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 the cause of poor starting on the Phantom III, particularly in hot weather due to an over-rich mixture and fuel flooding.
| Identifier | ExFiles\Box 151\3\ scan0349 | |
| Date | 21th December 1937 | |
| File 1290 To Rm. {William Robotham - Chief Engineer} from RM {William Robotham - Chief Engineer} /PD. 21st. December 1937. PHANTOM III STARTABILITY. We have been investigating the cause of poor starting on the Phantom III, mainly met with in hot weather, but quite likely to be found after hard driving, and standing, so allowing the under bonnet temperature to rise, this is dealt with later. Customers apparently like to switch the ignition on and start the engine with the hand throttle in the tick-over position, on the P.III this means that the engine will be only turning at 250 R.P.M. We have found from our tests that difficult starting is mainly caused through over-rich mixture. It is fatal for the driver to depress the accelerator pedal and so operate the accelerator pump on the carburettor, and expect to start the engine with the throttle at the idle, the mixture will be too strong, and the only way to start is to open up the throttle by hand. 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 88°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 reason for this difficult starting and over rich mixture lies in the position of the carburettor and the rise in petrol level due to heat and pressure in the lines, all our tests were carried out with petrol pumps in the frame. The only way we can suggest of improving this trouble is to give the carburettor a forward bias, at present the standard position is 1.5° backward lean, which makes matters worse. | ||