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).
Letter discussing engine restart problems after testing on the Stelvio Pass, theorizing it is due to petrol evaporation.
| Identifier | ExFiles\Box 91\4\ scan0230 | |
| Date | 2nd September 1935 | |
| G.W. Hancock, Esq., Hotel de France, Chateauroux, Indre, France. Since the tests on the Stelvio I have been thinking over the phenomenon which took place on top of the Pass; i.e., that though the car would run alright to the top and would slow run passably well when it was stationary there, if the engine was stopped and the car allowed to stand for 5 or 10 minutes it was found impossible to re-start. I have come to the conclusion that this trouble is likely to be due to the fact that we balance our float chambers to the air intake, whereas on the Cadillac and the Bentley cars, which show no signs of the trouble, this is not done. It appears to me that what happens is that the petrol evaporates from the float chambers when the car is left standing and the petrol vapour so formed passes into the air intake silencer. When an attempt is made to re-start the car, the mixture in this air intake silencer is so rich that this is found to be impossible. Furthermore, fresh petrol being supplied to the float chamber will continue to evaporate and pass carburetted mixture of an over-rich strength into the air intake silencer. If the carburetter float chambers were not balanced to the air intake, I do not see what could possibly prevent the car being started, since we know that with the filter outside the frame the petrol pumps are capable of supplying petrol to the float chambers. Perhaps you will let me know if this is not so. If the petrol pumps can supply petrol to the float chambers, and the float chambers have a vent to atmosphere, then I cannot see that even if the petrol continued to boil in the float chamber it should prevent the car from being started. | ||