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).
Carburetter adjustments and design modifications for improving slow running performance.
| Identifier | ExFiles\Box 13\3\ 03-page342 | |
| Date | 7th September 1931 | |
| Hs{Lord Ernest Hives - Chair}/Swn.1/AM 7.9.31 contd. -2- Slow Running. The double slow running feed gives good results over the idling range when correctly adjusted i.e. .025 jet, the front adjustment unscrewed 1 1/4 turns and the restriction (fixed) removed from the back adjustment. Starting from cold is rather difficult as even when the adjustable choke is passing no air there is an air bleed from the atmospheric side of the throttle (front adjustment) into the back adjustment which is on the suction side of the throttle. This condition occurs with the throttle almost closed, for dead slow running or starting. In the previous twin carburetters we adopted the single feed adjustment eccentric about the throttle edge, this giving just as good result over the idling range with greater ease of starting. This scheme is to V.1058 and simplifies considerably the casting with regard to passages. The eccentricity of this type of feed should be sufficient to expose complete feed hole on the suction side of the throttle also to completely cover it, the throttle being in a closed position. We find that .075" dia. feed hole in the rotational plug appears to give good results in conjunction with .032 jets and centre brass venturi to be .171" dia. It is unnecessary to make this centre venturi as a separate piece from the adjustable choke controlled by the quick thread. Considerable improvement to the evenness of the slow running was obtained by grinding out the throttle spindle bushes flush with the carburetter bore and the throttles fitted having no flats filed on them. | ||