US3174732A

US3174732A - Carburetor

Info

Publication number: US3174732A
Application number: US226950A
Authority: US
Inventors: Morris C Brown
Original assignee: ACF Industries Inc
Current assignee: ACF Industries Inc
Priority date: 1962-09-28
Filing date: 1962-09-28
Publication date: 1965-03-23
Anticipated expiration: 1982-03-23

Description

March 23, 1955 M. c. BROWN 3,74,732

CARBURETOR Filed Sept. 28. 1962 fr Y r 33 374745 4q QHSS INVENTOR. MORRIS c. BRO N United States Patent O 3,174,732 CARBURETOR Morris C. Brown, St. Louis, Mo., assigner to ACF Industries, Incorporated, New `iZork, NSY., a corporation of New Jersey Filed Sept. 28, 1962, Ser. No. 226,950 3 Claims. (Cl. 251-69) This invention relates to carburetors, and more particularly to carburetors of the diaphragm type, by which is meant a carburetor as to which delivery of fuel to a fuel chamber of the carburetor is controlled by a diaphragm, as distinguished frombeing controlled by a float.

The invention is particularly applicable to a small dia phragmetype carburetor for small internal combustion engines such as are used in portable tools (chain saws, for example), in lawn mowers, small automotive vehicles such as are sometimes called go-carts, etc.

A diaphragm-type carburetor generally comprises a mixture conduit in which fuel is mixed with air for delivery to the intake manifold of an engine, a fuel chamber closed by a diaphragm and communicating through a no2- zle with the mixture conduit for delivery of fuel thereto, and valve means controlled by the diaphragm for controlling delivery of fuel from a fuel tank to the fuel chamber. An air filter is provided for cleaning air entering the mixture conduit. The mixture conduit is formed with a restriction, .e.g., a venturi. With the engine in operation, air iiows through the mixture conduit, a pressure drop occurs across the venturi (meaning that there is a partial vacuum in the venturi), and pressure on the outside of the diaphragm causes the diaphragm to flex inward and effect delivery of fuel through the nozzle (usually located at the throat of the venturi where the pressure drop is a maximum) and to effect opening lof the valve means for delivery of fuel to the fuel chamber.

A problem in prior carburetors of the class described has been control of the diaphragm for maintenance of a balanced air and fuel ratio as the air filter becomes clogged with dirt. Use of an inside vent, which interconnects a diaphragm control chamber to the carburetor inlet inside the air filter is not completely effective to maintain the air and fuel ratio in balance as the air filter becomes increasingly clogged.

Accordingly, it is the principal object of this invention to provide a vent system, particularly for a carburetor of the class described, of the full inside vent type which functions effectively to maintain a predetermined air and fuel ratio regardless of air filter clogging. in general, the vent system of this invention accomplishes this result by sensing the changes caused by the air filter becoming increasingly clogged. The invention provides a means for sensing the pressure drop across the carburetor venturi in the mixture conduit, and subjecting the diaphragm to a pressure representing a balance of pressure drops in the mixture conduit. Other objects and features will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the constructions hereinafter described, the scope of the invention being indicated in the following claims.

In the accompanying drawings, in which one of various possible embodiments of the invention is illustrated,

FIG. 1 is a longitudinal section of a diaphragm-type carburetor showing a vent system of this invention;

FIG. 2 is a transverse section taken on line 2 2 of FIG. l; and

FIG. 3 is a fragmentary transverse section taken on line 3 3 of FiG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring to the drawings, a carburetor constructed in accordance with this invention, and generally designated ice 1, is shown to comprise a main body 3 formed to provide a mixture conduit 5 extending therethrough from one end to the other. As appears in FIG. 1, the mixture conduit 5 is formed to have a cylindric throttle section or bore 7 toward one end, an intermediate restricted section 9 of venturi form, and an inlet section 11 toward its other end. The latter is generally cylindric, but with a flat as indicated at 13. The throat (the region of smallest cross section) of the venturi section 9 is indicated at 15. Body 3 has a flange 17 at the said one end of the mixture conduit (which constitutes its downstream end) for attaching the carburetor to the intake manifold 19 of an internal combustion engine as appears in FIG. l, the flange being pprovided with suitable bolt holes (not shown) for receiving bolts extending from the intake manifold for this purpose.

