US3904712A

US3904712A - Carburetor fuel bowl vent

Info

Publication number: US3904712A
Application number: US436492A
Authority: US
Inventors: Roland S Taylor
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1974-01-25
Filing date: 1974-01-25
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09
Also published as: JPS5342659Y2; JPS5127729U

Abstract

A light metal fuel bowl vent valve disc is pressure responsive to allow automatic venting of the bowl. A resilient arm is attached at one end to the fuel bowl cover and is curled at the other end to engage and open the valve disc. The arm is moved by a radially extending flange attached to the top of an accelerator pump stem or spring retainer. The arm is adjustable relative to the flange to open the valve only when the pump is near its uppermost position. In one embodiment the arm carries and is moved by an adjustment screw which engages the flange, whereas in a second embodiment the arm has lower and upper portions which are spread by an adjustment screw and a tang extending from the upper portion of the arm engages the flange.

Description

United States Patent [1 1 Taylor [4 1 Sept. 9, 1975 CARBURETOR FUEL BOWL VENT Roland S. Taylor, Fairport, NY.

General Motors Corporation, Detroit, Mich.

[22] Filed: Jan. 25, 1974 [21] Appl. No.: 436,492

[75] Inventor:

[73] Assignee:

[52] U.S. Cl 261/34 A; 261/72 R; 261/DIG. 67

[51] Int. Cl. F02m 5/08 [58] Field of Search 261/34 A, 72 R, DIG. 67

[56] References Cited UNITED STATES PATENTS 2,741,465 4/1956 Redman et a1 26l/DIG. 67 2,867,423 1/1959 Wing 261/DIG. 67 3,001,774 9/1961 Sarto t .1 261/42 3,110,749 11/1963 Marsee 261/34 A Primary Examiner Tim R. Miles Attorney, Agent, or FirmC. K. Veenstra 57 ABSTRACT A light metal fuel bowl vent valve disc is pressure responsive to allow automatic venting of the bowl. A re silient arm is attached at one end to the fuel bowl cover and is curled at the other end to engage and open the valve disc. The arm is moved by a radially I extending flange attached to the top of an accelerator pump stem or spring retainer. The arm is adjustable relative to the flange to open the valve only when the pump is near its uppermost position. In one embodiment the arm carries and is moved by an adjustment screw which engages the flange, whereas in a second embodiment the arm has lower and upper portions which are spread by an adjustment screw and a tang extending from the upper portion of the arm engages the flange.

3 Claims, 4 Drawing Figures PATENTED SEP 91975 saw 2 0f 2 CARBURETOR FUEL BOWL VENT This invention relates to carburetors for internal combustion engines and, more paticularly, to carburetors having means which vent the carburetor fuel bowl when the accelerator pump is near its uppermost position.

In the operation of carburetors, it is desirable to vent the fuel bowl if an excess amount of fuel vapor is produced by the fuel therein, as when the engine is hot and the throttle is closed. This might occur during idling, deceleration, or immediately after the engine is stopped, i.e. a hot soak. The accumulation of vapor in the top of the fuel bowl can be minimized by venting the top of the fuel bowl to the atmosphere or to a vapor collection canister for subsequent return to the carburetor.

Means for venting carburetor fuel bowls during closed throttle operation have been provided in the past. For example, in U.S. Pat. No. 2,867,423 Wing a carburetor bowl vent valve is described which is operated by the throttle and opens when the throttle valve is closed. Also, spring biased rubber vent valves coacting with the accelerator pump linkage have been used for closed throttle venting, as have light metal valve discs for automatic, self-venting. Some vent valves have been opened by linkage extending from the carburetor accelerator pump, which is a desirable feature since the accelerator pump is normally in an uppermost position during closed throttle operation of the engine.

