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).
Analysis of carburetter flooding issues and potential fire risks on a Bentley Chassis.
| Identifier | ExFiles\Box 3\6\ 06-page159 | |
| Date | 3rd May 1934 | |
| Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} E.{Mr Elliott - Chief Engineer} BY.13/G.3.5.34. File BENTLEY CHASSIS. Referring to Wor.{Arthur Wormald - General Works Manager}2/R.2.5.34. and C.23/C.1.5.34. attached to same, the trouble in question can be co-related with two main factors :- (a). The S.U. carburetter design embodies a definite fault inasmuch as flooding of the carburetter permits petrol to escape from two or three places, and in fact it would appear that when the needle valve is not seating due to some fault, sticking etc. the action of the pump may actually cause petrol to spray out round the flooding mechanism which is provided to depress the float. (b). It would appear that under certain conditions the flooding can be so serious, judging from the two instances which have occurred as to produce a strongly explosive mixture under the bonnet. The flooding of the carburetter as described above will not cause a fire unless there is a blow back from the engine through the carburetter or sparking occurring from some of the ignition leads, but in our case a blow back could not cause a fire owing to the design of the air intake, therefore it appears to me that when the engine is turning over cold there may be a spark jump across one of the plugs to the body of the cylinder. One other possible source of ignition for the loose mixture under the bonnet might possibly be that the petrol escaping from the plunger on the top of the float chamber might spray over the distributor, when it would work in through the gauze, and if it fired there is a small hole underneath the distributor mechanism in the aluminium casting through which the flame could pass out into the free mixture under the bonnet. Conceivably as Sft.{Mr Swift} points out this hole might in itself be a danger point. I think that all the above points require investigation in order to find out precisely under what conditions the fire can be started, as two instances occurring with only about 100 chassis running certainly appears to indicate that there is a natural tendency for fire to take place when flooding of the | ||