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).
Visit to S.U. Carburetter Co. regarding a horizontal carburetter for the 20/25 model.
Identifier | ExFiles\Box 31\5\ Scan154 | |
Date | 11th April 1934 | |
COPY. HORIZONTAL CARBURETTER FOR 20/25. Visit to the S.U. Co., Birmingham. A visit was made to the S.U. Carburetter Co. of Birmingham for the purpose of discussing the various points, with reference to the adaption of a fully expanding carburetter of our own make (LEC.368B) to the 20/25 HP. unit, the principle of the carburetter being similar to their own design. The first point of interest is the fact that most of the development work carried out by us so far is on similar lines to that which the S.U. Co. have taken in experiments carried out by them from time to time in an endeavour to improve their own carburetter. The conclusions arrived at are in both cases very similar. The different points in comparison may be summarised as follows :- Firstly, the S.U. Co. have fitted (experimentally) a throttle edge (for improved slow running), incorporating a stop, to prevent the piston from coming right down to the bottom of its stroke. This, as has been explained before, gives an initial piston lift, to make way for the effect of a low speed choke. They ran into the same trouble from pick up and snap acceleration as we are experiencing at the present time. Their explanation of this characteristic is as follows. On a gradually increasing throttle opening, the low speed choke (throttle edge), slowly fades out, and the gradually increasing air velocity causes the main jet to come in, and bring about the necessary changeover from the low, to the high speed jet. This means, that up to a certain air velocity, the engine is running off the throttle edge, and the main jet will not come in until this velocity has increased sufficiently, due to the effect from the initial lift of the piston. It can be understood that when the throttle is suddenly snapped open wide, from an idling speed, the throttle edge supply immediately cuts out, and there will be a delayed action, while the main jet comes in. | ||