It is the principal object of the present invention to provide means for operating a carburetor fuel bowl vent valve comprising a resilient actuating arm engaged by a radially extending flange attached to the accelerator pump stem, and effective to open the valve only when the accelerator pump is near its uppermost position which occurs when the throttle is closed. In a preferred embodiment, the environment surrounding the present invention includes a fuel vapor region in the top of the carburetor fuel bowl has a passage extending from an aperture in the top of this bowl to a vapor collection canister to obtain a vapor venting system which minimizes vapor loss to the atmosphere. The valve is essentially a round plate of light metal which sealingly seats in the aperture to prevent vapor discharge from the bowl when the bowl vapor pressure is insufficient to unseat the disc, but will allow the bowl to vent if such pressure is excessive.

There are two illustrated embodiments of the operating arm but both have several features in common: one end of the arm is secured to the top of the carburetor, the other end is a finger portion which moves the valve, and both have adjustment screws which vary the opening time of the valve. The difference between the embodiments lies in the manner in which the arms are adjusted relative to and engage the accelerator pump flange, and this distinction will be made more apparent as the description proceeds.

Other objects and features of the invention will become apparent as the description proceeds in the specification, especially when taken in conjunction with the accompanying drawings, illustrating preferred embodiments of the invention, wherein:

FIG. 1 is an elevational view of a carburetor with parts broken away to illustrate the air inlet for air flow to the engine, the accelerator pump, and the pump discharge passage;

FIG. 2 is an enlarged sectional view taken along line 22 of FIG. 1, showing the fuel bowl vent valve and one embodiment of the adjustable vent valve operating arm; 1

FIG. 3 is a view similar to FIG. 2 and illustrates a second embodiment of the adjustable vent valve operating arm; and

FIG. 4 is an enlarged view taken along line 4-4 of FIG. 3 and showing the details of the adjustable vent valve operating arm.

Referring first to FIG. 1, the carburetor 10 has a mixture conduit 12 including an air inlet 14 and a mixture outlet 16 which discharges to the engine. A throttle 18 is disposed in mixture outlet 16 in the usual manner on the throttle shaft 20.

Mixture conduit 12 has a venturi-type restriction 22 formed between inlet 14 and outlet 16 of the mixture conduit 12, but it should be noted that the present invention need not be restricted to carburetors of the venturi type. For example, it could be used as well in an air valve carburetor having a covered fuel bowl, an accelerator pump, and linkage between the throttle and pump.

Continuing with the description of FIG. 1, a throttle lever 24 is secured to throttle shaft 20. A link 26 is pivotally connected at one end 28 to throttle lever 24. The other end 30 of link 26 is pivotally connected to one end 32 of an accelerator pump lever 34. Pump lever 34 is pivoted on carburetor 10 by means of a pivot pin 36. The opposite end 38 of pump lever 34 abuts an end 40 of a pump stem 42, thus operatively connecting throttle lever 24, link 26, pump lever 34 and pump stem 42.

An accelerator pump assembly 44 comprises pump stem 42 centrally and reciprocably disposed through a guide portion 46 formed in the fuel bowl cover 47 of carburetor l0. Slidably disposed on the lower end 48 of stem 42 is a pump plunger 50. Plunger 50 is disposed in a vertical pump bore 52 formed in carburetor l0 and has a cup seal member 54 abutting but slidingly disposed in pump bore 52. Cup seal 54 acts as a fuel check valve in a manner to be described.

Plunger 50 is urged toward its uppermost position by means of a return spring 56, one end of which resides in the bottom of bore 52 and the other end of which abuts the lower side of plunger 50, thereby urging plunger 50 upwardly.

The rate of discharge of fuel from a discharge portion 58 of bore 52 formed between plunger 50 and the bottom of the bore 52 is controlled in part by a stiff duration spring 60. The lower end '61 of duration spring 60 resides on a flange 62 radially extending from plunger 50. The upper end of duration spring 60 is restrained and compressed by means of a spring retainer 64 residing under a flange 82 on a shoulder portion 63 of pump stem 42.

