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).
Description of the carburetter's internal mechanism and fuel mixture control at various throttle settings.
| Identifier | ExFiles\Box 122\4\ scan0069 | |
| Date | 15th January 1935 | |
| -2- After correcting the slow running setting, the mixture appeared weak at part throttle openings and possibly this is one of the difficulties that is mentioned by General Motors. Balance between the twin carburetters is carried out by a slot in the throttle bore flange, the dimensions of which are .75" by .225" deep, whilst the main chokes are 1.00" dia. The attached sketch Hs.{Lord Ernest Hives - Chair}1709 shows two views of the internal mechanism, the operation of the carburetter being briefly as follows - One main jet is used to meter the supply to the main deliveries and the slow running feeds. Operating in a stand tube above this jet is a parallel sided needle which is attached to a small suction piston and connected to the induction pipe depression. At small throttle openings with a high depression, the piston is sucked down against a light return spring and thus carries the needle down into the jet, leaving only a very small orifice, sufficient to feed the slow running requirements. When the throttle is open the depression is low and the spring returns the piston which lifts the needle so that there is no restriction in the main jet. Petrol is thence fed into the delivery tubes which are of the diffuser type and fitted with external jets which control the amount of air bleeding. The mixture is then delivered into shrouds .375" internal dia. and extending into the main chokes. Attached to the end of these shrouds and extending the edge of the throttles when in the full open position, are wire frames formed as a U, and our only explanation of their use is that they are directional vanes for the mixture stream to overcome throttle bias. Other than the main jet supplying the diffusers there is a small fixed jet feeding into each diffuser, which only appears as an extra to the main supply. | ||