US2315717A - Carburetor - Google Patents

Description

April 6, 1943. w. E. LEIBING- ETAL CARBURETOR Filed May 1, 1941 3 Sheets-Sheet l m m Z W Wm W M ,0 m WR mm 0, i M 6% w. 0v m 2 WW mm m m6 mm 8 ad A ril 6, 1943.. w. E. LEIBING ETAL 2,315,717

. CARBURE'IOR 4 Filed May 1, 1941 '3 Sheets-Sheet 2 n we n ow 4 1mm, flawalaiww M2 du-ouw April w. E. LEIBING ETAL 2,315,717

GARBURETOR Filed May 1, 1941 3 Sheets-Sheet 3 kallgfl. 159ml Patented Apr. 6, 1943 UNITED STATES PATENT OFFICE CAR-BURETOR William E. Leibing, San Rafael, Calif., and Robley D. Fageol, Grosse Pointe Farms, Mich, assignors to Leibing-Fageol Company, Detroit, Mich.,

a partnership composed of F.

R. Fageol,

Application May 1, 1941, Serial No. 391,412

Claims.

The present invention relates to improvements in carburetors for internal combustion engines, and more particularly to that class of carburetors in which the throttle valve for controlling the flows through the fuel conduit is positioned on the atmospheric side, or up-stream side, of the jet, or jets, feeding the fuel into the conduit, such a carburetor being sometimes known as the anterior throttle type. However, it is to be understood that a number of the features disclosed herein are applicable as well to carburetors of any type.

The present invention is intended as an improvement over the carburetor disclosed in application Serial No. 359,282, filed October 1, 1940, having as a major object the provision of a metering means of novel construction for'supplying fuel to a single jet in the carburetor for normal running conditions of the engine, includ ing idling, thus eliminating the necessity for a special idling jet with its attendant fuel supply and adjustment means.

A further object of my invention is the provision of a novel fuel metering means for a carburetor wherein a fuel metering arm within a fuel chamber is provided to move in accordance with the throttle valve shaft, the connection of the arm and the shaft being protected against the access of fuel thereto under normal running conditions with consequent leakage of excess fuel into the carburetor conduit.

A further object of the present invention is to provide novel fuel metering means wherein the size of the fuel metering opening, or openings, can be readily varied to adapt the metering means to different engines and different conditions of operation at different throttle positions without expensive machinery or material alteration of any parts.

Still a further object of this invention is the provision of a carburetor having novel metering means adapted to be variably immersed in the fuel in the float chamber of the carburetor, means being provided to eliminate the effect of variations in the fuel level in said chamber and provide ready means to vary the air fuel ratio developed by the metering means.

A further object of the invention is the provision of a carburetor having novel fuel metering means wherein the effect of tips, angles, and surge within the float chamber are eliminated to an extent whereby the carburetor is capable of satisfactory use on cross-country vehicles such as tanks, tractors, trucks, reconnaissance cars, and like military vehicles.

Still a further object of the invention is the provision of a novel carburetor wherein by the substitution of throttles of different angularitles when in closed position, considerable change in throttle progression can be effected, means being also provided in the substitution of relatively simple and inexpensive elements to change the air fuel ratio relative to various positions of the carburetor throttle.

A further object of the invention is the provision of a novel method of varying the character of the fuel mixture developed by a carburetor which includes the step of correlating the angularity of the throttle valve to the fuel metering means to predetermine the rate of effective opening through the carburetor conduit corresponding to the movement of the metering means by the throttle valve.

A further object of the invention is to provide a novel method of varying the fuel mixture developed by a carburetor having slotted metering means arranged to be progressively immersed in liquid fuel which comprises the step of sealing the slot in the metering means from the liquid fuel at the fuel level line and varying the length of said sealing means to vary the length of the metering slot sealed by the sealing means.

Still a further object of the invention is the provision of a novel method of varying the fuel mixture developed by a carburetor having slotted metering means arranged to be progressively immersed into liquid fuel by varying the effective opening of said slot at points corresponding to predetermined positions of the throttle valve.