An air filter 21 is attached in suitable manner to the body 3 at the upstream end of the mixture conduit. As appears in FIG. l, this air filter is of a type comprising a casing 23 containing an annular filter element 25. The hole in the center of the filter element is indicated at 27. This hole is aligned with the mixture conduit 5. Air enters the filter peripherally, as indicated by the arrows in FIG. 1, tiows through the filter element to the hole 27, and thence through the mixture conduit during the operation of the engine.

Body 3 is formed with a shallow recess 29 of circular outline in one side thereof (its bottom side as appears in the drawings). This recess, which constitutes a fuel charnber, has its center generally in the plane of the venturi throat 15, and is closed by a flexible diaphragm 31 (made of fuel-resistant synthetic rubber, for example). The margin of the diaphragm 31 is clamped against the body by a cover 33, fastened to the body by screws as indicated at 35. Cover 33 is recessed as indicated at 37 to provide a diaphragm control chamber on the outside of the diaphragm. A gasket 39 is interposed between the margin of the diaphragm and the cover to seal chamber 37 from the outside atmosphere. The central portion of the diaphragm is maintained substantially flat and rigid by a pair of flat spoked wheel-

like backing members

41 and 43 lying on opposite faces of the diaphragm, and held in assembly with the diaphragm by a rivet 4S having its shank entered in a center hole in the diaphragm and center holes in

members

41 and 43. The inner end head of the rivet is in the form of a button 47 for engagement by one end of a valve-actuating lever 49.

Fuel is adapted to be supplied to fuel chamber 29 from a fuel tank 51 as shown in FIG. 2, the carburetor including fuel pump means as generally indicated at 53 for pumping fuel to chamber 29, and a needle valve 55 controlled by the aforementioned lever 49 for controlling delivery of fuel to the fuel chamber 29. For purposes of providing the fuel pump means, body 3 is formed with a shallow circular recess S7 constituting a pulsation chamber in the side thereof (its top side as shown) opposite the chamber 29 and, laterally offset from this recess 57, with an annular cavity 59 surrounding a boss 61. Recess 57 and cavity 59 are closed by a exible pump diaphragm 63 (made of fuel-resistant synthetic rubber, for example) clamped against the body all around the recess 57 and the cavity 69 by a pump cap 65. The latter is fastened to the body by screws as indicated at 67. It has a recess 69 constituting a pumping chamber on the opposite side of the diaphragm from recess or pulsation chamber S7.

The pump cap is formed with an upwardly extending boss 71 having a horizontal hole 73 extending inward from one side of the carburetor and a vertical hole '75 extending down from the inner end of hole 73 to the pumping chamber 69. Holes 73 and 75 together constitute a fuel inlet passage. A nipple 77 pressed in the end of hole 73 is adapted for connection of a fuel line 78 leading from the fuel tank 51. The pump cap is also formed with an outlet dome 79 which opens upward from pumping chamber 57 alongsideY hole 75, from which there is an inclined outlet passage 81 to a cavity 83 in the pump cap on the opposite side of pump diaphragm '63 from the annular cavity 59. From the pulsation chamber 57 there is a passage 85 through the body 3 of the carburetor for communication between the intake manifold 19 and pulsation chamber 57. A reed valve (not shown) normally closes conduit and passage 85 during the exhaust cycle of the engine. Pressure pulsations inthe intake manifold are transmitted through passage 85 to chamber 57 and cause flexing of pump diaphragm 63. Fuel is thereby drawn into pumping chamber 69 from tank 51V through inlet passage 73, 75 on downstrokes of diaphragm 63 and forced out of pumping chamber 69 on upstrokes of the diaphragm 63 through outlet chamber 79 and outlet pasisage 81 under control of apper-type inlet and outlet check valves'87 and 89. These are formed by C-shaped cuts in av valve member consisting of a disk 91 of fuelresistant synthetic rubber, for example, held in place by a retainer 93. The inlet iiapper valve 87 flexes down to open when diaphragm 63 flexes down (outlet check S9 then being closed), and iiexes to close off the lower end of hole 75 when diaphragm 63 flexes up. The outlet flapper valve 89 iiexes up to open when diaphragm 63 flexes up (inlet check 87 then being closed) and iiexes down to close off on outlet hole 94 in retainer 93 when diaphragm 63 exes down.

