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).
Technical analysis of carburettor performance, modifications, and issues such as flat spots on various engine types.
| Identifier | ExFiles\Box 123\1\ scan0081 | |
| Date | 27th January 1941 | |
| Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}3/ET.27.1.41. - 3 - The point is that all these effects are cumulative and tend to upset test bed prediction. This type of carburettor is obsolete on 6 and 8 cylinder engines, and items 1. and 3. do not hold for dual aerotype units. But item 2. is still there and this is probably the most serious. On 4 cylinder engines a single carburettor may be used and this brings back items 1., 2. and 3. in force. Low speed direct gear pick up with gentle throttle opening is a critical condition on our Stromberg units, and performance at this point determines more than anything else our metering jet size and the presence or absence of good part throttle economy. Thus, to date, we have shewn that pick up distribution may not be all it should be, and that pick up is the most important condition. We are not going to ask that all carburettors be mounted so as to give forward throttle bias with the object of better distribution. We do suggest, however, that the bias is not as important as has been supposed and that the resulting float chamber position gives a real advantage. It means that the float will not be mounted at right angles to the engine. This type of mounting makes fuel level very uncertain due to engine rock, and should be avoided at all costs. Because of this engine rock and in order to make Wraith idle, the level had to be dropped 1/8" below that for which the carburettor was designed. This resulted in a flat spot which it is fundamentally impossible to remove. Every production Wraith has that flat spot, however slight, and it is nearly always possible to clock the engine right out on a slight rise once it has been located. 22-G-IV was very carefully tested by Ratcliffe for change in performance after swinging the carburettor through 90° in order to overcome flooding troubles. The throttle now gave bias towards the front and full throttle acceleration figures throughout the range actually improved by about 5%. It was not possible to clock the engine out on a left hand bend with the fuel flowing away from the discharge tube. | ||