Other objects and advantages of the present invention will appear from the following description and claims, including the appended drawings, wherein Figure 1 is a side elevation, partly in section, of a preferred embodiment of the present invention in a carburetor of the anterior throttle down-draft type taken on the line i-l of Fig ure 4.

Figure 2 is a section taken on the line 2-2 of Figure 4, looking in the direction of the arrows.

Figure 3 is a section taken on the line 3-3 of Figure 1.

Figure 4 is a plan of the carburetor as it appears in Figure 3.

Figure 5 is a side elevation looking from the right of Figure 4, with certain control connections added.

Figure 6 is a longitudinal section on an enlarged scale of the metering arm of Figure l.

Figure 7 is a section taken on the line l-l of Figure 6, with a portion of the throttle valve shaft added.

Figure 8 is a perspective of the assembly shown at the upper lefthand corner of Figure 1.

Figure 9 is a section taken through the gasket of the metering arm of Figure l with a modified type of adjustment and control means shown in combination therewith.

Figure 10 is an elevation of the adjustment block of Figure 9 as reviewed from the right of that figure.

Figure 11 is a plan view of the adjustment block and a portion of the metering arm viewed in the direction of the arrow in Figure 9.

The present invention is described for the purpose of illustration in connection with a carburetor of the down-draft type, the arrow in Figure 2 indicating the direction of the flow of fluid through the carburetor. In all the figures, corresponding numbers are employed to indicate like parts.

Referring to Figure 2, A generally designates a carburetor having a fuel mixture section B and a choke section C, the latter being of conventional construction. Section B includes a conduit section I! defining a passageway or fuel conduit [2, section B being provided at its lower end with a flange 13 having lug [4 (Figure 3) thereon with suitable apertures for fastening to an intake manifold (not shown) of an internal combustion engine in customary manner.

Conduit H is fitted at its discharge or lower end with a venturi l5 of conventional type, a fuel jet or nozzle l6 being mounted in the conduit wall at H with its slightly flared discharge end It positioned in the throat of venturi l5 and its inlet end connecting with a passage l9 formed in the wall of the carburetor.

Above jet [6, the conduit walls are apertured as at 2| to receive a throttle shaft 22 mounting a throttle valve 23, preferably of the butterfly type. Above throttle valve 23 in choke section C is a choke valve 24 of conventional type arranged to be operated in well known manner by conventional controls (shown in Fig. 5) such as a Bowden wire 25 mounted on a bracket 26 and connected to a crank arm 21 on the choke valve shaft. An air cleaner of conventional type (not shown) is provided above choke section C so that the air entering the carburetor will be relatively free of dust and like impurities.

As viewed in Figure 2, throttle valve shaft 22 extends to the right and connects with wellknown control means 28 (Figure 5) having an idling adjustment assembly 29 associated therewith. At its left end (Figures 1 and 2), shaft 22 extends into a float chamber 3|, preferably formed integral with conduit section B. Float chamber 3| includes a lower section 32 serving as a fuel reservoir and a cover section 33, the latter being reduced at its top as at 34 (Figure 2) and merging into a conduit 35 leading into choke section C above choke valve 24. This insures that the only air accessible to the top of the float chamber 3| must first pass through the air cleaner and be cleaned thereby.

As shown in Figure 1, float chamber 3| has a connection 36 for a fuel supply conduit (not shown) leading from a suitable source of fuel, a connecting nipple 31 being formed with a valve seat 38 and a valve guide 39 to receive a needle valve 4| arranged to operate in a horizontal plane and control the entrance of fuel into the float chamber.

