US2162056A

US2162056A - Carburetor

Info

Publication number: US2162056A
Application number: US136544A
Authority: US
Inventors: Robert F Bracke
Original assignee: Individual
Current assignee: Individual
Priority date: 1937-04-13
Filing date: 1937-04-13
Publication date: 1939-06-13
Anticipated expiration: 1956-06-13

Description

3 Sheets-Sheet 1 R.' F. BRACKE ('JARBURETOR4 Filed April 15', 1937 June l13., 1939.

June 13, 1939. RuF. BRACKE GARBURETOR Filed April 13, 1937 3 Sheets-Sheet 2 'June 13, 1939.

R. F. BRACKE cARBUREToR Filed April 13, 1937 3 Sheets-Sheet 3 BJ MIM;

Patented June 13, 1939y 9 Claims.

My invention pertains to carburetors, and is more particularly concerned with carburetors of the fuel lift type.

In non-fuel lift carburetors for automotive use, it is common to provide a main fuel supply nozzle and an idling jet. This idling jet is customarily located on the engine side of the throttle valve, and takes care of the fuel requirements of the engine during idling operation. A needle l0 valve o r other adjustable means is commonly provided to adjust this idling jet. Both the main fuel supply nozzle and the idling jet receive their fuel requirements from the float bowl of the carburetor.

Various attempts have been made to provide a fuel lift carburetory with such an idling jet. In fuel lift carburetors, however, the float bowl of the carburetor is maintained under a degree of suction sucient to draw fuel thereinto from the main fuel supply tank, usually located at the rear of the automobile. At full throttle operation the degree of suction obtaining in the carburetor float bowl is greater than that obtaining at the discharge end of the idling jet, with the result that g5 back feed of fuel and air occurs lfrom the idling jet to the float bowl of the carburetor.

disadvantageous in that it destroys the delicate balance necessary to proper operation of a fuel lift carburetor.

Y An object of my invention is to provide a fuel lift vcarburetor withx an idling jet which overcomes the foregoing disadvantages.

Another object is to provide a fuel lift carburetor with an idling jet whose supply of fuel is cut off by a throttle regulated valve under predetermined conditions.

Another object is to provide a fuel lift carburetor of the dual type, and wherein each of two idling jets is provided'with an independent adjustment. A

Another object is to provide an idling jet having a control valve mechanism which functions to enrich the mixture supplied to the engine when the throttle valve is opened.

Another object is to provide a carburetor which is simple and economical to manufacture, which will provide long and trouble-free service, and wherein the various control mechanisms may be independently adjusted.

Other objects and advantages will become apparent as the description proceeds.

In the drawings:

Figure 1 is a longitudinal section of a carburetor embodying my invention. 'I'his figure is taken on the line I-l of Figure 2.

This is:

(Cl. 26l--72) Figure 2 is an irregular horizontal section taken on the line 2--2 of Figure 1.

Figure 3 is a diagrammatic view wherein the relative positions ofthe parts are distorted but wherein their functional relationship is easier to 5 follow.

Figure 4 is a fragmentary longitudinal section similar to Figure 1, but showing a modified form of my invention. This figure is taken on the line 4-4 of Figure 5. 10

Figure 5 is a horizontal section taken on th line 5-5 of Figure 4.

I have shown my invention as being embodied in a fuel lift carburetor of the dual type. This carburetor has an air inlet I0 which may be 15 provided with any suitable air cleaner or strainer, and which supplies air to a pair of fuel feeding nozzlesl l2. Each of these nozzles discharges into a mixing chamber I4, and each mixing chamber communicates with a throttle bore I6 leading to the inlet manifold of the automobile engine.

An airvalve I8 controls the supply of 'secondary air to the mixing chambers I4. In normal operation of the engine the quantity of fuel supplied thereto is variably controlled by a pair of throttle valves 20, which are mounted on a common shaft 22 having attached to one end thereof a lever 24 provided with a ball head 26 adapted for connection to the usual hand and foot controls 'of the automobile. This lever 24 is further provided with an adjustable screw 28 which engages a stop pin 30 to determine the closed positions of the throttle valves 20.

