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).
Investigation into poor starting (startability) issues on the Phantom III model due to flooding.
| Identifier | ExFiles\Box 151\3\ scan0357 | |
| Date | 14th January 1938 | |
| Rm. {William Robotham - Chief Engineer} from Rm {William Robotham - Chief Engineer} /FD. {Frank Dodd - Bodies} Rm {William Robotham - Chief Engineer} /EHB/R.14.1.38. P.III - STARTABILITY. We have been investigating the cause of poor starting on the P.III, mainly met with in hot weather, but quite likely to be found when starting up after hard driving, or a lot of traffic work. After standing, the under bonnet temperature rises, this has the effect of increasing the petrol level in the float chamber, and if the car is standing on a gradient will cause flooding, hence difficult starting. Many customers apparently make a habit of starting the engine with the hand-throttle set in the tick-over position, on the P.III this means that the engine will be only turning over at, approx. 250 R.P.M., this engine speed we consider too slow, and we strongly recommend that all P.III should be set to idle at 350 R.P.M. which gives 8.m.p.h. in the direct gear. This, together with the carburetter modification which we mention later, should materially help the starter, and flywheel teeth, the customer getting a more positive start, instead of repeatedly pressing the starter switch. Dealing with the customer who is in the habit of starting at tick-over speeds, he will experience trouble when starting on a gradient exceeding 1 in 15 if the under bonnet temperature is in the region of 68°C, the reason for this is that the temperature in the petrol lines causes a pressure to build up, and increases the petrol level in the floatchamber, hence flooding. Apart from the question of high temperature we cannot start under normal running conditions, i.e. 76°C under bonnet temperature, at idle speeds, on gradients exceeding 1 in 12.35, because of flooding; it is understood, of course, that starts can always be made with wider throttle openings. The only way we can suggest of improving this trouble is to give the carburetter a forward bias, at present the standard position is 1.5° backward lean, which makes matters worse. We have carried out tests on 36-EX with a taper packing fitted, giving the carburetter a forward bias of 3½°. Allowing for the 1½° backward lean at present standard, this means a total taper of 5° forward lean, and the float level is altered to suit the new position. | ||