US3223391A

US3223391A - Carburetor

Info

Publication number: US3223391A
Application number: US233261A
Authority: US
Inventors: Jr Warner B Shepherd
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-10-26
Filing date: 1962-10-26
Publication date: 1965-12-14
Anticipated expiration: 1982-12-14

Description

Dec. 14, 1965 Filed Oct.

FIG

w. B. SHEPHERD, JR 3,223,391

CARBURETOR 3 SheetS Sheet 2 INVENTOP 4 (I) \Dmanaz B. $HEVHERD, JR.

w/Ml 74m ATTO EN EYS Dec. 14, 1965 w. B. SHEPHERDFJR 3,223,391

CARBURETOR Filed Oct. 26, 1962 3 Sheets-Sheet 5 QT TO ZN'EYS 3O m.p.h. with no load or acceleration demands.

United States Patent 3,223,391 CARBURETOR Warner B. Shepherd, Jr., 831 th St., Verona, Pa. Filed Oct. 26, 1962, Ser. No. 233,261 2 Claims. (Cl. 261-23) This invention relates to improved carburetors.

In conventional automotive carburation systems, fuel is Supplied to combustion chambers of an internal combustion engine by means of metering jets which feed fuel to the engine via the intake manifold thereof in proportion to venturi action caused by air being drawn through ventun'es or responsive to manifold pressure.

Conventional carburetors, as, for example, a standard multiple barrel carburetor employed primary jets as the only supply of fuel at cruising speeds below approximately Under load conditions, such as when the vehicle employing the carburetor is accelerating or climbing hills, additional fuel is supplied to the engine by a power jet normally actuated by manifold vacuum or pressure. In some cases, this powered jet is a separate jet from the primary jets, and, in other cases, includes means for increasing the effective size of the primary jet or jets. At a predetermined high speed of approximately 45 m.p.h. or over, and for maximum power demands, still another supply of fuel is furnished by secondary jet means which are normally located in separate speed throats of the carburetor. The secondary jet means are normally inoperative at low speeds whereby they close the high speed throats of the carburetor. The secondary jet means are usually operated by a combination of manifold vacuum and venturi action in the low speed throats of the carburetor. Each of the aforementioned jet or jet systems are designed to give the proper fuel-air ratio necessary to properly operate the engine under all speed, power and acceleration requirements. With all the above mentioned jets in operation at a speed of, for example, 65 m.p.h. at full load requirements, the jets are effecting a maximum supply of fuel which mixes with the amount of air being drawn in at that speed to provide a relatively rich fuel-air ratio. If the speed of the vehicle is then increased to approximately 90 m.p.h. with the throttle wide open or substantially wide open, the carburetor is supplying a substantially leaner mixture to the engine than at 65 m.p.h. This is because at wide open throttle, air is being drawn in at a rapid rate with very little restriction or friction while the rapid flow of fuel through the jets is highly restricted thereby causing an increased amount of friction which obviously retards the flow of fuel. Conversely, at intermediate speeds of say 55 m.p.h., the fuel-air ratio is at a maximum because the fiow of air through the carburetor is quite restricted while the fuel jets are not. This results in the fuel-air mixture being richer than necessary at cruising speeds thereby burning an excess amount of fuel and causing the fuel-air mixture to be quite lean at very high cruising speeds which reduces the maximum power output of the engine and often results in damage to the engine such, for example, as burning of the exhaust valves. At wide open throttle and high speeds it is desirable that the engine develop maximum power output, particularly when the engine is used for racing purposes.

It is well known that maximum power of an internal combustion engine is produced when the fuel-air mixture supplied thereto is relativelyl rich. Also, it is well known that relatively lean mixtures, particularly at high speeds and wide open throttle, may damage the parts of an internal combustion engine due to, for example, the burning of the exhaust valves of the engine, excessive pre-ignition of the fuel, etc. It is also desirable to have the fuel-air mixture supplied to an internal combustion engine at normal cruising speeds, to be relatively lean for maximum economy. However, in conventional carburetors, it is necessary that the fuel-air mixture at normal cruising speeds, be relatively rich in order that the jets of the carburetor may supply sufficient fuel at very high engine speeds.

