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 road tests of a Phantom II twin choke carburetter fitted to car 22-EX.
| Identifier | Morton\M19\ img143 | |
| Date | 2nd April 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey} c. to Sg.{Arthur F. Sidgreaves - MD} Gsr. c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to Hy.{Tom Haldenby - Plant Engineer} ORIGINAL PHANTOM II TWIN CHOKE CA BURCTTER TESTS ON CAR. We have now had some road tests with the twin choke carburetter with promising results on 22-EX. We were very surprised to find that there was considerably less trouble with carburetter noise than we had anticipated from our test bed results. What noise does exist should not be difficult to deal with. For these tests no special intake silencer was fitted - the carburetter just having its original slotted cover over the intake. Starting up from cold is readily accomplished with the mixture control put over full rich which lowers the small low speed chokes and so cuts off the slow running emulsion air. This gives high suction and rich mixture for a cold start. There appears no need for a separate starter carburetter. A noticeable feature is that the car can be driven away immediately from a cold start and accelerated without any popping or spluttering with the mixture control in the rich position, but not so rich as to cut off the slow running emulsion air - i.e. about 2 notches from the extreme rich position. This appears to be an improvement over our std. carburetter and is no doubt attributable to the throttle edge slow running operation (on the twin choke carburetter) giving higher velocity and suction than the relatively large slow speed choke of the std. carb. The "change over" position when the throttle is opened quickly is bridged over by the accelerator pump and the 'well' in the diffuser and is therefore less dependent on heat for opening up. Cold distribution seems good and the hot spot soon gets hot. In a very short time it is possible to restore the mixture control to the normal running position after a cold start. Slow running is good and positive but at first we encountered a little trouble with dirt getting into the jets because we operated without a filter in the slow running system. We did not use a filter because with the very low gravity head from the std. Autovac. we did not wish to restrict the flow at max. output. Snap opening up was good and we could not stall the engine by kicking the accelerator pedal full open from low speeds. So far we have not done much work on the accelerator pump as it appears to work quite well. We may find its action can be reduced but have had no trouble with over-richening, even when working the accelerator rapidly up and down. | ||