Thetwo nozzles I2 are supplied with fuel from a common float bowl 32. This float bowl is pro- 35 vided with a threaded inlet 34 adapted to have. secured thereto a pipe leading to the main fuel supply tank at' the rear of the. automobile. Such a pipe `is indicated at 36 in Figure 3 of the drawings. The usual inlet valve 38 is provided to reg- 4() ulate the supply of fuel to the float bowl from the main fuel supply tank, this inlet valve 38 being controlled in tum by the float 40 which is pivotally supported at 42. Y

All fuel passing from the oat bowl 32 to the 45 nozzles. l2 must pass upwardly through a xed tube which is threadedly secured to the upper casting 43 of the carburetor. This tube leads to a chamber 4l which is connected with the individulil nozzlesl I2. respectively. by way of pas:- sages l! and.

Each of .the nozzles I2 has a restricted throat terminating in a step 54, and immediately below this step is a series of inclined passages 56 lead- 55 ing to an annuluar space 58. This space `communicates with one of the

passages

58 or 52.

The secondary air valve I8 may be of any suitable type. In the drawings, however, I have shown an air valve consisting of a plate 68 eccentrically mounted on a rod 62 pivotally supported in the casting 46. Attached to this rod 62are a pair of spaced weights 64, which tend to hold the plate 68 against the shoulder 66. The suction created beneath the plate 68` tends to open this valve against the resistance of the weights 64.

The movements of the airvalve |8 are dampened by dashpot mechanism comprising a cylinder 68 having' a piston 18 reciprocable therein. 'I'he piston 18 has a piston rod 12 provided with a slot 14 which receives a pin 16 extending between the two weights 64. 'Any movement of the air valve I8 thus creates a corresponding movement ofthe piston 18. In the normal operation of the carburetor the upper end of the cylinder 68 is closed to atmosphere, whereas the lower end of this cylinder is connected to the space beneath the secondary air valve I8 by means of a small opening 18 of a size comparable to that made by a No. 60 drill.

The oat bowl 32 is normally maintained under sub-atmospheric pressures by a booster 88. 'Ihis booster is in the form of a Venturi tube having a restricted throat provided withradial passages 82'communicating through an annular chamber with a duct 84 leading to the top of the float bowl 32. This booster 88 receives its air supply through a port 86 in a shiftable choke plate 88.

When the carburetor is operating under normal conditions, the plate 88 is in Ithe position shown in Figure 1 of the drawings. The pot 68 establishes communication between the inlet end of the booster 88 and the chamber 88 formed by` n through an L-shaped inlet |88.

. 'I'he booster 80 discharges into the upper end of a cylindrical space I 82 which is divided into upper and lower parts by a metal cup |84 having a-restricted orifice |86. A tapered pin |88 is located in the orice |86, and is attached to the lower end of`r the piston rod 12, whereby this 'pin shifts its vposition with the air valve I8. The function of 4this pin |88 is to regulate the flow of air through the boos r 88, and thereby maintain the desired degree of suction in the float bowl 82 under all conditions of carburetor operation.

The lower end of the tubular space |82 is in communication with a duct ||8 having `branches I I2 leading to both mixing chambers I4.

It will be understood that the chokel plate 88 is connected to the usual choke control means located on the dash of the automobile, whereby this choke plate may be shifted to facilitate starting of a cold engine. Such shifting. of the choke plate 88 restricts or entirely cuts oi the-air supply to the booster 88, thereby reducing the degree of suction obtaining in the float bowl 32 and per.-

' passage I I6 leading to the upper end of the dashpot cylinder 68. Under lthese conditions the upper surface of the piston 18 is acted upon by atmosphere, whereas the lower surface of the piston is exposed to the suction obtaining in the mixing chambers I4. This causes the piston 18 toact as an additional means for closing the secondary air valve I8.