Accordingly, it is a primary object of this invention to provide new and improved means for a carburetor, whereby the fuel to air ratio supplied by the carburetor is automatically properly regulated throughout the full range of engine speeds, whereby the fuel-air mixture is relatively lean at normal cruising speeds for maximum economy and is relatively rich at very high speeds for maximum power and engine protection.

It is still another object of this invention to provide a new and novel carburetion system effective to greatly increase the economy of engine operation by maintaining the fuel to air ratio supplied by the carburetion system at the proper ratio regardless of the speeds of engine operation.

It is still another object of this invention to provide a new and novel means whereby standard carburetors may be modified inexpensively with a minimum of conversion operations to effect a regulated carburetion control of engines through all speed ranges, and more particularly at extreme high engine speeds, at which improper carburetion control would cause serious damage to the engine and prevent the engine from producing its maximum power output.

These, together with other objects and advantages which will become subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like reference numerals refer to like parts throughout and in which:

FIG. 1 is a perspective view of a conventional four barrel carburetor modified .in accordance with the invention disclosed herein;

FIG. 2 is a diagrammatic view of the jets employed in the carburetor shown in FIG. 1;

FIG. 3 is an enlarged elevational view of the carburetor shown in FIG. 1, with portions broken away so as to show the main metering system;

FIG. 4 is an enlarged elevational view of the carburetor shown in FIG. 1 with portions broken away so as to show the idling metering system and my improved high speed metering system;

FIG. 5 is a view similar to FIG. 4, but showing the power enrichment system;

FIG. 6 is a View similar to FIGS. 4 and 5, but showing the secondary metering system;

FIG. 7 is a perspective view of the top of the carburetor in an inverted position;

FIG. 8 is an enlarged vertical cross sectional View taken through the metering jets for the high speed metering system shown in FIG. 7.

The invention is illustrated in the drawings as applied to a carburetor similar to the Holley Carburetor Model 4000 for 1955 and 1956 Fords, Lincolns, and Mercurys. However, it is to be understood that the invention could be applied to similar carburetors of a diiferent make and model.

As illustrated in FIG. 4, the carburetor 10 includes a top 12, a main body 14, and a throttle assembly 16.

The main body 14 includes a conventional float chamber 18 containing a conventional inlet valve operated by a float in the float chamber 18, not shown. The float operated valve is connected by conduit means to the fuel pump of the vehicle engine.

The throttle assembly 16 includes a throttle housing 20 provided with two vertically extending parallel

primary throttle passages

22 and 24 and two vertically extending parallel secondary or high speed throttle passages 26 and 28. A horizontal throttle shaft 30 extends diametrically through the housing and through the

primary throttle passages

22 and 24, and a secondary throttle shaft 32 extends parallel to the shaft through the secondary throttle passages 26 and 28. The

throttle shafts

30 and 32 each have secured thereto a pair of substantially

circular throttle plates

34 and 36 respectively in the primary and secondary passages. The throttle shaft 30 is connected to a conventional accelerator pedal by means of a conventional linkage, not shown, and the throttle shaft 32 as shown in FIG. 6, is connected to a pneumatic motor 38. The housing of the motor 38 is divided into an atmospheric chamber 40 and a vacuum chamber 42 by flexible diaphragm 44. The diaphragm 44 is operatively connected to the shaft 32 by means of a plate 45 secured to the shaft and a rod 46 pivotally connected at one end by means of a pin 48 to the plate and abutting the diaphragm at its other end by means of a thrust plate 50 which may be secured to the diaphragm. A coil spring 52 is compressed between one wall of the motor housing and the diaphragm so as to urge the throttle plates 36 to a closed position.

The upper ends of the

primary passages

22 and 24 and the secondary passages 26 and 28 are restricted so as to form venturi passages 54 in the primary passages and venturi passages 56 in the secondary or high speed passages. As shown in FIGS. 1 and 4, the upper ends of the venturies 56 are each formed with a flared inlet opening 58 and the venturies 54 in the primary throttle passages communicate with laterally extending passages 60 formed through one side wall of the main body 14. A pair of choke plates 62 in passages 60 are mounted on a choke shaft 64. The choke shaft 64 has one end connected to a conventional thermostatic operator which normally maintains the choke plates 62 in a closed position as illustrated in FIG. 1. After the intake manifold of the engine has been properly heated, the thermostatic operator rotates the shaft 64 and choke plates 62 to the open position illustrated in FIG. 4.