In operation, when plunger 50 moves upward in pump bore 52, fuel flows from the fuel bowl 65 through a slot 66 in the top of the pump bore 52 and is passed by the skirt of the cup seal 54 into the discharge portion 58. It should be noted that in a preferred embodiment cup seal 54 is a so-called floating type, whereby cup seal 54 slides up and down on a tapered portion 67 of plunger 50. When the plunger 50 is moved upward, the flat 68 on the top of the cup seal 54 unseats from the associated flat on the plunger 50. This vents vapors which otherwise may be trapped in discharge portion 58 so that a solid charge of fuel can be maintained beneath plunger 50 for subsequent pump strokes. when plunger 50 is lowered, flat 68 on cup seal 54 seals against the associated flat on the plunger and the skirt on cup seal 54 is biased outwardly against the wall of bore 52 to prevent fuel flow therearound. In this manner, cup seal 54 acts as a fuel check valve for filling discharge portion 58.

A pump discharge passage 70 connects discharge portion 58 through a pump jet 72 to mixture conduit 12. During high speed operation, a vacuum exists on the downstream side of pump jet 72. Therefore, a cavity 74 upstream of pump jet 72 is provided which vents discharge passage 70 to the atmosphere outside the air inlet 14. Cavity 74 acts as a suction breaker so that when the pump 44 is not in operation, fuel will not be pulled out of pump jet 72 into the venturi area 22. This suction breaker ensures a full pump discharge when needed and prevents any siphoning or fuel pullover from pump 44 and discharge passage 70.

A discharge check ball 76 is disposed in discharge passage 70 and is vertically constrained by a ball retainer 77 which allows ball 76 to rise a selected height above a seat 79 formed in passage 70. During upward motion of plunger 50, check ball 76 is drawn against and thereby scals seat 79 so that air will not be drawn into discharge portion 58.

When throttle valve 18 is opened, the connecting linkage comprising lever 24, link 26 and lever 34 forces stem 42 and duration spring 60 downward. Stem 42 may move relative to plunger 50 by means of a recess 80 in the plunger. Spring 60 in turn forces plunger 50 downward at a rate determined, in part, by the stiffness of spring 60 and the size of passage 70. As soon as plunger 50 moves, it displaces fuel upwardly which seats pump cup 54 on radially extending flange 62 of plunger 50. The further downward movement of plunger 50 forces fuel from discharge portion 58 of bore 52 through the fuel discharge passage 70. Thereupon, fuel flow unseats check ball 76 and passes on through passage 70 to pump jet 72 for delivery to mixture conduit 12.

When the throttle is closed this repositions lever 24, link 26 and lever 34 to the position shown in FIG. 1.

Accordingly, spring 56 is effective to move plunger 50 upwardly and in turn this moves the lower end of spring 60 upwardly. This moves spring retainer 64 upwardly until spring 56 has fully expanded and stem 42 and retainer 64 are an aan uppermost position as shown in FIG. 1.

Referring to FIG. 2, the present invention will now be described in detail. A radially extending actuating plate or flange 82 is attached to or extends from spring retainer 64. Alternatively, flange 82 may reside between a shoulder portion 63 of stem 42 and retainer 64. A resilient valve operating arm 86 is secured at one end 87 to the underside of the cover 47 of fuel bowl 65. Operating arm 86 threadedly carries an adjusting screw 88 which engages flange 82 and lifts arm 86 as stem 42 nears its uppermost position during throttle closing movement. It should be noted that the resiliency or downward bias of arm 86 offers negligible resistance to the upward movement of stem 42.