Body 3 has a cylindric pocket 95 extending up from fuel chamber 29 alongside the mixture conduit 5, this pocket being aligned with the aforementioned boss 61. A passage 97 extends down through the boss`61 and the body 3 to the upper end of the recess 95. A flanged tubular fitting 96 pressed in the upper end of passage 97 holds down the pump diaphragm'63. A tubular cylindric needle valve body 99 is received in recess 95, being held in recess 95 by a screw-threaded fitting 191 threaded in the lower end of this recess. The needle valve body'99 has an upper end head 103 provided with anl axial bore 105 forming a continuation of passage 97. A resilient valve seat 107, consisting of a disk of fuel-resistant synthetic rubber, Vfor example, having a center hole, is yretained at the bottom ofthe head 103 as by a ring 109 pressed into the needle valve body. The latter has a reduced extension 111 from the upper end of head 93 having an annular groove receiving an O-ring 113 for sealing against body 3 at the upper end of recess 95.

Fitting 101 has a central opening slidably receiving the stern of needle valve 55, the latter having a tapered nose 115 at its upper end for engagement with valve seat 107. The opening in the fitting is formed for flow of fuel therethrough around the stem of the needle valve. A coil compression spring 117 surrounding the Vneedle valve reacts from the lower end of retainer 101 againsta collar 119 on the needle valve to bias the needle valve to a closed position engaging the valve seat 107. The needle valve Y has anannular groove 121 at its lower end providing a lower end head 123on the needle valve. The valve-actuating lever 49 comprises a metal strip bent as .indicated at 125 .to form an upwardlytopening loop.Y Lever 49 is pivoted intermediate its ends on a pivot pin 127 received in loop 125` This pin extends parallel to the axis of the mixture conduit 5 across an upward extension 29a of the fuel chamber 29. Lever 49 thus extends laterally in respect to the carburetor and has its inner endl overlying button 47 on the control diaphragm 31. The outer end Yof the lever is forked as indicated at 129 and straddles the needle valve within the groove 121 above the lower end head 123 of the needle valve.

A throttle shaft 131 is journalled in body 3 extending laterally across throttle bore 7 of the mixture conduit 5'.

4 one end. A choke shaft 137 is journalled in body 3 extending laterally across the inlet section 11 of mixture conduit 5. Shaft 137 carries a choke 139 constituted by a sheet metal plate, and, as will beunderstood, has an operating arm (not shown) on one end.

Body 3 is formed with a hole Y141 extending upV from fuel chamber 29 to mixture conduit 5, Vthis hole being concentric with the fuel chamber and in the plane of the venturi throat 15. It is stepped, having an enlarged lower portion 143. A nozzle is received in this hole. This nozzle comprises a tubular element having an enlarged lower portion 147 of outside diameter corresponding to the diameter of the upper portion of hole 141, this lower portion being pressed into the upper portion of the hole.

At the lower end of theV nozzle is a flange 149 which seats againstthe body 3 Varound the lower end of hole 141 for sealing the lower end of the hole from fuel chamber 29. The lower end of the nozzle is plugged as indicated at 151. The tip of the nozzle extends up into the venturi throat 15.

Body 3 has a cavity 155 extending up from fuel chamber 29 alongside hole 141 on the side thereof opposite the needle valve pocket 95. This is intersected by a lateral horizontal hole 157 which at its inner end is in communication with the annular space around the lower portion 147 of the nozzle in the lower portion 143 of hole 141 via an orifice 159. The lower portion 147 of the nozzle has ports 161 for communication from this annular space to the interior of the nozzle above plug 151. Cavity 155, hole 157, orifice 159, the stated annular space, ports 161 and the passage in nozzle 145 constitute the high speed fuelcircuit of the carburetor, fuel being adapted to ow therethrough from fuel chamber 29 to the mixture conduit 5 upon opening throttle 133 and resultant flow of air through the mixture conduit. The flow is adapted to be metered by a high speed circuit adjusting screw 163 threaded in hole 157 and having a small-diameter pointed-end extension 165 reaching to the orifice 159.

Downstream from hole 141, body 3 has a cavity 167 (see FIGS. `1 and 3) in the central longitudinal plane of the mixture conduit 5 extending up from fuel chamber 29. An idle fuel port 169 opens from the upper end of this cavity into the mixture conduit 5 downstream from thek closed throttle 133. Idle air bleed holes 171 open into the upper end of this cavity from the mixture conduit upstream from the closed throttle. The lower end of cavity 167 is closed by a plug 173.V Body 3 has a .cavity 175 extending Vup from fuel chamber 29 alongside cavity167. Cavity 175 is intersected by a lateral horizontal hole 177 which at itsinner end is in communication with cavity 167 via an oriiice 179. Cavity 175, hole 177, orifice 179, cavity 167 and port 169 constitute the low speed or idle fuel circuit of the carburetor, fuel being adapted to flow therethrough from fuel chamber 29 to the mixture conduit 5, air mixing with the fuel via ports 171. The ow of idle fuel is adapted to bemetered by an idle adjusting screw 181 threaded in hole 177 and havingY a small-diameter.pointed-end extension 183 reaching to the orifice 179.