When the accelerator pedal controlling the carburetor is released, the two primary throttle plates 34 are urged by spring means, not shown, to the closed position as illustrated in FIG. 4. Atmospheric pressure acting on the fuel in the float chamber 18 forces the fuel to flow through a main jet 66 into a main well 68. From the main well 68, the fuel flows upwardly through an idling well 70, then horizontally through an idle restriction 72 and downwardly through an idle passage restriction 74 into a vertical passage 76 which terminates in a horizontally extending chamber 78. As the fuel flows through the idle restriction 72 it is mixed with air passing through an idle bleed 80. This bleed also acts as a vent to prevent any siphoning effect through the idle system at high speeds or when the engine is stopped. As the fuel flows from the chamber 78 into the passage 82, additional air enters the chamber 78 through the two idler transfer holes 84 and is mixed with the fuel. The fuel and air mixture then flows past the adjustable idler needle valve 86 which controls the mixture delivered at idle. From the idle adjusting needle chamber 88, the fuel-air mixture then flows downwardly through a short diagonal passage to a horizontally extneding groove 90 in the bottom surface of the throttle assembly 16. The groove 90 leads to a point midway between the

passages

22 and 26 to a plurality of branches whereby the fuel mixture is discharged into both the primary and

secondary passages

22 and 26 thereby ensuring an even distribution of fuel throughout the manifold at idle. An identical idle system is also provided for the primary and secondary passages 24 and 28. When the throttle plate 34 is slightly opened, fuel also begins to flow through the idle transfer holes 84 as they are exposed to manifold vacuum.

As the throttle plate is opened still wider and the engine speed increases, the air flow through the carburetor is also increased. This creates a vacuum in the venturi passages 54 strong enough to bring the main metering system shown in FIG. 3, into operation. The flow from the idle system tapers off as the main metering system begins discharging fuel whereby the two systems provide a smooth and gradual transition from idle to cruising speeds. In the area of the greatest vacuum in the throat of the primary venturi 54, a small boost venturi 92 is located. A vacuum is created within this smaller venturi which is stronger than that in the primary venturi 54, but still proportional to the air flow through the carburetor. This difference in pressure between the vacuum in the boost venturi and the normal air pressure in the float chamber 18 causes fuel to flow through the main metering system provided for each of the

primary throttle passages

22 and 24, one of which is illustrated in FIG. 3. At cruising speeds of approximately 30 mph or greater, the fuel flows from the fioat chamber 18 through the main jets 66 into the bottom of the main well 68. The fuel moves up the main well 68 through the main well tube 94 where air is spread into the fuel by small passage 96 extending radially through the side of the main well tubes and vertical-1y upwardly adjacent one side thereof. This mixture of fuel and air, being lighter than raw fuel, responds faster to any change in venturi vacuum and vaporizes more readily than raw fuel when discharged into the air stream of the venturi. As the fuel ejects from the aspirating nozzle 97 of the main well tube, additional air is mixed therewith by means of a vent 98 in the top 12. This mixture of fuel and air then moves downwardly through a passage 100 whereby it is discharged into the throat of the boost venturi 92 by means of a nozzle 102. The throttle plate 34 controls the amount of fuel-air mixture admitted to the intake manifold, thereby regulating the speed and power output of the engine in accordance with accelerator pedal movement. There are identical main metering systems in both

primary passages

22 and 24.

A transfer tube 104 is mounted adjacent the bottom edge of each boost venturi 92 whereby any excess fuel collecting on the boost venturi is sucked into the transfer tube and through a vertical passage 106 whereby the fuel is ejected into the intake manifold by means of the groove 90. The transfer tube is particularly effective during idling to withdraw any excess fuel on the boost venturi.