Needle valve 4| is preferably square or triangular in cross-section, as shown, to offer a minimum of resistance to the passage of fuel. An arm 42 is pivoted for oscillation in float chamber 3! about a shaft 4.3, arm :2 being provided with an extension 44 positioned to engage the head of needle valve 4!. A pair of floats 45 and 46 are secured to the opposite end of arm 42, the arm at this end being formed as a yoke with two extending portions 41 and d8, each of which is secured to a float. As shown in Figure 3, floats 45 and 46 are disposed symmetrically at opposite sides of the float chamber, and are spaced from the center thereof whereby they tend to maintain the fuel level constant despite the various angled positions assumed by the carburetor incident to its use on a motor vehicle. Floats l5 and 4B are connected together at their outer ends by a brace member all.

By reason of a horizontal partition 49 and a vertical partition 5! in the float chamber, the needle valve assembly is contained in a chamber that is entirely filled with fuel at all times, this following because of the fuel level maintained on a line FL of Figure 1. This arrangement is unlike prior arrangements where it has been the practice to place the needle valve and the chambar in which it operate in a vertical plane. Such prior devices have become filled partly with air and partly with fuel. As a result, any surge of the fuel in the direction of the needle valve chamber permits the fuel to wash out from under the floats Which fall and permit excess fuel to enter, while a surge in the opposite direction or away from the needle valve chamber permits the fuel to again influence the floats. The resultant operation is highly unsatisfactory, particularly when such carburetors are used on vehicles constantly being displaced angularly, such as tractors and tanks.

In the construction herein disclosed wherein the needle valve chamber is always sealed with liquid fuel, surge will not cause more fuel to enter, and under either normal or angular operation, no fuel can flow out (and be replaced by air). Therefore, the floats 55 and 46 are the sole controlling factors as to change of levels when the float chamber is tipped and as the floats are concentric of the area of the float chamber, they function to maintain a constant level at the center of the area regardless of the angle of the chamber. As the metering arm (as will be hereinafter explained) is at the central point or center of concentricity of the float chamber where the level is constant, it follows that the fuel head effective on the metering arm will be substantially constant. As all the fuel for all positions of operation is supplied by the metering arm, the carburetor will function correctly at any angle up to the point where the fuel will flow b gravity over the upper edge of vertical partition 55, or the floats refuse to control the flow. The embodiment shown in Figure 1 will function correctly up to and including 60 percent grades.

Referring to Figure 2, throttle shaft 22 is provided with a cross bore or passage 52 connecting with passage IS in all operating positions of the shaft, and with a bore or passage 53 opening into the outer periphery of the shaft at 5 A metering arm '55 is fixed, to throttle valve shaft 22 at its left end in such a position that when the throttle is in fully closed position, arm 55 willbe in the position shown in Figure 1, and be held in such position by screw 56 entering the end of shaft 22, and washer 57, which seals the end of the shaft 22. To permit ready access to screw 56 and the end of shaft 22, the float chamber is preferably bored and tapped at 58 and fitted with a screw plug 59.

Arm 55, shown in enlarged size in Figures 6 and '7, constitutes the metering means and is preferably made in two complemental halves 6| and 62 arranged to be firmly fastened together by screws 63 or like fastening means and held in matched position by dowels 64 and 65. An S-shaped conduit or groove 66 of semi-circular cross-section is cast or otherwise formed in each arm section (right and left shaped), so that when halves and 62 are assembled, a passage, substantially circular in cross-section, beginning at 61 and continuing in an S-shape is formed. The outlet end 68 of thi passage terminates with and aligns with passage 54 in throttle valve shaft 22 (Figures 2 and '7).

Before assembling section halves SI and 52, a gasket 69 of fiber or similar material having the same general outline as arm 55 with all the holes therein required for assembly and of any desired thickness is placed between the halves BI and 62. As will be noted in Figures 1 and 6, a portion of gasket 69 corresponding to the outer periphery of arm 55 is cut away, the cut-away section being represented by dotted line ll, 12. and 13 in Figure 6. With such gasket 69 in place between the arm sections, and the sections firmly secured together, a portion of the S- shaped passage formed in the arm 55 is in communication with the atmosphere above the fuel level in the float chamber by a slot 14 (Figures 1, 2, and 7), this slot being of a width corresponding to the thickness of gasket 69. By varying the thickness of gasket 59, the Width of slot 14 can be readily varied. This provides an easy and cheap means of adjustment which does not require any extensive machining or mutilation of the parts so that they cannot be returned to their original adjustment.

