SU Carburettor On Automotive Engineering

In a wonderfully simple SU carburettor., the varying exposure of a tapered "metering needle" is the mechanical equivalent of the electronic engine management system's lookup table or "engine map". Naturally, in the modern electronic engine management system, there is a lot more optimization going on, but the SU had the really important issue - correct metering and dispensing of fuel for the volume of air drawn through - very well under control.

SU Carburetor

SU HS6 Carburettor

The SU carburettor is of ac onstant Velocity, variable choke design that is, by varying the position of the dashpot (12) as a function of the volume of air the engine draws, the cross-sectional area of the throat of the carb is varied, which keeps the velocity at the venturi point constant and by keeping the velocity constant, it is fairly simple to meter the fuel for a given volume of air induced, although this leads to somewhat of an oversimplification in fuel metering, since the fuel should be metered as a function of mass of the air being ingested and not just volume (as density of the air, which can vary due to things like weather, season and altitude, is not compensated for). That is why I like to adjust the mixture for summer and winter. Itu sebabnya saya ingin menyesuaikan campuran untuk musim panas dan musim dingin. Other than that, they seem to thrive on neglect, I honestly don't understand why some owners seem to continuously need to fiddle with them.

Carburettors have been around since the beginning of the automobile. Over the decades, carburetors have varied from the simple to the very elaborate. All carburetors share one common property: they mix gasoline with air in the proper ratio for combustion over a wide range of conditions, including engine load, altitude, engine temperature, and air temperature. Generating a useable air-fuel mixture has been accomplished in a wide variety of ways. In the early days, the RPM range of internal combustion engines was limited so a wide range of an air/fuel mixture was not as important and therefore carburetors for such engines were often very simple devices. Early carbs relied on moving air to draw fuel out of an orifice where it then traveled through the manifold to the combustion chamber. The fuel openings (called “jets”) were fixed so a certain amount of air flow was necessary to draw the fuel out. The larger the fuel openings, the more air flow necessary to start the fuel delivery.

As engines became larger and the RPM ranges increased, larger amounts of air/fuel was necessary. At idle, the air speed was too slow to draw fuel from the jet so idle circuits were added these were usually small openings near the throttle plate. These idle “jets” would supply fuel until larger throttle openings allowed sufficient airflow to cause the main jets to come into play. As the need for more air/fuel increased, it was found that the main jets could not be sized to supply sufficient fuel at high revs without compromising the effectiveness of the carburetor at low revs, so power valves were added to provide additional fuel under conditions of high load and/or power demand.