engine is nicely up to temperature the idle will need re-setting.

Liked on YouTube: Burton 2CV Parts – Testing Carburettor

We offer a wide range of new and reconditioned carburettors. Both for very early Citroën 2CVs, and for the later 2CV6s. The double barrel carburettors are now available, completely new.

In this short film we like to show you how we test each and every one of them. In our experience all these carbs need a little adjustment to make them work just perfect.

Solex 23/36 CISC carburettor

The Solex 23/36 CISC carburettor was fitted to the 2CV, Dyane, Visa and LN(A).  Leaving aside the 652cc engines, there were two models fitted to the 602cc engines and they differ in the sizes of the chokes.

Information on these in the Citroën workshop manuals is contained in a few cross referenced tables which are just about intelligible if you are looking for information on a specific car but make it very hard to come up with a simple guide.  Not that I’m going to let that stop me – here’s my working overview of the main types of 23/36 carbs.

Car Reference First choke venturi [mm] (area [mm^2]) Second choke venturi [mm] (area [mm^2]) First choke main jet Second choke main jet Idle jet First choke air correction jet Second choke air correction jet Pump injector Needle valve seat
2CV/Dyane (1978-07)   197   21 (1385)   24 (1810) 120    70    40 1 F 2 2 AA   40 1.7 (Ball type)
2CV/Dyane (1980-07)/LN 225   18 (1018)   26 (2124) 102.5   87.5   39 1 F 2 2 AA   45 1.7 (Ball type)
Visa/LNA              209   21 (1385)   26 (2124) 125  130    41 120  160   40 170 (Ball type)


Car: This is the car that used this carb, this is a rough guide – for more detailed information you’ll need to dig into the workshop manuals.
Reference: The Solex reference that is supposedly on the carb, not found it on mine yet.  However, the venturi sizes are moulded onto the bowl either side of the Solex logo and that’s how you can tell which model you have.

The 197 (21-24) carb is sometimes referred to as a “Dyane carb”, probably because it seems to have first appeared on the M28 engine used in the Dyane. However, both 2CVs and Dyanes had this carb and then the latter – and more common – 225 (18-26) carb.

Carburettor fettling

After the previous fun and games with the engine I had some outstanding business with the carburettor. Firstly the elephant’s knee* had split (gaffer to the rescue for the trip home).

The top of the carb comes off with six screws – one of which holds the choke cable in place.

With the top of the carb off the fuel was siphoned out of the bowls – there was a bit of clart in the bottom of the bowls which I removed but nothing to worry about.  The jets are easy to access with the top off and – not that I found any obvious obstructions – they were cleaned with spray solvent and some plastic brush bristles.

To replace the top gasket the floats need removing, the pin that forms the hinge is a friction fit and needs drifting out – I used a cross head jeweller’s screwdriver.  With the gasket back the float heights were equal at 18mm so no problems there.  Also in the top of the carb is the needle valve activated by the floats and, whilst that wasn’t obstructed, it was pre-emptively cleaned as well.

With the top back on the only remaining item was the new elephant’s knee which, being unperished,  went back on much more easily than the old one.

2CV carburettor and airbox hose

* The pipe connecting the airbox to the carb, this is what I always called it when I was a nipper – no idea if anyone else calls it that.