Benz Reichspost Bus 1913In this restructuring was a very tricky case to solve. The original engine (built 1913) has been damaged and it was because of the First World War, that there was a lack of spare parts or they were used for other purposes. An old airplane engine was then discovered and installed. The problem was, however, that this was a four-cylinder engine with over 6 liters capacity. He needed an abnormal amount of iddling mixture (which really was not necessary anyway because he is always running in full throttle range).
The idle mixture system of a normal fixed venturi carburetor could not deliver this through the small holes. They had tried different carburetors, but it always came to the same bad result. The only option was to install a constant depression carburetor which works self-controlled. This has been realized by two two inch HD8 carburetors (like a Jaguar).
In order to achieve the best possible mixing ratios, various needles were tried. Now the bus runs perfectly.
Thanks to Nikolaus Steinmetz for the images