Ihas:come to be regarded as a matter of course that the carburetter setting for power and speed must be quite different to that which is required when the aim is economical running ; the same effect will not give the best results in both directions. Most track and trial enthusiasts tune for power and leave fuel economy entirely out of the question. They may do so reluctantly, but they do it. In view of this fact, more than usual interest centres in a carburetter which definitely gives more miles per hour, and at the same time, quite automatically, as it would seem, effects an important reduction in petrol consumption.
Racing Cars fitted with the Memini.
These are the claims made for the Mernini carburetter, and they appear to be substantiated in actual practice, as is testified by quite a number of people well known for their experience and progress in the world of automobile sports. Mr. J. A. Benj afield, for example, who won the Long Handicap at the Essex Motor Club Meeting at Brooklands on the 4th of this month, says that equipping his Bentley with a couple of Memini carburetters gave him an extra two miles per hour. Mr. C. G. Coe, who is also well known to our readers, fitted one of these carburetters quite recently to his 39-98 Vauxhall-Wensum, and on the very next day won the 90 m.p.h. Long Handicap and ran to second place in the roo m.p.h. Short Handicap at Brooklands.
The carburetter, he says, although subject to little more than preliminary tuning, improved the maximum speed of his car as well as its acceleration. He states that the claims made for these carburetters are more than justified.
Mr. Woolf Barnato is sure he gets 200 revolutions per minute more on his Wolseley with a Memini than he has been able to with any other carburetter, and he believes that the Memini is mainly responsible for his getting first and second at the Brooklands Meeting on the r3th ult.
We have had this carburetter under our observation indirectly for some time, and have been marking its steady progress in the favour of the racing car owner. The time seems ripe for inquiring into its method of operation, to discover by what means these favourable results are obtained.
First Principles of Carburation.
As a preliminary, it should be pointed out, for the benefit of those who are not au fait with the principle of carburation, that the primary difficulty in providing a satisfactory mixture at all speeds, arises from the cause that with a single jet of given size and a simple choke, the actual tendency of the mixture is to grow richer as the suction increases. This is exactly the opposite to what is desired, and happens because petrol in such circumstances flows more readily than air. The difficulty has been partly overcome by the employment of pilot jets and similar devices, which operate
to enrich the mixture for starting and cease to act when the normal speed of the engine is reached.
The use of pilot jets in this way, however, brings about another difficulty, which has not yet been successfully overcome. It should be appreciated that, as the throttle is opened, the pilot automatically ceases to act, and the main jet comes into operation. If the throttle is opened slowly, no trouble arises, but if, as is invariably the case when racing, rapid acceleration is desired, and the throttle is suddenly opened to the full extent, to afford that acceleration, then the pilot goes out of action before the main jet has time to get into operation. The result is a peculiar choking, frequently referred to either in that way, or as a ” flat spot.”
The Use of a Pilot Jet.
All sorts of devices have been introduced, by various people, to improve the functioning of existing carburetters, but even so, we still have to endure, in the majority of cases, what is nothing more or less than a compromise. A carburetter must be set either to give a mixture which is comparatively rich over the whole range,—this is the best setting for power, or which, while giving a mixture which is rich enough at easy running speeds, is rather too weak to afford much power at medium speeds when the throttle valve is sufficiently wide open to have placed the pilot jet out of action, but not enough to provide a strong suction round the jet. There is a want of balance in the mixture, as considered over a reasonably extensive range of throttle openings and engine speeds.
The Memini Carburetter.