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).
Notes on carburetter settings, discussing performance, economy, and cold weather issues.
| Identifier | ExFiles\Box 147\5\ scan0185 | |
| Date | 4th September 1941 | |
| -cont'd- - 2 - Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}10/SW.4.9.41. Notes on the Carburetter Setting. The carburetter has been set as economically as possible without loss of top speed or performance. It should therefore be possible to maintain this setting throughout the year. A 30 m/m.{Mr Moon / Mr Moore} throttle body has been substituted for one of 36 m/m.{Mr Moon / Mr Moore} dia. without loss of top speed, and this should help a little with the flatness which we anticipate in cold weather. The chief object of the small throttle body is, of course, to cut out the idle system as early as possible, and so get on to the main jet or economy part of the metering curve. It is certain however, that trouble will still be experienced when the underbonnet temperature falls. With the small engine and large underbonnet space it would not be surprising if, when the air temperature falls below 0°C, the jets have to be increased sufficient to cause a 10 MPG drop in consumption. While on the subject of economy loss in cold weather, it may be mentioned that the carburetter setting necessary for B.80 (4-B-50) in cold weather has recently been tried on the Test Bed. Compared with the ideal it is very strong full throttle. At 3,500 RPM, the flow is 120 pints/hour compared with the ideal demand of 89 pints/hour. Furthermore it is difficult to believe that B.V. with its economy setting (LB1 needles and drilled-out jets) will not be in serious trouble this winter. Two points should be borne in mind. (1) B.V. as at present in customers' hands is weak in really cold weather if no blanking plate is fitted. This is true despite expanding carburetters and a rich setting. (2) B.11. carburetters were set right to the limit for economy. Radiator shutters pulled them through in cold weather. It is true that the carburetters were unchanged on M series with fixed shutters. The answer to this is that there were complaints of weakness on M series at Chateauroux, and that in any case M series carburation would not stand investigation in cold weather were a Startex fitted. With hand controls it is easy to cover up the weakness and forget about it. -continued- | ||