The length of that portion of the S-shaped passage in the arm exposed to atmosphere (in the position shown in Figure 1) is represented by the area between lines 1! and 73, where the gasket has been cut away. Obviously the length of this slot can be easily varied by varying the extent to which the gasket is cut away, i. e., the positions of lines H and 13.

While the S-shaped hole formed between the section halves SI and 62 will be circular in crosssection between lines H and 13, it is formed as two half-circular holes, one-half on each side of gasket 69, after passing line 13, as shown at 15 and 16 (Figure '7) and such half holes continue until connection is made with the throttle shaft passage 54.

The metering arm 55, above described, is possessed of a number of advantages in its operation in that its shape with respect to its entry into the liquid fuel prevents over correction at closed, or nearly closed, positions of the throttle, while in the other positions, it operates to automatically correct the mixture to insure the feed of the correct air fuel ratios to the carburetor conduit.

As shown in Figure 1, vertical partition 5| extends upwardly to a point where it terminates adjacent the curved underside of arm 55. The upper part of the partition therefore acts as a fence or seal in combination with the inside curve of arm 55 to prevent fuel from the float chamber reaching a point adjacent the throttle valve shaft and the connection of arm 55 thereto,

whereby the possibility of liquid fuel being drawn in'to'the carburetor conduit around the bearing and connections to the throttle valve shaft and upsetting the mixture is eliminated.

To further insure correct operation of metering arm 55 and to further protect against the ill effects of changes in the fuel level in the float chamber, indicated in Figure 1 by dotted line FL, a fiber or Bakelite block 11 having a curved inner face 18 of channel shape and of the same curvature as the slotted periphery of arm 55 is arranged to be resiliently held against the slotted face of arm 55 and rigidly held in vertically adjustable position as shown in Figure 1. In the position therein shown, where arm 55 is in a position corresponding to idling or closed throttle position, a small portion of the slot in arm 55 is below block '17 in the liquid fuel, while the balance of the slot above block H is open to air. As block 1! is positioned so that fuel level line FL passes substantially through the center thereof, it is obvious that the fuel level may rise and fall to a considerable extent without altering the portions of slot 14 that are exposed to fuel and air and without changing the air-fuel ratio at the position shown.

In this idling position, it will be noted that the lower loop of the S-shaped passage 66 is above fuel level line FL. This is important under some conditions. For instance, in re-starting a warm engine, if the loop be below fuel level line FL, the air will be valved off entirely. This would cause the engine, while being cranked, to go too rich at the idling position where the air-fuel ratio is always touchy, so that the engine would refuse to start. With the arrangement herein disclosed, this valving off of fuel can be delayed to any desired throttle position when the engine is not as touchy as at idling, the control being the position of the lower loop of passage 66 as regards fuel level at the idling position.

With reference to Figure 1, it is apparent that upon opening the throttle from closed to open position, arm 55 will rotate in a counter-clockwise direction and be progressively immersed in the liquid fuel. Such movement will immediately increase the proportion of the slot below block 11, and therefore increase the amount of fuel fed by the arm 55. At the same time, such movement will decrease the proportion of the slot above block 1'! and proportionately diminish the amount of air admitted to the passage in the arm. Both operations tend to enrich the amount of fuel in direct proportion to the degree of opening of the throttle.

It is also to be noted that if a degree throttle valve be used, i. e., a throttle valve which when closed is diametrically positioned across the carburetor conduit, arm 55 would move relatively rapidly in going from a position corresponding to closed throttle position to a position corresponding to open throttle position as regards the amount of space made available for the passage of air through carburetor conduit I2 by such a 90 degree throttle. If a 70 degree throttle be used (a throttle valve which is 20 degrees away from a diameter when in closed position), the same relative movement of arm 55 would open a considerably greater space for the passage of air through carburetor conduit I2. From this observation, it is apparentthat with no other change than the angle of the throttle in closed position, any desired change in throttle progression can be made.