Below each throttle valve 28 I provide an idling jet ||8. Each idling jet communicates with the lower end ofl a vertical conduit |28, and is con.

trolled by an adjustable needle valve |22.y Each needle valve may be adjusted independently of the other, and is frictionally held in adjusted position by a spring |24. The upper end of each conduit |28 communicates with 'the iioat bowl of the carburetor through means which I shall later describe.

Back bleed would occur through an. opening |25 to the noatbow1 of the carburetor if the associated idling jet |I8 were cut oi entirely by an improper adjustment of its needle valve |22.

In order to prevent such back bleed I provide each throttle bo're with an auxiliary idling jet |28. Each auxiliary idling jet |28 communicates with a conduit |28, and is of ysmaller diameter than its associated opening |26. 'I'he size of the auxiliary jets |28, however, is suiliciently large to prevent back bleed through the openings |26 l to the float bowl of the carburetor in the event that the main idling jets ||8, or either of them, is completely cut oif by an improper adjustment of its needle valve |22.

The upper end of each conduit |28 is connected with the lower end of kone of the inclined conduits |38 which lead to the opposite ends of a cross passage |32 (Fig. 2). .A metal plug having a metering orice |34 is located adjacent each end of this cross passage |32, and' meters the quantity of fuel supplied to the idlingjets ||8 and |28. The central portion of the cross passage |32 communicates with radial ports. |36 formed in a stationary sleeve |38 press-fitted or otherwise secured in the casting 46.

Inside the sleeve |38 there is a sliding tube |48 having radial openings |42 which connect the interior of the tube with the float bowl 32. 'I'he sliding tube |48 is also provided with a second series of radial passages |44l connecting the interior of the tube with longitudinal slots |46 communicating with the radial ports |36 in the sleeve |38. When the parts are in the position shown in the drawings, the idling jets I8 and |28 are capable of drawing fuel from the float bowl 32.

In order to prevent siphoning of the fuel from the oat bowl through the idling jets when the engine is not operating, I provide the upper end ofthe sliding tube |48 with a small orifice |48 which functions as an air vent to break up any i siphoning action. When the idling jets are operating to supply fuel to the engine, a small amount of air is drawn in through this opening |48 and mixes with the fuel supplied to the idling jets.

Additional air is supplied to the idling jets through the openings |26.

I shall now describe the means which I have provided for disconnecting the idling jets from the float bowl of the carburetor when the-automobile reaches Ya speed of approximately twentyfive miles per hour upon a level road and with a. normal load. T'he upper end of the sliding tube |48 threadedly engages the lower end of a cap |58 which is pivotally secured to the lower end of a link |52. 'Ihe upper end of this link is in turn pivoted to the end of an arm |54, non-rotatably secured to a shaft |56 by a pin |58.

When the throttle valves 20 are opened to a position corresponding to a car speed of twentyve miles an hour on a level road with a normal load, the sliding tube |40 is raised to such a height that the ports |42 `in the lower part of this tube are closed by the lower end of the stationary sleeve |38, and thus all communication between the idling jets and the interior of the oat bowl 32 is cut off. The speed at which this cut-off occurs cariv be varied by adjusting the screw |66. The sliding tube |40 is urged downwardly by a coil spring |10 which is interposed between the upper casting 46 and a bar |12 carried by the lower end of the tube |40. l

This bar |12 also `,carries and reciprocates a metering pin |14. 'I'his metering pin |14 has a relatively large cylindrical upper end |16 which, during idling operation of the engine, is located in a restricted opening |18 formed in the tube 44, and thereby lreduces the amount of fuel sup-A plied to the nozzles I2. This cylindrical portion of the metering pin 14 is made of appreciable length so that adjustment of the cut-off position for the idling jets does not vary the quantity of metering pin is located in the opening |18 and permits free flow of fuel to the nozzles I2.

The central position of the metering pin relativeto the orifice |18 is determined by a guide portion |84 which is located in the lower end of the tube 44. This guide portion has a passageway |86 which permits fuel to ow past the guide portion.

