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 slow running scheme and modifications for twin choke carburettors.
| Identifier | ExFiles\Box 13\3\ 03-page315 | |
| Date | 5th May 1931 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Lov.{Mr Lovesey} c. Sg.{Arthur F. Sidgreaves - MD} c. Wor.{Arthur Wormald - General Works Manager} E.{Mr Elliott - Chief Engineer} c. Da.{Bernard Day - Chassis Design} Ry. r7080. Hs{Lord Ernest Hives - Chair}/Lovl/AHS.5.5.31. X1053. P.2. TWIN CHOKE CARBURETTARS. The slow running scheme we have employed on the twin choke carburetter fitted to 27-EX (at present at West WitteringHenry Royce's home town), is the same in principle as we use on our aero carburetters. We have effected this in a temporary manner by deleting the rear mixture hole adjusting screws and plugging up and replacing the front adjusting screws by brass cocks having the mixture hole, which comes out at the throttle edge, drilled eccentrically. See appended diagram. Mistaking the modified scheme for the original one on the car now at W.W. is quite easy as in external appearance they are very similar as we used up some of the original bits in making the modification. We understand it is proposed to return again to the original scheme with the two discharge holes and adjusting screws on each side of the throttle and the 'club foot' on the one throttle edge. We tested out this scheme on the first model but had difficulty in getting good carburation over the idling range. The troubles may be explained by reference to appended diagram. The variables we were able to test during these experiments were :- Various combinations of the fore and aft adjusting screws controlling the size of mixture discharge orifices at the throttle edge. Various idle metering jets and various adjustments of the choke round the idle jets. The best arrangement was found to be a jet of .015" dia and adjustment of the choke to give an approximately correct mixture with the throttles opened to just below the position where the main diffusers started. | ||