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).
Engine starting methods, comparing the use of pilot jets and chokers with American gasolines.
| Identifier | ExFiles\Box 50\3\ Scan061 | |
| Date | 24th May 1921 guessed | |
| Oye - G 24821 Sheet #2. These gasolines would undoubtedly foul plugs and cause carbon deposits. I think one can see from these distillation curves why pilot jets are not generally used for starting on American cars. I wrote some time ago that the probable reason for this is that the pilot jet will not give a rich enough mixture for starting cold for this to be capable of running the engine slow without wasting gasoline when it is warm. The choker, which is a more drastic means for starting the engine, seems absolutely necessary in this country under present conditions. It depends for its principle on a very high vacuum in the induction pipe and carburetter, such that as much as possible of the American gasoline is evaporated cold and the rest passing into the cylinder as a liquid, and most of it escaping into the exhaust or the crankchamber. The amount of air permitted to pass the choker is so arranged that under the coldest conditions a fairly good firing charge exists in the cylinder. The choker is used to the least possible extent by any intelligent driver in this country, because he understands that its use implies crankcase dilution, therefore he will use it full on for very short intervals of a second at a time, or he will use it half on and as the weather gets warm he will try more and more to dispense with its use altogether. This is understood by almost any intelligent American driver. If the choker is put on when the engine is running on any American car, it will stop the engine at once. The advantages over our priming device are therefore - 1. High vacuum. 2. The engine cannot be run with the choker full on. 3. A continuous supply of firing mixture is available instead of the limited supply as with the priming device. Probably a pilot jet could be made to do the work just as well with a butterfly throttle, provided that the jet were made adjustable so that it could be increased very much in richness for cold weather starting. We consider the scheme we have fitted to 4-EX is very good. It should be noted, however, that we had no time to ad-just it and therefore it is somewhat fierce in its action and probably the butterfly valve in the low speed air intake should be filed around the edges to allow more air to pass when the valve is closed. | ||