The other end of arm 86 is a curled finger 89 which smoothly engages a valve disc 90 seated on a valve seat 92 formed in or staked to the cover 47 of the fuel bowl 65. This coaction between disc 90 and seat 92 seals an aperture 93 opening from a fuel vapor region 94 formed below cover 47 within bowl 65, When the throttle is closed and stem 42 is raised by spring 56, adjusting screw 88 carried on arm 86 is engaged by flange 82 and arm 86 moves upwardly. Thereupon, finger 89 slides under and smoothly lifts disc from seat 92. This permits fuel vapor to flow out of the fuel vapor region 94 through an opening 95 and a cavity 96 formed in cover 47 to a hose fitting 98 which is connected, for example, to a fuel vapor storage canister 99. The sliding action between finger 89 and disc 90 ensures that the venting process will proceed smoothly and unrestricted.

As the pump stem 42 moves downwardly during throttle opening movement, arm 86 moves downwardly under an inherent spring force to a lower position. As arm 86 moves downward, finger 89 disengages disc 90. This permits disc 90 to seat on valve seat 92 to prevent vapor flow from region 94 through aperture 93, opening 95 and cavity 96 to vapor storage canister 99.

However, valve disc 90 is, in the preferred embodiment, fashioned from light metal so as to be also responsive to bowl vapor pressure. Should the vapor pressure in vapor region 94 become adequate to overcome the weight of disc 90, the valve is forced upwardly to open aperture 93. Accordingly, excess vapor pressure is allowed to vent from region 94 through aperture 93, opening 95 and cavity 96 to vapor storage canister 99. This continues until the vapor pressure below valve 90 is reduced to a point where it is insufficient to raise the disc, thereby allowing the valve to close.

It should also be noted that disc 90 is free to rotate or float in a chamber 100 above aperture 93, so that the propensity for valve 90 to stick to seat 92 is minimized. A boss 101 extending downwardly in chamber 100 limits the vertical travel of the disc.

It should be noted that as screw 88 is turned it moves and thus varies the interengagement position between screw 88 and flange 82. This in turn varies the time in the accelerator pump return stroke at which flange 82 engages screw 88 and disc 90 is lifted. For example, if screw 88 is turned downwardly it will engage flange 82 at a lower point in the pump upward travel than would occur if screw 88 had been moved upwardly. Accordingly, arm 86 and finger 89 will move earlier during the pump return stroke or, more significantly, farther from closed throttle. and open the valve before the pump reaches its uppermost position.

It can therefore be seen that a continuum of interengagement points between screw 88 and flange 82 is available and is limited only by the length and position of screw 88 thereby providing a range of opening times of valve disc 90 relative to throttle position, which permits venting at a certain throttle position, at or near closed throttle. Accordingly, fuel vapor, which the engine may not be capable of completely burning if it were discharged through internal vent passages may be vented away from the carburetor.

An alternative embodiment of the present invention is shown in FIG. 3, in which a modified form of the valve actuating spring 86 is designated 86'. It should be recognized that the environment of the arm is identical to that heretofore described, and modified components comprising the present invention are designated with primed reference numerals in the FIG. 3 embodiment.

Proceeding with the details of FIG. 3, spring arm 86' is secured at one end 87 to the cover 47' of the fuel finger portionfli89' which is disposed off-center of the .valve .disc 90. It should be appreciatedthat the curled finger 89' is provided to open valve disc 90 in the manner, illustrated by the phantom position of arm-8 6'. The curled finger,89f.-slides smoothly under valve disc 90. This sliding action ensures that the venting process will proceed-smoothly and unrestricted. Abos s101 extending downwardly into chamber 100 above-disc 90 limits the travel of disc.;9 0 in a manner identical to theFlG. 2 embodiment. 1

Spring arm 86 extends back upon itself about curled finger 89" in 'a conforming manner and forms an inter mediate humpedportion; 102 which extends downwardly to a tang 104. Tang 104 extends through an aperture 1-06 formed'in thelower portion 108 of arm 86 and may abut and engage radially extending flange 82 ridingon spr'ing retainer. 64, When'flange 82 engages tang 104, this moves arm 86' aiid raises finger portion 89' to engage: valve disc 90. Accordingly, vapors in region 94 mayflow through apertufe 93,,opening 95 and cavity 96 to vapor storage'ca nis'ter 9 9. l M

An adjustment screw 88" is threadedly carried by humped portion 102 and abuts the lowe r portion 108 of spring arm 86". Asl'adjustment screw 88 "is turned, it lifts the humped portion 102 from the lowerportion s of arm 86. Accordingly, tang 104 is raised relative to curled finger portion 89. This adjusts the position of finger 89 relative to flange 82 to control the time of opening of valve 90 in a manner analogous to the FIG. 2 embodiment.