Body 3 has a Ypassage 185 extending down from they mixture conduit 5 adjacent to its upstream end to the bottom of the body. Passage V185 communicates with the diaphragm control chamber 37 through a hole 1857V Yin the diaphragm 31, and passage 189 in the diaphragm cover 33.

Body 3 also has an inclined passage 191 extending from passage 185 to the annular space 193 formed between nozzle 145 and the wall of aperture 141. The outer end of passage 191 is closed by `a plug 195. A restriction 199 is pressed in the lower end of passage `185below the intersectionofV passage 191. A second restriction 192 is positioned in passage 191. Restriction 199V is'to dampen the effect of the engine pulsations in the mixture `conduit 5. f

In operation, cranking of the engine pumps air through the mixture conduit 5 of the carburetor into the intake manifold of the engine. Flow of air past the main fuel nozzle 145 with the throttle valve 133 open provides a subatmospheric pressure at the mouth of nozzle 145 due to the venturi effect of the restriction of throat 15. This low pressure at the mouth of nozzle 145 is transferred baclr through

passage

161, 143, 159, 157 and 155 to the fuel chamber 29a. Lowering the pressure in chamber 29a causes air pressure from passage 185 on the outer surface of diaphragm 31 to press the diaphragm inwardly or upwardly, as viewed in FIGURE 2, and to rock the valve lever 49 in a clock-wise direction. This positively pulls the needle valve 55 downwardly and the end 115 of needle valve olf of the resilient valve seat 107.

Pulsations in the crankcase of the engine are transferred through passage to the pulsation chamber 57. The pumping diaphragm 63 llexes back and forth under the effect of the engine pulsations in pulsation chamber 57. This causes a pumping action in the pumping chamber 69 which sucks fuel from tank 51 through the conduit 78 into the inlet chamber 73 of the carburetor cap 65. Fuel passes into the pumping chamber 69 and out past the outlet check valve 89 into the passages 81, 83 and 105. Continual pumping forces fuel down past the open valve into the fuel chamber 25a and out through the main fuel passage to the nozzle 145.

The capacity of the pump section of the carburetor supplies fuel at a higher rate than used by the engine. Accordingly, fuel accumulates in the fuel chamber 29a to lill it and the fuel reacts against the diaphragm 31 to move it outwardly against air pressure in the control chamber 37. The valve spring 117, as the diaphragm moves away from lever 49, forces the needle upwardly into a closed position in seat 107. In fuel chamber 29a, the fuel pressure within the chamber and the valve spring 117 work together against the air pressure in chamber 37 on the other surface of the diaphragm 31. The fuel pressure in the fuel chamber 29a varies within a small range of values to open and close the needle valve 55.

An idling or low speed operation of the engine takes place when the throttle 133 is closed. At this time, there is insufficient air iow through the carburetor conduit 5 to pull fuel from chamber 29a through the nozzle 145. However, the manifold pressure downstream of throttle 133 is at subatmospheric pressure and a large pressure depression is created at the idle jet opening 169, which pulls fuel from the fuel chamber 29a through the low speed circuit. Simultaneously sufhcient air for mixing with this fuel and to operate the engine at low speed is sucked through the idle ports 171 upstream of the closed throttle 34. This air is pulled into the idle fuel chamber 157 to mix with the fuel coming from the fuel chamber 29a. Adjustment of screw 181 is used to provide the optimum fuel and air mixture for idling or low speed conditions.

The diaphragm 31 and the lever 49 together with the valve 55 constitute a fuel pressure regulator such that the fuel in the chamber 29 is retained substantially at a constant pressure during engine operation. Therefore the liow of fuel through the main nozzle 145 is proportional to the pressure differential between the fuel pressure in fuel chamber 29 and the air pressure at the venturi skirt portion 15. Since the fuel pressure in chamber 29 is maintained substantially constant, this pressure differential is controlled by the iiow of air through the venturi 9 of the carburetor and is proportional to the rate of air flow through the mixture passage 5.