The bar |12 also supports and actuates the piston |88 of an accelerator pump. This piston |88 is located in a cylinder |90 which extends down into the float bowl 32 of the carburetor, and is secured to the upper casting'46 by a threaded plug |82. The piston includes a leather cup washer |94 whose lip is pressed against the cylinder wall by a coil spring |96.

The piston |88 has a hollow central portion |88 which communicates with the interior of the float chamber through passages 200 and with the interior of the cylinder |90 by wa'y of valve 202. 'I'he valve 202 is limited in its movement by a cross pin 204.

The piston |88 has a reduced stem 206 which is slidably received in an opening in the bar |12. The piston |86 is urged upwardly by a coil spring -208, the upward mvement of the piston under the influence of this .spring being limitedby a washer 2|0 secured to the lower end of the stem 206.

When the throttle valves are opened, the bar |12 is raised and the piston |88 is moved upwardly. This upward movement forces fuel from the `cylinder upwardly..through the passage at the same rate as the bar 12.

2|2 and past the check-valve 2| 4 whichis normally held against its seat by a spring 2|6 resting against a support 2|8. 'I'he fuel forced past the Valve 2|4 flows through passageways 220 to accelerating nozzles 222. Each nozzle 222 com- 5 prises a tubular piece of metal having a restricted discharge opening. i y When the throttle valves are opened slowly, the spring 208 beneath the accelerator pump piston does not compress, and this piston advances 10 However, when the throttle valves are suddenly opened through an appreciable range of movement,the resistance offered by the fuel above the accelerator pump piston |88 causes the spring 208 to compress so 15 that the accelerator pump piston does not move upwardly as fast as its actuating bar |12. After the actuating bar |12 stops its upward movement, the spring 208 expands and continues the upward movement of the piston |88. In this manner the 20 injection of the accelerating charge is prolonged beyond the opening movement of the throttle valves.

In my iriprovedcarburetor the idling jets also furnish additional fuel to the engine during an 25 opening movement of the throttle valves whichtakes place within the operating range of the idling jets, that is, before these jets have been cut oif from communication with the float chamber of the carburetor. During the normal opera- 30 tion of the idling jets, the fuel in the slots |46 of the sliding tube |40 does not rise vabove the ports |36 in the sleeve |38, and a mixture of fuel and air flows through these ports to the idling jets. When the throttle valves are opened suddenly, the 35 sliding tube l|40 is suddenly raised, and the liquid fuel in the lower ends of the slots |46 is likewise suddenly raised so that vit completely cuts off all air from the ports |36. Under the temporary condition thus created, only liquid fuel undiluted by 40 air passes through the ports |36 to the idling jets, thereby enriching the mixture supplied by these jets to the internal combustion engine.

When the engine is idling, the secondary air valve I8 is closed, and most of the air entering v4,5 the mixing chambers I4 ows through the nozzles |2. During the idling operation these nozzlesv draw little or no fuel from the oat chamber 32. Y 'I'he throttle valves 28 are practically closed, and the mixing chambers are under a pressure only 50 slightly below atmospheric.

The idling jets ||8 and |28 are located on theu engine side of the throttle valves, and are subjected to the high suction obtaining in the Yengine manifold. These idling jets draw fuel from the 55 iloat chamber ofthe carburetor. Thefuel which is withdrawn from the float chamber is mixed with a slight amount of air drawn into the vent |48 at the upper end of the sliding tube |40.

Additional air is supplied through openings |26 60 for mixture with this fuel before it is discharged through the idling jets ||8 and |28. Even during idling operation, the throttle valves 20 are not entirely closed, and a slight amount of air flows therepastfor. mixture with the fuel supplied through the idling jets. The richness of the ing chambers I4, thereby supplying additional air thereto. The throat of the booster 88 is connected by means of radial ports 82 and passage 84 with the upper end of the float chamber 32 to withdraw air and vapor therefrom.

