From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Report page discussing carburetter performance, features, and specific design elements like the main jet and throat.
| Identifier | ExFiles\Box 122\1\ scan0031 | |
| Date | 3rd December 1928 | |
| OY3.R.12.3.28 - 2 - December 3rd, 1928. (6) The jets seem to be free from blockage with any reasonable filtering of the fuel. (7) Freedom from popping in exhaust. (8) Car in normal action sooner after a cold start. (9) Freedom from chauffeur-interference. The carburetter once set is practically not adjustable except within very narrow limits. (10) The consistency between individual carburetters appears remarkable, so much so that it would appear desirable to cut out all adjustment except possibly idling speed and idling air, The makers tell us that this is actually done on carburetters for commerical vehicles. This looks like a formidable list and we may be wrong about several of these points, but still the carburetter is undoubtedly good enough for a thorough trial. The carburetter has a single intake and all air supply is internal so that an Air Cleaner can be installed effectively. Vertical Carburetter. In common with all their automobile production it is a vertical carburetter, the horizontal ones having been found impossible for the addition of their various devices and abandoned last year. (1) Main Jet. This is diffuser type having a small well for moderate speed changes, and an "air-bleeder" for regulating the partial throttle mixture ratio to give the desired "loop" to the richness curve for economy at ordinary road speeds. The jet itself is interchangeable for varying restrictions. The air bleeder is also changeable. This jet discharges into a small internal throat which is used to keep semi atomised fuel off the walls of the main throat and to concentrate the higher velocity air at the center of the passage around the jet. (2) Main Throat. This is changeable for engine conditions the aim being to use the smallest possible throat which will not unduly choke the engine at the maximum speed at which it normally operates (say 60 m.p.h.) We have so far arrived at a 1-5/16" throat but this may prove too small for best performance at speed. However we have had 80 m.p.h. on the car mentioned above. -continued- | ||