Referring to FIG. 4, further details of the spring arm 86 can be observed. Fixed end 87 of the arm is secured to the cover 47 of fuel bowl 65 by means of two screws 110. Aperture 106, formed in the lower portion 108 of the spring arm 86, allows movement of the arm about pump stem 42. Downwardly extending tang 104 protrudes through aperture 106 to engage the radially extending flange 82 carried by retainer 64. Adjustment screw 88' is shown in phantom above the lower portion 108 of arm 86. Lower portion 108 extends to the curled finger 89 and turns back upon itself so that it resides under the upper or humped portion 102 of the arm.

Adjustment of the operating arm in either embodiment is facilitated by an opening 111 formed in cover 47 through which a driver may be inserted to turn screw 88 (88) after the carburetor is assembled. A cover plate or plug 112 may be used to sealingly close opening 111 after adjustment is completed to prevent loss of fuel vapor therethrough.

Thus, it will be seen that in accordance with the invention, a carburetor fuel bowl vent valve 90 is operated when the accelerator pump 44 is in its uppermost position by means of an adjustable, resilient operating arm 86 (86'). It should be noted that adjustment screw 88 (88') is threadedly carried by the arm to adjust the position of the arm relative to the pump stern flange to ensure venting of the carburetor fuel bowl whenever the pump is in its uppermost position. i A

Although the preferred embodiments and method of operation of the present invention have been described, the present invention is not to be limited by the foregoing description, but as set forth in the hereinafter appended claims.

What is claimed is:

1. An internal combustion engine carburetor having an air inlet for air flow to the engine, a throttle disposed in said air inlet and movable between closed and open positions for. controlling air flow therethrough, a fuel bowl, said fuel bowl having a fuel vapor region in its upperportion, a cover member for said fuel bowl said cover member having a vent aperture opening from said region for discharging fuel vapor therefrom and a valve seat surrounding said aperture, a vent valve biased into engagement with said valve seat for controlling the flow of fuel vapor throughsaid aperture, an accelerator pump bore vertically disposed in said carburetor, an accelerator pump plunger disposed in said bore and defining a discharge chamber within said bore, inlet means for supply fuel from said fuel bowl to said chamber, a discharge passage for delivering fuel from saidchamber'to said air inlet, a stem for reciprocating said plunger within said bore to discharge fuel from said chamber through said passage to said inlet when said stern moves downwardly, said stem having a radially extending flange, and. linkgage means operatively connecting said stem with said throttle for moving said stem upwardly as said throttle is moved to said closed position and downwardly as said throttle is moved to said open position, wherein the improvement comprises: a resilient valve operating arm movable between a lower and a'raised position, said arm having one end secured to said cover member, said arm having another end engageable with said vent valve when said arm is in said raised position, said arm including means which engages said flange only when said pump is near its uppermost position to lift said arm to said raised position whereby said other end of said arm engages and lifts said valve from said valve seat, said arm being biased from said raised position whereby said arm returns to said lower position and disengages said valve when said pump is below said position.