'I'he degree of suction maintained in the float chamber by the booster 88 is regulated in part by the tapered pin |88 which varies the flow through the booster 80 and thereby varies the suction created by thisbooster. Under all ordinary conditions of engine operation the degree 'pf suction in the float bowl is suilcient to draw fuel thereinto from thel main fuel supply'tank, normally located at the rear of the automobile. During starting of a cold engine the booster 88 may be rendered entirely ineffective by shifting the choke plate 88 so that the inlet tothe booster is cut off. Such shifting of the choke plate also admits atmospheric air to the upper end of the dash-pot cylinder 88, and this air acts Iupon the piston v1I) more firmly to urge the secondary air valve I8 toward closed position. Such positioning of the choke plate, however, is used only during starting and while the engine is still cbld.

As the throttle valvesI 20 are opened to cause the engine to operate at speeds faster than idling speed, the nozzles I2 become effective to furnish greater and ever greater proportions of the fuel requirements of the engine. When the engine is operating at a speed of approximately twentyfive miles per hour on a level road and under normal 'road conditions, the nozzles I2 assume the entire burden of furnishing all of the fuel requirements of the engine. At this point the sliding tube |48 has moved upwardly to such a position that the ports |42 are closed by the lower end of the sleeve |38. thereby cutting off communications between the idling jets and the carburetor float bowl and rendering these idling jets inoperative. This same opening movement of the throttle valves raises the metering pin |14 in its associated-orifice |18 so that it offers less restriction to the ow of fuelto the nozzles I2.

. If the throttle valves are opened suddenly for the purpose of affording rapid engine acceleration, the piston |88 of the accelerator pump forces fuel into the mixing chamber through the ac-A celerating nozzles 2,22. Where the accelerating movement of the throttle valves is sudden, the spring 288 Vwhich actuates the accelerator pump piston compresses, and the pumping action of the accelerator pump piston is prolonged beyond the opening movement of the throttle valves. This q prevents choking of the engine by the too sudden supply of a large quantity of fuel through the accelerating nozzles. Upon a subsequent closing of the throttle valves, the accelerator pump piston descends in its cylinder, and during this movement the valve 282 opens to admit fuel to the cylinder |88 above the accelerating pump piston. Where a sudden opening movement of the throttle valves occurs within the range of operation ofthe idling jets, the sudden upward movement of the sliding tube |48 carries undiluted liquid fuel above the ports |36 leading to the idling jets. This temporarily provides the idling jets with additional quantities of fuel which facilitate the accelerating action of the engine.

When the throttle valves 28 are opened, the degree of suction obtaining in the mixing chamhers is increased sumciently to open the secondary alrvalve against the closing action of the weights 84. As the throttle valves 28 are opened wider, the secondary air .valve I8 also increases its opening to admit additional air therepast, When the throttle valves are fully opened, the secondary air valve I8 is also opened to its fullest extent.

When the throttle valves 28 are fullyopened, the degree of suction obtaining in the mixing chambers I4 is the same as that obtaining at the outlets to the idling jets "which are located below these throttle valves.` During Such full throttle operation the idling jets and openings |28v are exposed to a degree of suction which is less than that existing in the iloatbowl 32,/but no back bleed to the float bowl can occur because the communication between the float bowl and the openings |26 and idling jetsV II8 and |28 have been cut off by the movement of the sliding tube I 40. The point at which this cut-off occurs can be regulated by adjusting the screw-|88. Such regulation of the cut-off does not vary the operation of the accelerator pump, nor does it change f the resistance of the'economizer pin |14 to fuel ceives its supply of fuel and air from a vertical conduit |28'. This conduit has an air inlet |26 communicating with a mixing, chamber of the carburetor. The upper end of each conduit |28 is connected by a transverse port |29 with a horizontal passage |38 which connects with one end of the cross passage |32.

The central portion of passage |32 communicates with the interior of the tube |38 by way of ports |36'. The tube |88' has a larger bore |39 which. communicates with the float bowl of the carburetor by way of a smaller bore I4 I A solid rod |40' extends through the tube |88' and has its upper end attached to the cap |58. The lower end of this rod carries a bar |12. The rod |48' has a groove |43' which maintains communication between the float bowl of the'carburetor and the larger bore |38' when the automobile engine is idling or driving the automobile at speeds below 15 miles per hour and under normal load.

