It should actually, be called an 'atomizer', indeed, it should mix very fine droplets of fuel and not gas, with the air. The carburetor should produce, purely through the suction effect of the fast flowing air-stream, a favourable fuel-air mixture for almost any operational condition. For decades, it had been the only fuel-air mixing system for the petrol engine. After 1952 the fuel injection also came into play. Ever since a Lambda regulated mixture was required, only the Ecotronic-carburetor could keep up, indeed, only for a short time. After that - at least as far as motor cars are concerned - the era of the carburetor-technology was over.
Should no petrol injection system be installed, one or more carburetors must be placed between the air intake filters and the engine. There are carburetors which work under a constant vacuum (CV-carbs), most of them however, work with variable vacuum. This is generated by a choking passage in the tube. The narrowest point is an important index for the size of the carb. A conduit leads off from the narrowest point, which is connected to the hopefully, always well filled store room (float chamber). From here the air flow sucks in the fuel. To be able to regulate this more precisely, it is fitted with an exactly measured main jet (nozzle). The accelerator pedal is connected to the throttle valve, which is installed directly in the choking passage of the air flow on it's way to the engine.While the oldest vehicles were fitted with an up-draught carb, where the air flow was bottom-to-top, the side-draught carb, with it's horizontal- and the down-draught carb (see picture), with it's vertical choke funnel, asserted themselves. The air from the air filter comes in at the top, and at the narrowing, is substantially accelerated. This is where the mixing tube comes in (center) and the main jet (below it) dips into the fuel. The fuel level in this chamber is held relatively constant by the float regulation. When the float has reached a certain level, the influx of fuel is stopped by a needle-valve. On the right, the left and below the mixing tube and the main jet, the parts of the idle-regulation can be seen. This had already, in the 1970s, become fairly complex because of the beginnings of emission control. 11/11