2. An internal combustion engine carburetor having an air inlet for air flow to the engine, a throttle disposed in said air inlet and movable between closed and open positions for controlling air flow therethrough, a fuel bowl, said fuel bowl having a fuel vapor region in its upper portion, a cover member for said fuel bowl having a vent aperture opening from said region for discharging fuel vapor therefrom and a valve seat surrounding said aperture, a vent valve biased into engagement with said valve seat for controlling the flow of fuel vapor through said aperture, an accelerator pump bore vertically disposed in said carburetor, an accelerator pump plunger disposed in said bore and defining a discharge chamber within said bore, inlet means for supplying fuel from said fuel bowl to said chamber, a discharge passage for delivering fuel from said chamber to said air inlet, a stem for reciprocating said plunger within said bore to discharge fuel from said chamber through said passage to said inlet when said stem moves downwardly, said stem having a radially extending flange, and linkage means operatively connecting said stem with said throttle for moving said stem upwardly as said throttle is moved to said closed position and downwardly as said throttle is moved to said open position, wherein the improvement comprises: a resilient valve operating arm having one end disposed adjacent said valve and having the other end secured to the underside of said cover member, said arm being movable between a lowered and a raised position, and an adjustment screw theadedly carried by said arm and engaging said flange of said stern as said throttle is moved toward said closed position whereby said arm is raised from said lowered position to engage and lift said valve from said valve seat, said screw disengaging said flange as said throttle is moved from said closed position whereby said arm is lowered from said raised position and is disengaged from said valve.

3. An internal combustion engine carburetor having an air inlet for air flow to the engine, a throttle disposed in said air inlet and movable between closed and open positions for controlling air flow therethrough, a fuel bowl, said fuel bowl having a fuel vapor region in its upper portion, a cover member for said fuel bowl having a vent aperture opening from said region for discharging fuel vapor therefrom, and a valve seat surrounding said aperture, a vent valve biased into engagement with said valve seat for controlling the flow of fuel vapor through said aperture, an accelerator pump bore vertically disposed in said carburetor, an accelerator pump plunger disposed in said bore and defining a discharge chamber within said bore, inlet means for supplying fuel from said fuel bowl to said chamber, a discharge passage for delivering fuel from said chamber to said air inlet, a stem for reciprocating said plunger within said bore to discharge fuel from said chamber through said passage to said inlet when said stem moves downwardly, said stem having a radially extending flange, and linkage means operatively connecting said stem with said throttle for moving said stem upwardly as said throttle is moved to said closed position and downwardly as said throttle is moved to said open position wherein the improvement comprises: a resilient valve operating arm having one end secured to the underside of said cover member and the other end forming a finger portion, said arm having a lower portion with an aperture formed therein, said stem protruding through said aperture, said arm further having an upper humped portion carrying a tang extending downwardly through said aperture to engage said flange, said upper humped portion disposed above said lower portion between said secured end and said finger portion, said arm being movable between a lowered and a raised position, and an adjusting screw threadedly carried by said upper humped portion and abutting said lower portion, whereby said adjusting screw moves said hump portion relative to said lower portion to reposition said tang thereby varying the time at which said tang engages said flange as said throttle is moved toward said closed position, and whereby as said throttle is moved toward said closed position said tang is moved by said flange and raises said arm to said raised position so that said finger portion opens said valve, and as said throttle is moved away from said closed position said tang disengages said flange and said arm is lowered from said raised position and is disengaged from said valve.

