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).
Carburettor performance issues, including a diagram illustrating fuel delivery at small throttle openings.
| Identifier | ExFiles\Box 121\2\ scan0080 | |
| Date | 23th January 1929 guessed | |
| contd :- -3- The disadvantages enumerated above have been quite sufficient to prohibit the use of this type of instrument on our cars. Certainly there have been numerous adjuncts developed to attempt to overcome these difficulties - chiefly seen on American cars such as priming pumps for acceleration - but none of these seem entirely satisfactory and seldom retain their tune over long periods necessitating frequent re-adjustment. Let us examine what happens during snap acceleration with the static carburetters :- When running along on top gear with very small throttle opening - say about 4 m.p.h. in traffic - the whole mixture is being delivered by the slow speed jet, there not being sufficient velocity through the choke to draw petrol from the diffuser - see sketch. FIG. 1. Now if the throttle is opened gradually the engine speed increases and the air velocity in the choke rises sufficiently to draw fuel from the diffuser. The mixture is governed up to this point by the position of the throttle as it traverses the discharge slot. At throttle openings above this the diffuser fulfils the demands of the engine. contd :- [Text from diagram] MIXTURE AT SMALL THROTTLE OPENING DRAWN FROM IDLING SYSTEM. AIR VEL. TOO LOW IN CHOKE TO DRAW FUEL FROM DIFFUSER | ||