Dinsen > Matra Murena > Solex 34CIC > How it works

How it works

The 34CIC is a Solex double barrel down draft carburettor with manual choke, accelerator pump and anti-dieseling valve. This page contains som background information about it.

I owe much of the information contained herein to Roy Gillard.

How it works

The image below is a principle-diagram showing the components of the carburettor (picture is taken from Espace Murena):

Solex 34CIC cut

The following description describes the principal operation of the Solex 34CIC and pictures of one. Different versions of this carburettor exists so details may be different from yours. Carburettors are fascinating innovations. Carefully inspect your carburettor before attempting to work on it.

Fuel enters through the inlet pipe in the very upper left corner and flows through the channel to the needle valve P. The float chamber is filled up through this valve, which is controlled by the float F ensuring a constant fuel level. Excess fuel is returned through the fuel return pipe which is next to the inlet - this takes any fuel not going into the float chamber back to the fuel tank.

From the float chamber, the fuel flows through Gg and up through the two emulsion tubes. These control the mixture of air and fuel and specifically the amount of fuel at a specific airflow through the carburettor. The very rich mixture of air and fuel is blown through the main jet K into the venturis.

Accelerator pump is shown to the far left (membrane, spring, and lever) and it pumps fuel into a channel up into the top of the carburettor and through the accelerator jet i.

Fuel for idling is sucked out of the float chamber through Gg up to the valve Et that opens the fuel channel down to the idle jet where a rich mixture of fuel and air is produced. The function of the electromagnetic valve is to cut idle fuel supply when ignition is turned off - this prevents run-on of the engine after ignition is cut. The idle mixture adjustment screw is in the bottom left side of the right part of the drawing.

The linkage on the sides of the carburettor controls the throttles and accelerator pump in the following way: The cable directly controls the primary venturi ("1er corps") through the link, whereas the secondary throttle (in "2e corps") is only engaged when the pedal passes a point about 2/3s from full. The accelerator pump is adjusted to be engaged in the same way by the throttle pedal - it deposits an additional small amount of fuel directly from the float chamber into the primary venturi which ensures good enrichment when the pedal is floored.

Idle speed of the engine is adjusted on the screw on the right side of the carburettor. This adjustment directly limits the closing of the primary throttle valve.

Around the 34CIC

These are pictures taken when I replaced gaskets in my carb.

Solex 34CIC seen from the left side showing the accelerator pump linkage (lower middle) and fuel entry and return pipes (upper right)
The Solex 34CIC seen from the left side showing the accelerator pump linkage (lower middle) and fuel entry and return pipes (upper right). The idle jet (CO adjustment) is accessible through the hole in the base of the carburettor in the lowest right corner.

The Solex 34CIC from the rear (front of the car) showing the anti dieseling valve in the upper right. The bolted on cover in the right is the OVAD valve (Ouverture du volet après départ à froid) which kicks the choke open when the engine requires more air.

Still the same Solex 34CIC, this time from the right side showing the throttle and choke likages. The link sitting downwards on the picture is normally going horisontally to the pivot which is controlled by the throttle cable. The choke cable comes in from the upper left. Tje OVAD valve is clearly visible here.

Visible here is the accelerator pump, trottle and choke linkage and fuel entry pipe. The idle speed screw is in the lower right corner.

A look from below up into the venturis

A view into the carburettor with the top part removed (the gasket sits between these two parts) into the float chamber which actually consists of two connected chambers.

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Page updated: 2019-12-01 07:15:06