Technical memorandum regarding the performance and adjustment of an expanding carburetter.
| Identifier | ExFiles\Box 11\4\ 04-page047 | |
| Date | 7th May 1932 | |
| Re: EXPANDING CARBURETTER. When gradually accelerated in top gear the suction piston should commence to lift at approximately 35 M.P.H. If the car is run under full throttle conditions top gear the piston should lift at 25 M.P.H. These conditions are almost identical with the observations you report. The piston is set to rise slowly as this gives the best acceleration results. If it is made to rise much quicker popping back would occur when vigorously accelerated. One point we should like to know is the maximum amount the piston lifts at high speeds. This should be approx .450 - .550 in order that max power be obtained. We have experienced slight weakness when the throttle is closed to the slow running position. This has been improved by an extension on the slow running jet. The reason you overcome this trouble by holding up the piston 1/8" is that the taper needle is also lifted and allows a bigger supply of petrol to fill up the diffuser and the slow running well when the throttle is closed. We cannot understand however the improved acceleration obtained in this manner. We are sending a quick thread adjustment which will give you a bigger range of mixture strength. Bed tests have shown that improved acceleration can be obtained in the following manner :- (1) Blank 2 of the 6, - .039 dia top row diffuser bleed holes. (2) Blank 3 of the 6, - .055 dia bottom row of diffuser holes, then set the high speed jet in the following way. When thoroughly hot run the engine light at 1000 R.P.M. Adjust the main jet so that the engine is running with a normal mixture strength, the control being in a normal position. When put over to weak the speed should fall from 1000 to 950 R.P.M. or nearly so. | ||
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).