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 description of the Zenith carburetter's slow running, starting, and accelerator pump schemes.
| Identifier | Morton\M19\ img167 | |
| Date | 5th May 1931 | |
| -3- Zenith slow running Scheme. We have just examined one of the latest double choke Zenith carburetters (36 D.U.P.) which has one or two interesting features. The slow running lay out is shewn on appended sketch. The mixture discharge holes are at one edge of the throttle only. One small hole is about 1/8" above the throttle edge when closed and therefore always fully exposed to the induction pipe depression. A lower hole - which can be adjusted for size by removable jets - is just shut off from suction when the throttle is fully closed and in just position of the throttle exposes about half of the hole below the throttle edge. Four large holes feeding air only are uncovered with slight opening of the throttle. These four holes have no connection with the idle mixture passages but are drilled through to the atmospheric side of the choke. The apparent purpose of these latter four holes is to prevent a rich spot just after the throttle uncovers the lower of the two mixture holes by allowing the admission of more air than can normally flow past the edge of the throttle at small openings. The amount of air dilution into the mixture passage is regulated by means of a taper screw. There is only one adjusting screw and this serves for the system of each choke. The easy starting scheme consists of an additional jet to the slow running and is provided to considerably increase the mixture available for starting. This jet is fed directly from the float chamber and communicates via a passage and starting cock to the top of the normal slow running jet. This system has the advantage that one does not get an excessively wet mixture on starting up, the same as results if the air supply is cut off, because the normal air supply, providing good atomisation, is still available past the seating of the conical adjustable air screw. Accelerator Pump. A very simple pump is employed on the Zenith. It is totally enclosed in the float chamber; the operating shaft passing through the upper half of the float chamber. | ||