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).
Error in setting the starting carburetter pilot jet.
| Identifier | ExFiles\Box 66\3\ scan0222 | |
| Date | 27th December 1927 | |
| W Hy{Tom Haldenby - Plant Engineer} X8280 OY1.R.12.27.27 December 27th, 1927. TO Mr. Ainsworth Mr. Caswell cc - Mr. Burton Mr. Beaver Mr. Nadin(England) Mr. Bagnell Mr. Poole FROM Mr. Olley [Stamp: POST ... RECEIVED JAN 9 19...] RE STARTING CARBURETTER Section 5280 The error which we have made in setting the pilot jet is best seen by reference to attached chart. Mr. Caswell is investigating the best setting and will report shortly. To understand the chart it is necessary to consult the two prints, E22879, showing the old needle and A 8410, showing the new pilotted needle ( intro-duced by us at first Phantom chassis 1701 and now adopted by England.) The only difference in dimensions now between our jet and England's is that ours is threaded 22 per inch, and theirs 26 per inch. (Simultaneously with the introduction of the pilotted jet by England they have adopted the locknut on the adjustment which we have used since chassis 1501.) England adjusted the old jet from 3/4 turn to 1-1/2 turns back, and we used 1-1/2 to 2 turns. With the new needle England are insistent on a setting of 1/3 turn (±1/12 turn) as the correct setting. The chart shows that this corresponds in jet area to 1-3/8 turns with the old needle. Therefore, taking 1-3/4 turns as our average setting for the old jet, we should have used since 1701 a setting of about .412 turns or 148°. Instead of this we have been using the old setting of 1-1/2 to 2 turns, that is we have been using a jet opening 3 to 4 times as great as we used to have on the S. Ghost. Experience on the S. Ghost showed us that it was practically impossible to set the starting carburetter too strong if best starting was to be secured in the coldest weather, but the drains on the Phantom intake pipe are obviously less effective than the boilers on the S. Ghost, and it is obvious that we have overdone it. (Continued) | ||