The fuel pressure in chamber 29 is determined by the balanced forces on opposite sides of the diaphragm 31. In the position of the carburetor as viewed in FIG. 2, the diaphragm assembly is pressed downwardly by the weight and the pressure of fuel in chamber 29, the Weight of the diaphragm assembly, the unbalanced weight of lever 49, the force exerted by the Valve spring 117 on needle 55 and the weight of the inlet needle 55. These downward forces are balanced only by the upward pressure of air in the control chamber 37. The air pressure in the control chamber 37 is substantially that in the inlet portion of the air conduit 5 where the air passage 185 opens into the mixture conduit. This pressure must be greater than that of the fuel in chamber 29, which is determined by the pressures created by air ow through venturi 9 or idle chamber 167. When the air filter 25 is clean, this air pressure in passage 185 is slightly less than atmospheric due to the drop in pressure caused by the slight restriction offered by the air filter 25. As the filter becomes clogged with dirt due to usage, the drop in air pressure across the filter becomes greater so that the pressure within passage drops farther below that of atmospheric. The passage 185 tends to sense the true air pressure within the entrance to the mixture conduit 5 rather than atmospheric pressure. This drop of air pressure 'within conduit 5 is also sensed at the nozzle 145 tending to create a greater flow of fuel out of the nozzle. However, this effect is compensated by the corresponding drop in pressure in chamber 37 which tends to lean the fuel ow through nozzle by moving the valve 55 to a more closed position.

As the engine is operated at higher speeds with the opening of the throttle, the static air pressure in passage 135 remains substantially constant and the flow of fuel through nozzle 145 is proportional to the drop of pressure in the venturi 9. Since at low speeds, fuel flow through nozzle 145 is adjusted by needle 163 to provide a relatively rich mixture, the mixture retains its rich air to fuel ratio at higher speeds. lt has been found advantageous to lean out the air and fuel mixture as the throttle opens from its lower speed or idle position as shown in FIG. 2. In accordance With the invention, then, the passage 191 is provided between the annular space 153, formed in the surface of the venturi 9, and the air passage 155. This passage 191 permits a sensing within the chamber 37 of the pressure conditions in the venturi. A first predetermined restriction 192 is placed within the passage 191 and a second predetermined restriction 197 is placed within pasage 15 to controllably adjust the pressure in chamber 37. The restriction 199 enables an appropriate fraction of the venturi pressure to be sensed in the control chamber 37 and thus to effect variations in pressure within the control chamber in accordance with the ow conditions at the venturi. ln this manner, the pressure in chamber 37 is reduced in proportion to the amount of air flow through venturi 9. A drop in pressure in chamber 37 as the throttle is opened up causes movement of inlet valve 55 toward a closed position to reduce fuel flow through chamber 29. The pressure in chamber 37 is thus a more accurate sensing of the engines needs and leans out the mixture ow through carburetor at speeds above closed throttle conditions. As the throttle is moved from its wide open position to its closed position, the venturi pressure in the skirt region 15 increases a corresponding amount and is sensed through passage 191 in chamber 37 to enrichen the air and -fuel mixture ratio, accordingly. With closed throttle and with a no flow of fuel through the venturi, the passage 191 shows little or no difference in pressure from that in passage and accordingly is thus not eifective during this condition of engine operation.

Therefore, in accordance with the invention there is provided a modifying passage 191 connecting the control passage 185 of chamber 37 with the venturi skirt surface 15. As described above, this provides a proper sensing of the pressure conditions adjacent to the nozzle 145 so that the same pressure acting on the nozzle 145 to draw fuel through the main fuel passages is also operative to control the pressure within chamber 37 and thus modify the fuel flow through nozzle 145 according to the changes in engine operation. Thus, instead of controlling the operation of the diaphragm 31 only by the static pressure air/4free Y at the entrance to the mixture conduit immediately adjacent to the air filter 25, an additionalvcontrol is used to provide a signal which senses the ,pressure conditions at the nozzle 145. This reflects more accurately the pressure conditions in the venturi which are operative on the nozzle and provides Va more optimum air/fuel mixture during all conditions of engine operation. i

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions Without departing from the scope of the invention, it is intended that a-ll matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limitM ing sense.