During high power operations, particularly at lower engine speeds, such as during acceleration, the carburetor must deliver a richer mixture than is needed when the engine is running at cruisng speed with no great power output required. The added fuel for efficient operation is supplied by the power enrichment system shown in FIG. 5 and sometimes referred to as the economizer system.

The power enrichment system is controlled by manifold vacuum, which gives an accurate indication of the power demands placed upon the engine. Manifold vacuum is strongest at idle and decreases as the load on the engine is increased. As the load on the engine is increased, the throttle plates must be opened wider to maintain any given speed. Manifold vacuum is reduced because the opened throttle plates ofier less restriction to air entering the intake manifold.

Manifold vacuum from below the primary throttle plates 34 is transmitted through a vacuum passage 108 in the throttle assembly 16, the main body 14 and top 12 to the top of the economizer diaphragm 110 in the vacuum chamber 112. Below the diaphragm 110 there is a power jet 114 located in the bottom of the float chamber 18. A valve stem 116 is connected at its upper end to the diaphragm 110 and its lower end extends through the jet 114. A tapered head 118 is secured to the lower end of the stem 116 and the upper end of the stem is slidably mounted in a plate 120 secured to the top 12. A coil spring 122 encircles the stem 116 and is compressed between the plate 120 and a radial flange on the lower end of the stern so as to normally urge the head away from the restricted openings in the power jet 114 so as to provide a metered opening therethrough. A lateral passage 124 communicates the lower portion of the power jet with each of the main wells 68.

As engine power demands are reduced, the increased vacuum acting on the diaphragm 110 overcomes the tension of spring 122 and draws the economizer diaphragm and stem 116 upwardly thereby closing the power jet 114. Conversely, when the accelerator pedal is suddenly depressed, or depressed at a relatively rapid rate, the manifold pressure increases thereby increasing the pressure in vacuum chamber 112. This increase in pressure permits the spring 122 to urge the stem 116 downwardly so as to open the power jet 114 and supply additional fuel to the main wells 68. This additional supply of fuel increases the amount of fuel flowing from the nozzles 102 thereby maintaining the fuel-air mixture furnished by the carburetor at the proper level.

At lower speeds, the secondary throttle plates 36 remain closed, allowing the engine to maintain satisfactory fuel-air velocities and distribution. When engine speeds increase to a point where additional breathing capacity is needed, the secondary throttle plates are opened by the secondary system shown in FIG. 6.

Vacuum taken from one primary venturi 54 is transmitted to the vacuum chamber 42 by means of a short passage 126, an L-shaped passage 128, a sloping passage 130 and a short passage 132. At high speeds when engine requirements approach the capacity of the two

primary bores

22 and 24, the strong primary venturi vacuum in the venturis 54 move the diaphragm 44 upwardly compression spring 52. The diaphragm 44 acting through the rod 46 and plate 45 will commence to open the secondary throttle plates 36. The amount which the secondary throttle plates are opened depends on the strength of the vacuum from the primary venturi 54. This, in' turn, is determined by the air flow through the primary bore to the engine. As air flow increase through the primary venturies, a greater secondary throttle plate opening will result and the secondary passages will supply a larger portion of the engines requirements. As the secondary throttle plates open, additional vacuum is supplied to the chamber 42 by means of a restricted passage 134 extending between one of the secondary venturis 56 and the passage 126. A ball check valve 136 in passage 130 normally rests on a seat having a restricted passage therethrough. When the primary throttles are suddenly opened, vacuum maintains the ball check valve 136 on its seat thereby restricting the rate at which air is drawn from the chamber 42 and thus preventing the secondary valve plates from being opened too rapidly.

Fuel is supplied to each of the secondary or high speed passages 26 and 28 by a separate system each of which is identical and for simplicity, only one of which is shown in FIG. 6. Each system includes a secondary jet 138 connected to the top 12 and having a tubular extension 149 extending downwardly into the bowl 18. The upper end of the jet 138 communicates with a horizontal passage 142 in the top and the outer end of this passage communicates with a diagonal passage 144 in the throttle assembly 16 by means of a vertical exterior pipe 146. The passage 144 communicates with a secondary discharge nozzle 148 and secondary transfer holes 150 in the venturi 56 and passage 26 respectively, by means of a passage 152 and check valve 154.