In this embodiment of .my invention the needle valve |22 for controlling each idling jet is so located that it controls the admission of liquid fuel to the transverse port |29. Each needle valve is maintained in adjusted position by its associated spring |24. I have found that where the needle valves/for controlling the idling jets are so arranged that they'regulate the flow of' liquid fuel only instead of a mixture of fuel and air, more stable engine operation is obtained at idling speeds.

In order to prevent siphoning of' the fuel through the idling Jets when the engine is ai rest, I provide the upperend of each conduit |28' with a very small duct l'which connects with a secondary air inlet Just below a. secondary air valve. In practice 1 have obtained excellent results where the ducts |48' are made with a No. 75 drill, the Aopenings |28 with a No. 'I0 drill. and the idling lets H8' with a No. 65 drill.

Subject matter disclosed but not claimed herein is claimed in my copending application Serial No.

' 273,853, led May 16, 1939.

fuel, a mixing chamber into which said nozzle discharges, a throttle valve 'associated with said mixing chamber, an idling jet below said throttle valve, conduit means including a valve for connecting said idling jet with said float chamber, an operating connection between said last mentioned valve and said throttle valve, an accelerating nozzle discharging into said mixing chamber, an accelerating pump connected with said accelerating nozzle, economizer means interposed between said first mentioned nozzle and said float chamber, means connecting said conduit valve with said economizer means and accelerator pump, and a booster for maintaining said float chamber under subatmospheric pressure.

2. In a fuel lift carburetorof the class described, the combination of a nozzle, a float chamber from which said nozzle is supplied with fuel, means including a metered orifice connecting said nozzle with said float chamber, an economizer pin located in said orifice, said economizer pin having a cylindrical part restricting flow of fuel to said nozzle during idling operation of an engine to winch said carburetor is attached, an idling jet, conduit means connecting said idling jet with said float chamber, a valve in said conduit means automatically operative to cut oil said idling jet from said float chamber when a predetermined condition of carburetor operation is reached, means connecting said economizer pin with said valve for movement therewith, means for adjusting said valve without disturbing the restrictive function of said economizer pin during idling operation ofthe engine, means for operating said valve and economizer pin, and a `booster for maintaining said float chamber under sub-atmosv pheric pressure.

3. Ina fuel lift carburetor of the class described, the combination of a float bowl adapted to hold a quantity of fuel, means for maintaining said float bowl under sub-atmospheric pressure,

a main nozzle supplied with fuel from said float bowl, a conduit connecting said nozzle with said, float bowl, said nozzle being capable of drawing fuel from saidA float bowl under all conditions of carburetor operation, an idling jet supplied with fueljfrom said float bowl, a second conduit connecting said idling jet with said float bowl, the absolute pressure in said idling jet Vbeing greater under, certain conditions of carburetor operation than the absolute pressure in said oat bowl whereby under said conditions of carburetor operation back bleed into said float bowl through said second conduit would normally occur. valve means controlling communication between said ioat bowl and idling jet, and automatic means operable upon creation of a pre-determined con' dition of carburetor operation to closel said valve and prevent back bleed Ainto said float bowl.

4. In a fuel lift carburetor of thel class de scribed, the combination of a float bowl adapted to hold a quantity of fuel, means for maintaining fuel from said float bowl under all conditions of carburetor operation, an idling jet Supplied with fuel from-said float bowl, a second conduit connecting. said idling jet with said float bowl, the absolute pressure in said idling jet being greater under certain conditions of carburetor operation than thel absolute pressure in .said float bowl whereby under said conditions of carburetor operation back bleed into said float bowl through said second conduit would normally occur, valve means controlling communication between said quantity of fuel, means for maintaining said float bowl under sub-atmospheric pressure, 4a. main nozzle supplied with fuel from said float bowl, a conduit connecting said nozzle with said float bowl, said nozzle being capable of drawing fuel from said float bowl under all conditions of carburetor operation, an idling jet supplied with fuel: from said float bowl, a second conduit connecting said idling jet with said float bowl, said second conduit having an air inlet, the absolute pressure in said idling jet being greater under certain conditions of carburetor operation than the absolute pressure in said oat bowl whereby under said conditions of carburetor operation back bleed into said float' bowl through said second conduit would normally occur, valve means in said second conduit to prevent back bleed therethrough, said valve means being located between said oat bowl and said air inlet, a throttle valve controlling communication between said main nozzle and an internal combustion engine -to which said carburetor-is attached, and a connection between said throttle valve and said firstmentioned valve to close the latter when said throttle valve is opened a predetermined amount.

