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 from The S.U. Carburetter Co. Ltd. about variations in the thermostatic carburetter.
| Identifier | ExFiles\Box 121\4\ scan0213 | |
| Date | 6th October 1938 | |
| TELEPHONE: BIRMINGHAM EAST 1171. TELEGRAMS: FLEXCARBUR, BIRMINGHAM. 1484. THE S.U. CARBURETTER CO. LTD. PROPRIETORS> MORRIS MOTORS LTD. ADDERLEY PARK, BIRMINGHAM, 8. VISCOUNT NUFFIELD CHAIRMAN OLIVER BODEN, O.B.E. VICE-CHAIRMAN T. C. SKINNER, M.I.A.E. MANAGING DIRECTOR YOUR REF: OUR REF: RLK/ER 6th October 1938. Messrs. Rolls-Royce Ltd., D E R B Y. File Dear Sirs, For the attention of Mr. Salt. We believe you want some information as to the variations which can be effected in the thermostatic carburetter. So far as the owner is concerned, the only adjustment provided is the adjusting screw which limits the travel of the needle. In point of view in getting out original settings, however, there are the following variables:- taper on the needle, diameter of disc on the needle, position of disc on the needle, and strength of spring. So far we have restricted the variation in needles to .004" taper per 1/8", .008" per 1/4" and .016" per 1/2". The maximum possible travel on the needle is 3/8". The position of the disc may be varied in order to control the length of this travel down to a minium of 3/16". If further variation is required, the next needle should be used. The diameter of the disc controls the amount of air admitted to the auxiliary carburetter, and thus the fast idling speed. When this is varied, however, the spring must also be varied - usually to a rather greater extent than would at first be anticipated since when a larger amount of air is admitted the pressure drop along the piping is also greater and thus the spring has to be reduced to allow for this pressure drop, as well as for the reduction in area of the disc. Needles are stamped with the numbers '4', '8' or '16' as the case may be, and the discs are stamped with -1- | ||