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).
Carburettor testing, detailing modifications to the diffuser and investigations into slow running performance.
| Identifier | ExFiles\Box 1\10\ B001_X106 TO X 110-page080 | |
| Date | 24th October 1932 | |
| -3- needle (E.100717). A complete range of needles are being made for testing out the most suitable. The smaller bore of the diffuser has been opened up from .135 diameter to .155 diameter and the four delivery holes in the diffuser head from .089 diameter to .098 diameter. These alterations have, we notice, been incorporated on the latest diffuser to Lec.3245. Section FF. on Lec.3157 shows a petrol feed to the top side of the needle guide, presumably to account for any air leaks which may occur between the needle bearing and the main jet. We find that this passage actually weakens off the mixture at the high speeds and quote figures taken at 4500 R.P.M. Consumption with passage as FF. = 45 pts/hr. " " blank = 48 pts/hr. We are going to investigate the reason for this feature by the use of an externally arranged passage. Slow Running. As received the slow running was very erratic and the effect of having the starting cock on or off made very little difference to the mixture strength. By having good fitting throttle edge plug, the above points were improved, but still the mixture did not richen as much as expected when using the starting cock, and cutting off the air supply through the small venturi. The throttle body was then made a dead fit in the carburetter casting, sealing off any possible air leaks into the annular gas passage, and we found the starting plug had considerably more effect. In view of variation in clearance between the throttle body and the carburetter casting in production, it would be if possible better to have a drilled and definite gas passage as P.II expending carburetter, cutting out the possibility of any air leaks into the system. The actual slow running is uneven at any speed below 350 R.P.M. and this may be mostly due to the camshaft, but we will test this more thoroughly as soon as possible. | ||