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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).
Test report on the Phantom II semi-expanding carburetter, detailing weaknesses and potential improvements.

Identifier  ExFiles\Box 13\3\  03-page430
Date  20th June 1932
  
87080.

E.{Mr Elliott - Chief Engineer} From Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}
c. to Hcr.
c. to Ey.

Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}2/MA.20.6.32.

PHANTOM II SEMI EXPANDING CARBURETTER.

Since our last report we have had the opportunity of testing the carburetter Lec.3026 which has been designed to incorporate all the improvements carried out on the original carburetter Lec.2972.

Lec.3026 is scarcely up to the performance and behaviour of the improved Lec.2972, both in acceleration and metering under all conditions. The main difference is shown in the Sketch (V.1389).

The carburetter Lec.3026 possesses a momentary weakness when throttled back from low speeds full power, due to the delayed time to fill up the diffuser to a normal level. The reason for this is the excessive capacity below the diffuser and the petrol passage to the slow running unit.

This weakness can be partially overcome by fitting an extension 1.00 long to the slow running jet so that the low speed jet is quicker in running after the throttle has been partly closed.

There is however still a tendency to weakness on the part of the diffuser under the above conditions:-

During our tests we had an external feed pipe .125 bore from the diffuser to the slow running, there being no signs of weakness on closing the throttle. If this pipe be substituted by one of .250 bore the engine cuts out through weakness when throttled back, this emphasising the importance of keeping the capacity as little as possible, yet without restriction to the flow.

Lec.3123 shows a layout which would conform with all our results obtained on the test beds, that is,
  
  


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