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).
Letter to S.U. Carburetter Co. Ltd. regarding troubleshooting a 'flat-spot' with H.4 carburetters on a 4 1/2-litre Bentley.
| Identifier | ExFiles\Box 121\4\ scan0225 | |
| Date | 27th October 1938 | |
| 1484 Experimental Dept. Rm{William Robotham - Chief Engineer}/CTS.{C. Trot Salt - Carburation}9/MH.{M. Huckerby} 27th. October 1938. The S.U.Carburetter Co. Ltd., Adderley Park, BIRMINGHAM, 8. For the attention of Mr.Cooper. Dear Sirs, With reference to the H.4 carburetters which we are at present testing on the 4 1/2-litre Bentley. We have an elusive "flat-spot" which is in evidence at full throttle, and lasts over a range from 500 R.P.M. to 1500 R.P.M. As you know, we have been using needles to try and get over this trouble, which are richer on the third and fourth dimension, and you will agree that one would expect these richer needles to be a cure; we refer to the "RRX". But they do entirely cure the trouble. We have found, however, that by fitting .100 jets and L.B.1 needles everything is O.K., and actually petrol consumption is slightly improved. The peculiar thing is, that this change, although giving a richer mixture half way down the needle, does not give richer mixture at the lower speeds, full throttle. There is probably a catch in all this somewhere, and incidentally we have cancelled out the damped pistons. But we would like the dampers promised by Mr. Morris as soon as possible. In the meantime, will you please let us have as soon as you can, two sets of .100 jets to suit the automatic | ||