When the thottle valve is in fully open posi tion, slot M will be entirely beneath fuel level line FL. At heavy loads and low engine speeds, the fuel would tend to syphon from the float chamber to the fuel jet which flow might be greatly in excess of engine requirements. Or if the engine be shut off in wide open throttle position, the liquid fuel would also continue to flow by syphon action even though the engine is not running. To prevent such occurrences, a jet i9 is placed in the s-shaped passage (Figures 1 and 6) at a point where it can function to prevent such a syphon action and also perform as a mixture control jet, as will be later described. It has also been found desirable to place an auxiliary air jet 8! in the extreme end of the S- shaped passage 66 in arm 55 (Figures 1 and 6) where it will always be above fuel level line FL even though the throttle be in wide open position.

It has been found possible without changing the width of slot 14 in arm 55 to vary the airfuel ratio by a trade of values between jets "I9 and ti. For instance, with a slot 14 having a width of 0.010 inch and an anti-Syphon jet 19 having a diameter of 0.022 inch, the mixture at wide open throttle and below 30 miles per hour can be enriched by substituting an 0.020 inch diameter anti-syphon jet 19. At speeds above 30 miles per hour, it has been possible to vary the mixture without disturbing the slot width by changing the diameter of jet 3!. The latter change will not influence the change in antisyphon jet Z9 and the change in the anti-syphon jet will but little influence the latter.

On some engines, it has been found that the fuel requirements in going from one throttle position to another are not uniform and some modification of the straight or uniformly wide slot I is required. This problem is readily solved by milling a cut of any desired width or depth on the inside face of one or both of the arm halves iii and 62. Or an extra cut in the gasket 69 may be made in advance of dotted line 't'i (Fig. 6) which extra cut acts as a power jet when the corresponding position of the throttle is reached and gives the added fuel necessary for the added power which the throttle position indicates is required.

A further control of the air fuel ratios delivered by metering arm 55 in operation is found in the length of block 'i'! which is illustrated in Figure l as of minimum length. For instance, by increasing the length of block Ti above fuel ievel line FL, the air entering slot 14 in arm 55 is metered off that much sooner while leaving the total liquid fuel flow area below the block as before.

The above described assembly sets up three stages of control as regards throttle progression.

The first resides in the angle of the throttle selected in the closed position which controls the rate of opening of the available air flow passage in the carburetor conduit as the throttle is opened. This fuel control covers a range up to approximately 1,000 R. P. M. light load.

The second control resides in the selection of the length of block 11 which controls the fuel flow in relation to throttle movement up to approximately 2,500 R. P. M. light load.

The third control resides in the thickness of gasket 69 which determines the width of slot 14. While a change in slot width is naturally refiected in all stages of control, it is most important in the final stage, or between 2,500 R. P. M. and wide open position.

The three aforementioned controls plus the anti-syplion jet 79 and the air bleed 5i establish a control for the entire range of throttle progression and for any variation in loads or R. P. M. of the engine at any throttle position.

Still a further control is available in the ability to make slot 14 of non-uniform width and to correlate the portions of different width with corresponding throttle positions.

It is important that block 11 be mounted in a manner whereby no wear can develop that would tend to permit it to oscillate in a vertical plane. In the present invention, this is accomplished by providing a tapered metallic button 82 integral with block H. A. spring wire member 83 with a loop at both ends is provided, the upper loop of member 83 being fulcrumed about a pin 84 in a manner whereby spring member 83 can swing sideways to allow for variations in the position of float chamber cover 33, and other manufacturing errors, while the lower loop fits over tapered button 82 on block Ti. As shown in Figure 1, member 83 functions to firmly urge block 71 to the right against the periphery of arm 55. If wear develops between the lower loop on member 83 and button 82. the loop merely moves to the right on the tapered portion of the button. In this manner, the loop can be depended upon to hold the block in its selected position at all times.