l l l

Claims

1. A INTERNAL COMBUSTION ENGINE CARBURETOR HAVING AN AIR INLET FOR AIR FLOW TO THE ENGINE, A THROTTLE DISPOSED IN SAID AIR INLET AN MOVABLE BETWEEN CLOSED ANDOPEN POSITIONS FOR CONTROLLING AIR FLOW THERETHROUGH, A FUEL BOWL, SAID FUEL BOWL HAVING A FUEL VAPOR REGION IN ITS UPPER PORTION, A COVER MEMBER FOR SAID FUEL BOWL, SAID COVER MEMBER HAVINGA VENT APERTURE OPENING FROM SAID REGION FOR DISCHARGING FUEL VAPOR THEREFROM AND A VALVE SEAT SURROUNDING SAID APERTURE, A VENT VALVE BIASED INTO ENGAHEMENT WITH SAID VALVE SEAT FOR CONTROLLING THE FLOW OF FUEL VAPOR THROUGH SAID APERTURE, AN ACCELERATOR PUMP BORE VERTICALLY DISPOSED IN SAID CARBURETOR, AN ACCELERATOR PUMP PLUNGER DISPOSED IN SAID BORE AND DEFINING A DISCHARGE CHAMBER WITHIN SAID BORE, INLET MEANS FOR SUPPLY FUEL FROM SAID FUEL BOWL TO SAID CHAMBER, A DISCHARGE PASSAGE FOR DELIVERING FUEL FROM SAID CHAMBER TO SAID AIR INLET, A STEM FOR RECIPROCATING SAID PLUNGER WITHIN SAID BORE TO DISCHARGE FUEL FROM SAID CHAMBER THROUGH SAID PASSAGE TO SAID INLET WHN SAID STEM MOVES DOWNWARDLY, SAID STEM HAVING A RADIALLY EXTENDING FLANGE, AND LINKGAGE MEANS OPERATIVELY CONNECTING SAID STEM WITH SAID THROTTLE FOR MOVING SAID STEM UPWARDLY AS SAID THROTTLE IS MOVED TO SAID CLOSED POSITION AND DOWNWARDLY AS SAID THROTTLE IS MOVED TO SAID OPEN POSITION, WHEREIN THE IMPROVEMENT COMPRISES: A RESILIENT VALVE OPERATING ARM MOVABLE BETWEEN A LOWER AND A RAISED POSITION, SAID ARM HAVING ONE END SECURED TO SAID COVER MEMBER, SAID ARM HAVING ANOTHER END ENGAGEABLE WITH SAID VENT VALVE WHEN SAID ARM IS IN SAID RAISED POSITION, SAID ARM INCLUDING MEANS WHICH ENGAGES SAID FLANGE ONLY WHEN SAID PUMP IS NEAR ITS UPPERMOST POSITION TO LIFT SAID ARM TO SAID RAISED POSITION WHEREBY SAID OTHER END OF SAID ARM ENGAGES AND LIFTS SAID VALVE FROM SAI VALVE SEAT, SAID ARM BEING BIASED FROM SAID RAISED POSITION WHEREBY SAID ARM RETURNS TO SAID LOWER POSITION AND DISENGAGES SAID VALVE WHEN SAID PUMP IS BELOW SAID POSITION.

2. An internal combustion engine carburetor having an air inlet for air flow to the engine, a throttle disposed in said air inlet and movable between closed and open positions for controlling air flow therethrough, a fuel bowl, said fuel bowl having a fuel vapor region in its upper portion, a cover member for said fuel bowl having a vent aperture opening from said region for discharging fuel vapor therefrom and a valve seat surrounding said aperture, a vent valve biased into engagement with said valve seat for controlling the flow of fuel vapor through said aperture, an accelerator pump bore vertically disposed in said carburetor, an accelerator pump plunger disposed in said bore and defining a discharge chamber within said bore, inlet means for supplying fuel from said fuel bowl to said chamber, a discharge passage for delivering fuel from said chamber to said air inlet, a stem for reciprocating said plunger within said bore to discharge fuel from said chamber through said passage to said inlet when said stem moves downwardly, said stem having a radially extending flange, and linkage means operatively connecting said stem with said throttle for moving said stem upwardly as said throttle is moved to said closed position and downwardly as said throttle is moved to said open position, wherein the improvement comprises: a resilient valve operating arm having one end disposed adjacent said valve and having the other end secured to the underside of said cover member, said arm being movable between a lowered and a raised position, and an adjustment screw theadedly carried by said arm and engaging said flange of said stem as said throttle is moved toward said closed position whereby said arm is raised from said lowered position to engage and lift said valve from said valve seat, said screw disengaging said flange as said throttle is moved from said closed position whereby said arm is lowered from said raised position and is disengaged from said valve.