What is claimed is:

l. A carburetor comprising a body, a fuel and air mixture conduit through said body, said body formed with a fuel chamber, said mixture conduit having an inlet and an outlet and a restricted portion intermediate said inlet and outlet, a fuel inlet and a fuel passage extending from said fuel inlet to said fuel chamber, an inlet valve in said fuel passage between said fuel inlet and said fuel chamber, a main fuel nozzle within said conduit restricted portion, said body having an annular space around the nozzle openinginto said restricted portion, said body having a fuel connection from said fuel chamber to said main fuel nozzle, means for operating said inlet valve, said operating means including a diaphragm operatively connected to said inlet valve and sealed at its periphery to said body across said fuel chamber to form a Wall thereof,

. 8 4 f. spring means biasing said inlet valve in a valve closing direction and said diaphragm in a direction to enlarge said fuel chamber, means forming la single closed air chamber enclosing the side of said diaphragm opposite to said fuel chamber, said bodyV including a first passage connecting said mixture conduit inlet to said air chamber whereby said diaphragm is responsive to conduit inlet airV pressure to maintain fuel in said fuel chamber at a constant pressure, and a second passage in said body interconnecting said annular space and said first passage whereby said diaphragm is responsive to the drop in air pressure at said conduit restrictive portion to vary the constant` pressure of fuel in said fuel chamber directly in response to changes of air pressure at said nozzle.

2. A carburetor as set forth in claim 1 wherein said second passage has `a restriction therein.

3. A carburetor asset forth in claim l wherein said first passage has a restriction therein between said second passage and said inlet.

References Cited by the Examiner UNlTED STATES PATENTS HARRY B. THORNTON, Pinmry Examiner.

HERERT L. MARTN, Examiner.

Claims

1. A CARBURETOR COMPRISING A BODY, A FUEL AND AIR MIXTURE CONDUIT THROUGH SAID BODY, SAID BODY FORMED WITH A FUEL CHAMBER, SAID MIXTURE CONDUIT HAVING AN INLET AND AN OUTLET AND A RESTRICTED PORTION INTERMEDIATE SAID INLET AND OUTLET, A FUEL INLET AND A FUEL PASSAGE EXTENDING FROM SAID FUEL INLET TO SAID FUEL CHAMBER, AN INLET VALVE IN SAID FUEL PASSAGE BETWEEN SAID FUEL INLET AND SAID FUEL CHAMBER, A MAIN FUEL NOZZLE WITHIN SAID CONDUIT RESTRICTED PORTION, SAID BODY HAVING AN ANNULAR SPACE AROUND THE NOZZLE OPENING INTO SAID RESTRICTED PORTION, SAID BODY HAVING A FUEL CONNECTION FROM SAID FUEL CHAMBER TO SAID MAIN FUEL NOZZLE, MEANS FOR OPERATING SAID INLET VALVE, SAID OPERATING MEANS INCLUDING A DIAPHRAGM OPERATIVELY CONNECTED TO SAID INLET VALVE AND SEALED AT ITS PERIPHERY TO SAID BODY ACROSS SAID FUEL CHAMBER TO FORM A WALL THEREOF, SPRING MEANS BIASING SAID INLET VALVE IN A VALVE CLOSING DIRECTION AND SAID DIAPHRAGM IN A DIRECTION TO ENLARGE SAID FUEL CHAMBER, MEANS FORMING A SINGLE CLOSED AIR CHAMBER ENCLOSING THE SIDE OF SADI DIAPHRAGM OPPOSITE TO SAID FUEL CHAMBER, SAID BODY INCLUDING A FIRST PASSAGE CONNECTING SAID MIXTURE CONDUIT INLET TO SAID AIR CHAMBER WHEREBY SAID DIAPHRAGM IN RESPONSIVE TO CONDUIT INLET AIR PRESSURE TO MAINTAIN FUEL IN SAID FUEL CHAMBER AT A CONSTANT PRESSURE, AND A SECOND PASSAGE IN SAID BODY INTERCONNECTING SAID ANNULAR SPACE AND SAID FIRST PASSAGE WHEREBY SAID DIAPHRAGM IN RESPONSIVE TO THE DROP IN AIR PRESSURE AT SAID CONDUIT RESTRICTIVE PORTION TO VARY THE CONSTANT PRESSURE OF FUEL IN SAID FUEL CHAMBER DIRECTLY IN RESPONSE TO CHANGES OF AIR PRESSURE AT SAID NOZZLE.