Pin 84 and the upper loop of spring member 83 are contained within a hollow boss 85 formed in cover 3| of the float chamber, the inner bore 86 of boss 85 at its upper end being square or noncircular in cross-section to receive a tubular-like member 87 of corresponding cross-sectional shape. Such shaping permits longitudinal movement of member 87 in the hollow boss, but prevents rotation. A stud 88 is fixed to the upper end of member 87. A nut 89 is threaded to stud 88- whereby on rotation of nut 89, member 81 can be vertically adjusted to effect a like adjustment of block 71. Serrations 9! on the upper surface of the boss and the lower face of the nut prevent the nut from vibrating from its adjusted position.

A compression spring 52 is provided in member Bl in combination with a plug 93 to keep the upper loop of spring member 83 firmly down against its fulcrum pivot 84 and prevent any vertical movement thereof.

The lower part of boss 85 is enlarged to receive a relatively heavy compression spring 94 which reacts against flange 95 on member 81 and shoulder 95 inside the hollow boss to strongly urge the entire spring supporting assembly downward.

As shown in Figure 1, fuel level line FL passes through the center of button 82 on block Ti and in the relation shown, the fuel level may rise or fall as much as without any appreciable effect on the air fuel ratio developed by arm 55. In Figure 1, only a small portion of slot M is exposed to fuel below block ll. In this position, which is the closed throttle or idling position, if an adjustment of the fuel ratios is required, block Ti may be raised by turning nut 89 to expose more of slot 74 to the fuel to enrich the mixture. If it is desired to lean the mixture, block ll may be lowered, and the amount of slot M exposed to liquid level be shortened.

To provide for injecting fuel into the carburetor conduit when rapid acceleration is desired, a pump cylinder 91 is formed in the bottom of float chamber 3!, cylinder 91 having an apertured piston 58 therein carrying a check valve 99 of conventional type whereby fuel is free to pass down throughthe piston but=n t upwardly.

Referring to Figures 1 and 3,, a connecting link IOI formed of spring wire isattached to metering arm 55 by a pin or screw I02 and do the top of piston 98 by a pin or screw I03. Upon sudden opening movement of j the carburetor throttle, the link IOI is distorted and loaded. In returning to its original shape, it forces piston 95 downwardly to pump a sustained charge of fuel out of cylinder 91 through a discharge port I04 connected by a conduit (not shown) to a boss I05 (Figure 5), and a discharge jet I06 (Figures 2 and 5). In this connection, check valves (not shown) are used as in conventional practice.

In Figure 5, a boss I! is shown provided with a tapped bore I08 and an aperture I09 drilled just above throttle valve 23 when the latter is in closed or idling position to provide the desired spark control connection which functions in well known manner.

Figures 9, l0, and 11 illustrate a modified form of block and adjustment means for the metering arm 55 which provides a less sensitive idling mixture and adjustment means than hitherto described, and is particularly adapted for providing cheap and accurate means for controlling airfuel ratios at throttle positions just above idling position and for as long or as short a period in the opening phase of the throttle as different makes of engines may require. Different makes of engines have different requirements just above idling position, which requirements extend over different periods for each type of engine. This has been a difficult problem in the automobile industry and attempts have been made in the past to solve it by some devices as idling jets having openings of peculiar shapes and idling jets provided in combination with so-called second holes having adjustable means in combination therewith.

In solving this particular problem in a cheap and reliable manner, a metering arm 55 of the same construction as hitherto described is used, except that gasket 69 is provided with an angular cut H4 which it is understood may be varied in both angle and position for different types of engines. This metering arm is employed in combination with an adjustable block 11' (Figs. 9, l0, and 11). Block 11 difiers from block T! of Fig. 1 in that it is formed with two grooves III and H2 separated by a solid portion or neck H3 extending into contact with the curved edge of metering arm 55. The portion of block 11' above neck H3, in which groove III is formed, extends sufficiently far above the fuel level line so that fuel will not be surged and splashed into it while the portion of block TI in which groove H2 is formed extends sufiiciently far below the fuel level line to insure against any surge or splashing of the fuel uncovering the groove.

