The engine has a semi-expanding type carburetor which uses a large air cleaner. Building an engine of that type is described in my Semi-Expanding Carburetor Build Note. Click here to download a PDF copy (20Mb).
I did have a completed spare engine fitted with a semi-expanding carburetor so, in the end, I decided to use it rather than follow my original plan of building a new engine. Below are detailed pictures. Unlike Pocher kits, there is no accelerator pedal mounted off the gearbox. Rolls-Royce actually mounted the accelerator pedal on the chassis rail. Click here for a comprehensive story of the build.