As the secondary throttle plates 36 begin to open, a vacuum is first created at the secondary barrels 26 and 28 and then, as air flow increases, at the secondary veuturis 56. Fuel is drawn up from the float chamber 18 through extension 140 and secondary jet 138 passed a secondary air bleed vent where air is admitted to and mixed with the fuel. The secondary air bleed vent 156 also vents the fuel passage 142 to prevent a siphoning effect when the secondary system is not in operation. The fuel and air mixture continues on down the pipe 146,

passages

144 and 152 where it is either discharged at the secondary transfer holes or the secondary discharge nozzle 148 depending on the position of throttle plate 36. Fuel is first ejected through the holes 150, but after the vacuum increases to a suflicient level at the venturi 56, the ball check valve 154 is lifted from its seat so as to permit fuel to be supplied to and discharged from the nozzle 148.

When the engine speed is reduced, there is a corresponding reduction in vacuum produced at

venturies

54 and 56 and in the vacuum chamber 42 thereby permitting the spring 52 to gradually close the secondary throttle plates 36. The secondary throttles 36 are normally opened at speeds of 45 mph. or above.

The carburetor is also supplied with a conventional accelerating pump system which includes a spring operated pump, not shown, located in a hollow projection 158 on the top 12 and a cylindrical projection 160 on the main body 14 as illustrated in FIG. 1. The accelerating pump normally supplies additional fuel through nozzles 162 at the top of the

primary passages

22 and 24.

As shown in FIG. 1 the throttle linkage is also provided with a conventional dashpot 164 to prevent the primary throttles from closing too rapidly.

The above described carburetor is of conventional construction. However, as previously explained, this conventioual carburetor structure has inherent disadvantages in that it supplies a mixture which is too rich during normal cruising speeds, thereby excessively increasing fuel consumption and at very high speeds of the engine, the mixture is too lean, thereby reducing the maximum power output of the engine. Accordingly, I propose to improve the conventional carburetor by adding thereto a high speed fuel system as illustrated in FIGS. 2, 4, 7, and 8. This high speed system includes two identical systems, one for each of the secondary or high speed passages 26 and 28. Each system includes the addition of a high speed jet 166 having a threaded upper end 168 which is threaded through a bore in the top 12. Each jet 166 has an elongated extension 170 which extends downwardly into the fuel bowl 18. The extreme upper threaded end of each jet 166 extends through the top 12 and is threaded into one end of an L-shaped elbow fitting 172. An L-shaped tubing 174 is provided for each of the elbow fittings 172. Each tubing 174 has a horizontal leg 176 extending above the top 12 and having one end connected to one elbow fitting by means of a conventional pipe coupling 178. Each tubing 174 also has a vertical leg 180 which extends downwardly and terminates within one of the secondary veuturis 56. An air bleed orifice 182 is drilled into each elbow fitting directly on the outside curve of the elbow. This orifice 182 is of such a predetermined diameter so as to prevent any venturi action in the carburetor from drawing fuel through the high speed jets 166 at all low and intermediate speeds and the lower end of the high speed range of the engine.

Since the high speed jets 166 supply additional fuel and thereby enrichen the mixture at very high engine speeds, I thereby reduce the size of the secondary jets 138. Thus, at moderate and intermediate cruising speeds of approximately 45 to 75 mph for example, the secondary jets 138 being of reduced size, provide a leaner mixture for maximum economy. At very high cruising speeds, such as 75 mph. for example, my high speed fuel system is designed to operate to supply additional fuel to the secondary passages 26 and 28 and thereby eurichen the mixture to a point where it produces maximum power and also causes the engine to operate at a cooler temperature thereby prolonging the life of the valves therein.

