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).
The operation and features of a suction-controlled carburetor, including its piston, gaskets, accelerating device, and dash control.
| Identifier | ExFiles\Box 122\4\ scan0015 | |
| Date | 9th November 1934 guessed | |
| -2- The advantage claimed for suction-controlled metering over metering under direct throttle control is that it makes it possible to employ a leaner "economy" mixture, while at the same time it enables better part-throttle performance and gives freedom from low-speed tip in lean spots. A suction controlled device as described in the foregoing requires a number of safety features to make it stable in operation. In this carburetor the actuating piston is made of yellow brass and works in a smooth, inserted brass cylinder. The lower end of the cylinder is vented into the lower part of the throttle barrel with a screen H in the vent to prevent dirt particles from entering and sticking the piston. As there is air leakage past the piston, particularly when the latter is held up by high suction, this air must be clean. The screen is so made that no dirt particles can pass through it and into the cylinder. To prevent fuel which is splashed around in the bowl from working into the suction-controlled cylinder and thence into the throttle barrel, two gaskets are employed, I and J, above and below the nut K respectively. When the piston is up, the lower gasket seals the cylinder from the bowl, while when it is down, the upper gasket forms the seal. The accelerating device is of the dwell type; that is, when the throttle is opened an accelerating charge is forced out of the tube L, and when the throttle opening motion stops, the accelerating device continues to discharge for a definite length of time. The advantage of this type is particularly noticeable at low speeds, when more than just a rapid accelerating charge is sometimes needed. The dash control lever is mounted on a cross-shaft instead of on the choke shaft, as in most plain tube carburetters. This method is used for better control during the warming-up period. The dash control can be pulled out a considerable distance before the choke disk itself is moved to close, and during this initial motion of the dash control the throttle is opened slightly by lever C and the mixture is enriched by the warming-up lever P lifting the warming-up needle Q and supplying extra fuel from the bowl to the main jet. When the dash control is moved beyond the warming-up range, the pin R engages with the connecting link S which closes the choke disk. | ||