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).
Tester's report on rectifying a 'luffing up' issue with a Phantom II semi-expanding carburettor.
| Identifier | ExFiles\Box 13\4\ 04-page095 | |
| Date | 31th January 1933 | |
| 87080 E.{Mr Elliott - Chief Engineer} From Hs.{Lord Ernest Hives - Chair} c. to Ry. c. to Wor.{Arthur Wormald - General Works Manager} c. to Mx.{John H Maddocks - Chief Proving Officer} c. to EP.{G. Eric Platford - Chief Quality Engineer} Hs.{Lord Ernest Hives - Chair}3/MA. 31.1.33. Copy Of Our Tester's Report Re. SEMI-EXPANDING CARB. P.II. Tests have been carried out in respect of the "Luffing up" trouble with this type of carburetter. This occurs after the throttle has been fully opened and allowed to close gently - at speeds from approx. 10-30 M.P.H. The trouble was actually a carburetter mixture weakness and had a similar effect to a temporarily switching off and on of the ignition. We found after numerous experiments that the trouble centred around the petrol level in the diffuser from which the low speed jet was fed. We proved this by feeding the low speed jet directly from the float chamber instead of from the diffuser, and absolutely cured the trouble. This of course was not desirable because it upset the carburetter in other directions, but it led us to assume that by drawing the petrol from the base of the diffuser we momentarily lowered the level in the diffuser, by drawing all the petrol into the low speed jet passage and reservoir. This had the effect of trying to run the engine on the low speed only, instead of on the diffuser and the low speed jet, hence the temporary weakness until the low speed jet reservoir and passage were full and the diffuser again filled up to its normal level. We then plugged up the low speed jet passage from the base of the diffuser and drilled 4 .055" Dia. holes round the diffuser body opposite the main slow running passage, and obtained a very definite improvement, although not a 100% cure. Our next experiment was to feed the slow running jet from a higher diffuser level and this was done by putting 3 flutes connecting up with 3 .062" Dia. holes as high up the diffuser body as possible without interfering with the air bleed holes. This actually overcame our "Luffing up" trouble but there were still definite signs of mixture weakness at 18 and 27 M.P.H. on decelerating, but we overcame this by fitting a tubular extension on the low speed jet, allowing same to protrude 1/4" into the low speed jet reservoir. Before fitting this tail however, we tried cutting out the reservoir altogether, but it impaired our acceleration. | ||