The air bleed orifices 182 are substantially larger than the bleed orifices 156 in the secondary fuel system, thereby ensuring that no fuel will be supplied through the high speed system except at very high speeds. It is only at very high speeds that the vacuum produced in the venturis 56 is sufficiently great to cause suflicient suction 7 within the elbow fitting 172 to suck up fuel through the high speed jets 166 from the float chamber 18. Of course, once fuel is sucked up through the high speed jets 166, this fuel mixes with air entering through the orifices 182 thereby ensuring that the fuel will be more readily vaporized once it enters the carburetor and intake manifold. Of course, as the fuel is ejected from the tubing 174 into the secondary venturis 56, it mixes with the air entering through opening 58 and this fuel and air mixture passes downwardly Where it is further enrichened by the fuel entering the secondary venturis via the secondary discharge nozzles 148.

It is also contemplated that when maximum fuel economy is desired at low and intermediate cruising speeds, that the main jets 66 for the main fuel system shown in FIG. 3 also be removed and replaced by main jets of a smaller size. Thus, through regulated variations in the size of the orifices 182 in the high speed system, with regulated variations in the size of the secondary jets 138-140, and even with variations in the size of the orifices in the primary jets, a fuel to air ratio can be obtained throughout the entire range of speeds from low speed to extremely high speeds so as to obtain maximum economy and maximum power.

By having the air bleed orifices 182 in the high speed systems, of the proper sizes, use of the high speed jets is prevented when not required, such as during moderate and low cruising speeds, and conversely, automatically permits use of the high speed jets at very high speeds and wide open throttle to supplement the secondary jets when required at very high speeds, thereby enabling an automatic wide speed range carburetion mixture for maximum economy at cruising speeds and maximum power at very high speeds. Carburetion control as provided by this invention is particularly useful for racing vehicles since it permits the engines in these vehicles to develop more power at wide open throttle and very high speeds. Also, the carburetion system provided by this invention will greatly economize fuel cost during operation of conventional vehicles.

In summary, a conventional vehicle operating with the carburetor of this invention, will operate as follows:

The main or primary jets 66 will supply fuel through a main system at low speeds such as 30 mph. or above, the secondary jets 138-140 will supply fuel at intermediate speeds such as 45 mph. and above, the high speed jets 166 will supply fuel at very high speeds such as 75 m.p.h. or above, and the power jet 114 will supply fuel as required.

As this invention may be embodied in several forms without departing from thespirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims or that form their functional as well as conjointly cooperative equivalents, are therefore intended to be embraced by those claims.

What is claimed is:

1. A carburetor comprising a body having air duct means therethrough adapted to be connected to the intake manifold of an internal combustion engine so as to supply and air-fuel mixture from said duct means to said manifold, a fuel chamber in said body, first and second venturi means in said duct means, a main fuel passage from said fuel chamber to said first venturi means, a main fuel metering jet in said main passage, a secondary fuel passage between said second venturi means and said fuel chamber, a secondary fuel metering jet in said secondary passage, said secondary fuel passage having an air vent of predetermined size in operative communication with said secondary fuel metering jet controlling the suction thereon and thereby metering the fuel therethrough, an auxiliary passage between said fuel chamber and opening into said second venturi means, a high speed jet in said auxiliary passage, said auxiliary passage having an air vent of predetermined size in operative communication with said high speed jet controlling the suction thereon and thereby metering the fuel therethrough, said last mentioned air vent being substantially larger than said first mentioned air vent to prevent venturi action of said second venturi means from drawing fuel through the high speed jet at all low and intermediate speeds of the engine, said main passage adapted to supply fuel to said first venturi means at and above low engine speeds, said secondary passage adapted to supply fuel to said second venturi means at and above intermediate engine speeds, a throttle valve in said duct downstream of said second venturi, pneumatic motor means controlling said throttle valve, and a fluid control passage connecting said pneumatic motor means to said first venturi means, whereby when a sufficient vacuum is created at said first venturi means, during high engine speeds, said throttle valve will be moved to wide open position thereby creating sufiicient vacuum at said second venturi means to cause said high speed jet to supply fuel through said auxiliary passage to said second venturi means, and said high speed jet and auxiliary passage at other engine speeds remaining inactive.

2. The carburetor as defined in claim 1, wherein said auxiliary passage has an angular bend and said air vent opening being in the other side of said angular bend.