The lower end of groove I I I terminates just below fuel level. line at neck I I3 which acts as a seal between groove III and groove H2, neck H3 being of predetermined length, as determined by the characteristics of the engine upon which the carburetor is to be used.

A hole H is formed in neck H3 connecting with the slot in the edge of the metering arm, as shown in Fig. 9, a second hole I It, metered, being drilled between the lower end of groove III and hole H5.

In operation with the engine running, groove I I2 is always full of liquid fuel, and according to the adjustment made at idling position (the position shown in Fig. 9), a small portion of the slot in the edge of metering arm 55, determined by th thickness of gasket 69 and the angle of cut H4, is exposed to liquid fuel. At the same time hole I I5 straddles or caps the slot in the metering arm at a point above the point of access of the liquid fuel and between the liquid fuel and the low pressure area in the metering slot. By metering hole H6, which connects hole II5 to atmosphere, any desired pressure can be maintained in the metering slot at the point immediately adjacent hole I I5. This arrangement eliminates the necessity of using any small openings coupled with relatively large pressure differentials, which openings are difl'icult to maintain in service, and enables any desired amount of the slot provided by cut-away portion I of gasket 69 to be exposed to groove II2, while eliminating all sensitiveness in the adjustment of the fuel fed in the idling or closed throttle position.

As the metering arm rotates counter-clockwise (as viewed in Fig. 9) corresponding to opening movement of the throttle, a greater length and depth of the metering slot is exposed to groove II2 as well as to a greater depth of fuel.

Difierent makes or types of engines have substantially different fuel requirements, particularly between idling R. P. M. and 1000-4200 R. P. M. In the present invention, these requirements are easily and cheaply met by varying the angle and extent of cut of gasket 69 at t, the shape and length of the out being capable of any variation. All the undesirable sensitivity incident to conventional idling adjustments is eliminated by the admission of air through holes H5 and lit, the throttle progression (which at this phase of operation really means the air fuel ratio at the touchy point just off idling) is controlled by no more eX- pensive means than a cut of predetermined shape in a gasket made of fiber, or like material.

It is to be understood that the invention may be embodied in specific forms other than that illustrated without departing from the principle or essential characteristics thereof. The embodiments shown are therefore to be considered as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description and drawings. All modifications and changes which come within the meaning and range of equivalency of the claims are therefore intended to be included therein.

We claim:

1. A carburetor for an internal combustion engine comprising a conduit, a throttle valve in said conduit, a float chamber, a fuel jet in said conduit, and means to conduct and meter fuel to said fuel jet from said float chamber comprising a slotted member arranged to be progressively immersed in the fuel in said float chamber as said throttle valve moves from closed to open position,

means to seal the portion of said slot immediately adjacent the fuel level line in said float chamber in all positions of said slotted member, and means to control the pressure in said slot adjacent aid fuel level line.

2. The combination claimed in claim 1 wherein duit, and means to 'cond'uctand meter iuel to said fuel jet from "said float chambercomprising a slotted member 1 arranged to be progressively immersed in the fnel'in said float-chamber as said throttle valve moves from closed to open position, and meansto seal the portion-ofsaid slot immediately adjacent the "zfuel level line in said 'float chamber comprising a. block having a groove therein substantially parallel to said slot, and means in said groove in sealing relation with-said slot to divide said groove into a section below the fuel level line-and a section extending above vthe fuel level line to the atmosphere in said float chamber.

4. The combination claimed in claim 3 wherein said sealing means is connected to said upper groove through a metered aperture.

5. Aearburetor"ior-an intemal combustion engine-comprising a conduit, a throttle valve in said 'conduiwa fioat chamber, aiuel jetin said conduit, andmeans to'conduc't and meter fuelto said "fuel

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