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).
Metering curve graph and analysis for a 20 HP carburetter.
| Identifier | WestWitteringFiles\O\2January1926-March1926\ Scan178 | |
| Date | 17th March 1926 | |
| contd :- -2- STD CARBURETTER - 20 H.P. METERING CURVE FOR GRADUALLY INCREASING LOAD UP TO 2250 R.P.M. WHEN ENGINE IS THEN FULL THROTTLE. ABOVE NORMAL LINE INDICATES WEAKNESS - BELOW RICHNESS. Graph annotations: POSN OF MIXTURE CONTROL RICH WEAK R.P.M. AIR VALVE STARTS TO LIFT. AIR PORTS JUST OPEN HIGH SPEED JET SET HERE amounting to, on an average, 3 notches on the mixture control. After the high speed jet comes into action the mixture tends to become rich up to the time that the air ports in the dash pot are uncovered. The latter trouble could easily be corrected by slightly lowering the ports but 'richening up' at this period is a distinct advantage with regard to acceleration. The disadvantage however remains that should the engine be kept running with the air valve at this particular position, its operation would tend to become erratic due to an over-rich mixture. Under actual road conditions it is found that slight over-richness is not very evident because the car is seldom operating for long at this particular depression, but for max. acceleration greater richness is desirable. On the other hand a correct mixture at this position of the air valve becomes very noticeable from the poor acceleration resulting, and is evidently caused by the lag of the high speed jet in starting to spray when the throttle is suddenly opened. contd :- | ||