6. In a fuel lift carburetor of the class described, the combination of a oat bowl adapted to hold a quantity of fuel, ,means for maintaining said float bowl under sub-atmospheric pressure, a main nozzle supplied with fuel from said float bowl, a conduit connecting said nozzle with said float bowl, said nozzle being capable of drawing fuel from said oat bowl under all conditions of carburetor operation, an idling jet supplied with fuel from said iloat bowl, a second conduit connecting said idling jet with said float bowl, the absolute pressure in said idling jet being greater under certain conditions of carburetor operation than the absolute pressure in said float bowl whereby under said conditions of carburetor operation back bleed into said float bowl through said second conduit would normally occur, valve means for closing said second conduit to prevent back bleed therethrough, said second conduit having a portion located above said valve, a throttle valve controlling communication between `said main nozzle and an internal combustion engine to which said carburetor is attached, and a connection between said throttle valve and said mst-mentioned .valve to close the latter when said throttle valve is opened a predetermined amount.

7. In a fuel lift carburetor of the class described; the combination of a float bowl adapted the combination of a float bowl adapted to hold a to hold a quantity of fuel, means for maintaining said float bowl under sub-atmospheric pressure, a main nozzle supplied with fuel from said float bowl, a conduit connecting said nozzle with said iloat bowl, said nozzle being capable of drawing fuel from said float bowl under `all conditions through, a throttle valve controlling communication between said main nozzle and an internal combustion engine to which said carburetor is attached, and a connection between said throttle valve and said first-mentioned valve to close the latter when said throttle valve is opened a predetermined amount.

.8. In a fuel lift carburetor of the class described, the combination of a oat bowl adapted to hold a quantity of fuel, means for maintaining said float bowl under sub-atmospheric pressure, a main nozzle supplied with fuel from said iioat bowl, a conduit connecting `said nozzle with said float bowl, said nozzle being capable of drawing fuel from said float bowl under all conditions of carburetor operation, an idling jet' supplied with fuel from said float bowl, a second conduit con necting'. said .idling jet with said float bowl, said second conduit having a portion located above the fuel in said float bowl, the absolute pressure in ,said idling jet being greater under certain conditions of carburetor operation than the absolute pressure in said float bowl whereby under said conditions of carburetoroperation backbleed into said float bowl through said second conduit would normally occur, valve means in said float bowl for closing said second conduit to prevent back bleed therethrough, said valve means being submerged in the fuel in said float bowl, a throttle valve controlling communication between said main nozzle 4and an internal Acombustion engine to which said carburetor is attached, and a connection between said throttle valve and said first-mentioned valve to' close the latter when said throttle valve is opened a predeterminedamount.'

9. In a fuel lift carburetor of the class de-4 scribed, the combination of a float bowl adapted to hold a quantity of fuel, means for maintaining said float bowl under sub-atmospheric pressure, a main nozzle supplied with fuel from said float bowl, a conduit connecting said nozzle with said float bowl, said nozzle being capab1e of drawing fuel from said float bowl under all conditionsvof carburetor operation, an idling -jet supplied with fueifrom said float bowl, a second conduit connecting said idling jet with said float bowl, the absolute pressure in said idling jet being greater under certain conditions of carburetor operation than the absolute pressure in said float bowl whereby under said conditions of carburetor op- ROBERT BRACKE.

- eration back bleed into said float bowl through