References Cited by the Examiner UNITED STATES PATENTS 2,114,970 4/ 1938 Rullison et al. 2,208,702 7/ 1940 Read 26169 2,715,522 8/1955 Carlson et al. 26l52 2,890,031 6/1959 Carlson et al. 2614l OTHER REFERENCES 1956 Ford Car Shop Manual: Ford Motor Company, Dearborn, Michigan, copyright 1955, pages to 100.

HARRY B. THORNTON, Primary Examiner. RONALD R. WEAVER, Assistant Examiner.

Claims

1. A CARBURETOR COMPRISING A BODY HAVING AIR DUCT MEANS THERETHROUGH ADAPTED TO BE CONNECTED TO THE INTAKE MANIFOLD OF AN INTERNAL COMBUSTION ENGINE SO AS TO SUPPLY AND AIR-FUEL MIXTURE FROM SAID DUCT MEANS TO SAID MANIFOLD, A FUEL CHAMBER IN SAID BODY, FIRST AND SECOND VENTURI MEANS IN SAID DUCT MEANS, A MAIN FUEL PASSAGE FROM SAID FUEL CHAMBER TO SAID FIRST VENTURI MEANS, A MAIN FUEL METERING JET IN SAID MAIN PASSAGE, A SECONDARY FUEL PASSAGE BETWEEN SAID SECOND VENTURI MEANS AND SAID FUEL CHAMBER, A SECONDARY FUEL METERING JET IN SAID SECONDARY PASSAGE, A SECONDARY FUEL PASSAGE HAVING AN AIR VENT OF PREDETERMINED SIZE IN OPERATIVE COMMUNICATION WITH SAID SECONDARY FUEL METERING JET CONTROLLING THE SUCTION THEREON AND THEREBY METERING THE FUEL THERETHROUGH, AN AUXILIARY PASSAGE BETWEEN SAID FUEL CHAMBER AND OPENING INTO SAID SECOND VENTURI MEANS, A HIGH SPEED JET IN SAID AUXILIARY PASSAGE, SAID AUXILIARY PASSAGE HAVING AN AIR VENT OF PREDETERMINED SIZE IN OPERATIVE COMMUNICATION WITH SAID HIGH SPEED JET CONTROLLING THE SUCTION THEREON AND THEREBY METERING THE FUEL THERETHROUGH, SAID LAST MENTIONED AIR VENT BEING SUBSTANTIALLY LARGER THAN SAID FIRST MENTIONED AIR VENT TO PREVENT VENTURI ACTION OF SAID SECOND VENTURI MEANS FROM DRAWING FUEL THROUGH THE HIGH SPEED JET AT ALL LOW AND INTERMEDIATE SPEEDS OF THE ENGINE, SAID MAIN PASSAGE ADAPTED TO SUPPLY FUEL TO SAID FIRST VENTURI MEANS AT AND ABOVE LOW ENGINE SPEEDS, SAID SECONDARY PASSAGE ADAPTED TO SUPPLY FUEL TO SAID SECOND VENTURI MEANS AT AND ABOVE INTERMEDIATE ENGINE SPEEDS, A THROTTLE VALVE IN SAID DUCT DOWNSTREAM OF SAID SECOND VENTURI, PNEUMATIC MOTOR MEANS CONTROLLING SAID THROTTLE VALVE, AND A FLUID CONTROL PASSAGE CONNECTING SAID PNEUMATIC MOTOR MEANS TO SAID FIRST VENTURI MEANS, WHEREBY WHEN A SUFFICIENT VACUUM IS CREATED AT SAID FIRST VENTURI MEANS, DURING HIGH ENGINE SPEEDS, SAID THROTTLE VALVE WILL BE MOVED TO WIDE OPEN POSITION THEREBY CREATING SUFFICIENT VACUUM AT SAID SECOND VENTURI MEANS TO CAUSE SAID HIGH SPEED JET TO SUPPLY FUEL THROUGH SAID AUXILIARY PASSAGE TO SAID SECOND VENTURI MEANS, AND SAID HIGH SPEED JET AND AUXILIARY PASSAGE AT OTHER ENGINE SPEEDS REMAINING INACTIVE.