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).
Testing and modification of Spectre Carburetters.
| Identifier | ExFiles\Box 93\2\ scan0079 | |
| Date | 6th September 1935 | |
| Hs{Lord Ernest Hives - Chair}/Swdl.{Len H. Swindell}25/KW.6.9.35. SpectreCodename for Phantom III Carburetters. We have tested No.10, the 10,000 miles unit, on the bed fitted with the reverse throttle carburetters LeC.4378. Other modifications on these carburetters include the top feed to the floatchambers which enables the float needles to be removed without removing the carburetters, and a separate screw on each throttle stop for slow running adjustment. The floats as fitted, E.86948/62 of 24 SWG, were too heavy and allowed practically no needle movement at the correct level setting. These were replaced by lighter floats off the original type of carburetters, E.84998/5002, which are 26 SWG, and together with deleting the tab stop E.86956 from the under side of the float, a needle movement of .040" was obtained, passing well in excess of the petrol supply required. The "changeover" position from slow running at 225-250 r.p.m. to the main jet coming in at approximately 300 r.p.m. was very weak and almost cut out. By reducing the piston stand from .175 to .100 thus increasing the depression upon the main jet; raising the LeC. petrol level by .125, and retaining the .025 dia. slow running jets, the changeover weakness was almost overcome. The mixture strength for slow running becomes much too sensitive to give a definite setting when it has such a considerable effect on the weak spot at a little higher speed. Actually the trouble is in obtaining a normal mixture strength at the changeover speed and yet not be too rich at the slow running speed. We have yet to confirm on the road whether the pivoting of the floats at 90° to the old position is affected by acceleration or braking. | ||