GB1560109A

GB1560109A - Idling mixture adjusting device of carburettor

Info

Publication number: GB1560109A
Application number: GB5333076A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1975-12-26
Filing date: 1976-12-21
Publication date: 1980-01-30

Description

(54) IMPROVED IDLING MIXTURE ADJUSTING DEVICE OF CARBURETOR (71) We, NISSAN MOTOR COMPANY. LIMITED a corporation organized under the laws of Japan, of No. 2, Takaramachi, Kanagawa-ku, Yokohama City, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a device for adjusting the idling speed mixture produced by a carburetor of an internal combustion engine.

It is the main object of the present invention to provide an improved idling mixture adjusting device of a carburetor of an internal combustion engine, by which device an unnecessary change of the idling mixture may be made impossible to prevent the emission of noxious gases from the engine into the circumferential air.

Another object of the present invention is to provide an improved idling mixture adjusting device of a carburetor of an internal combustion engine, by which device usual drivers cannot unnecessarily change the setting of the idling mixture, but the idling mixture may be changed and adjusted when necessary with a particularly designed adjusting tool which may be provided in service stations.

According to the present invention, there is provided a combination comprising: an idling mixture adjustment screw turnably and operatively installed in a carburetor of an internal combustion engine, for adjusting an air-fuel mixture supplied to the engine during idling of the engine when turned, the adjustment screw being formed with a head having first means engageable by a turning tool; a turning tool for turning the head of the adjustment screw, the turning tool being formed with an end portion having second means which is engageable with the first means of the adjustement screw to turn the adjustment screw after the second means engages with the first means; and a covering member for covering the head of the idling adjustment screw and being formed with a slot through the wall of the covering member, the slot being generally in the shape which is produced by projecting the maximum cross-section of the second means of the turning tool on the surface of the covering member, so that the second means is just capable of passing through the slot to reach and engage with the first means.

Other objects, features and advantages of the present invention will become more apparent from the following description of the various examples thereof, taken in conjunction with the accompanying drawings in which like reference numerals designate like parts and elements throughout the various examples, in which:: Fig. 1 is a vertical section view of a prior art idling mixture adjusting device; Fig. 2 is a section view taken in the direction of the arrows substantially along the line I-I of Fig. 1; Fig. 3 is a perspective view of the prior art idling adjusting device of Fig. 1; Fig. 4 is a vertical section view of a fixed-venturi carburetor incorporating therein a preferred example of an idling mixture adjusting device according to the present invention; Fig. 5 is an enlarged plan view showing the idling mixture adjusting device of Fig. 4; Fig. 6 is a vertical section view of the device of Fig. 5; Fig. 7 is a perspective illustration showing the device of Fig. 5; Fig. 8 is an enlarged plan view of a modified example of the idling mixture adjusting device of Fig. 4; Fig. 9 is a perspective illustration showing the device of Fig. 8;; Fig. 10 is a perspective illustration of another modified example of the idling mixture adjusting device of Fig. 4; Fig. 11 is a vertical section view of the fixed-venturi carburetor incorporating therein another example of the idling mixture adjusting device in accordance with the present invention; Fig. 12 is an enlarged plan view of the idling mixture adjusting device showing the device of Fig. 11; Fig. 13 is a vertical section view showing the device of Fig. 12; Fig. 14 is a perspective illustration showing the device of Fig. 12; Fig. 15 is an enlarged plan view of a modified example of the idling mixture adjusting device of Fig. 11; Fig. 16 is a perspective illustration showing the device of Fig. 15; Fig. 17 is a perspective illustration of another modified example of the idling mixture adjusting device of Fig. 11;; Fig. 18 is a perspective view of a further modified example of the idling mixture adjusting device of Fig. 11; Fig. 19 is a vertical section view of a variable-venturi carburetor incoporating therein a further example of the idling mixture adjusting device in accordance with the present invention; and Fig. 20 is an enlarged vertical section view showing the idling mixture adjusting device of Fig. 19.

Modern carburetors for an internal combustion engines are provided with idling adjustment screws for adjusting an idling mixture supplied to the combustion chambers of the engine. The idling adjustment screw is usually such precisely set, using exhaust gas analyzer equipment in factories or service stations, to ensure that the carburetor supplies the combustion chambers of the engine with the idling mixture having an air-fuel ratio appropriate for noxious gas emission control. However, the thus set idling adjustment screw may easily be turned by drivers or other physical forces applied thereto to change the air-fuel ratio of the idling mixture. This change of the air-fuel ratio may cause undesirable high emission levels of the noxious gases.

In view of the above fact, a device for limiting the turning movement of the idling mixture adjustment screw has been proposed to prevent an excess turning of the adjustment screw.

An example of the turning movement limiting device is shown in Figs. 1 to 3 which illustrate a prior art idling mixture adjusting device, in which the screw head 10a of an idling adjustment screw 10 is securely covered with a limiter cap 12 which is provided with a plurality of members 14 which engage slots in the periphery of the screw head 10a. The limiter cap 12 is formed with a projection 16 which is engageable with a stop 18 secured to the body of a carburetor (not shown). With this arrangement, only about one turn of the idling adjustment screw is permitted and therefore a considerable deterioration of the emision control is prevented.

However, a problem has arisen with such a limiting device as mentioned hereinbefore, in which an appropriate air-fuel ratio of the idling mixture may not be obtained due to the limitation of turning of the adjustment screw when the atmospheric temperature and pressure are considerably changed from the levels at which the adjustment screw was set, such as during extremely cold and hot weather and high altitude ground cruising. If the limiter cap can be removed, the adjustement of the idling mixture during such conditions will be easily accomplished, but the limitation of turning the adjustment screw only one turn will not be present.

Therefore, the present invention contemplates that the idling mixture adjustment screw cannot be turned by usual drivers with usual tools, but can be turned with particular tools prepared, for example, in the service stations. This fact makes possible the adjustment of the idling mixture when required although the idling mixture adjustment is usually impossible.

Referring now to Fig. 4 of the drawings, there is shown a fixed-venturi (choke) carburetor, generally designated by the reference numeral 20, incorporating therein a preferred example of a device 22 for adjusting the air-fuel ratio of the air-fuel mixture or the idling mixture supplied from the carburetor 20 into the combustion chambers of an internal combustion engine (not shown) during idling of the engine.

The carburetor 20 comprises, as usual, a main discharge nozzle 24 opening into a venturi portion 26 disposed upstream of a throttle valve 28 which is pivotally disposed in an air-fuel mixture induction passage 30 which communicates with the combustion chambers of the engine. The main discharge nozzle 24 is connected by a fuel passageway 32 of the main fuel circuit (no numeral) with a float bowl 34 filled with a fuel such as gasoline (petrol). As customary, the fuel passageway 32 communicates through a fuel passageway 36 of the idling system (no numeral) with a slow running port 38 opening into the air-fuel mixture induction passage 30 and adjacent the edge of the throttle valve 28.The slow running port 38, in turn, communciates with an idling mixture discharge port 40 opening into the air-fuel mixture induction passage 30 down-stream of the slow running port 38 and the throttle valve 28 to supply the fuel into the air-fuel mixture induction passage 30 during idling of the engine.

Reference numeral 42 indicates an idling adjustement screw forming part of the idling mixture adjusting device 22 and is composed of a threaded portion 42a movably engaged with the body of the carburetor 20, a head 42b integral with one end of the threaded portion 42a and a needle valve portion 42c integral with the other end of the threaded portion 42a and located adjacent the idling mixture discharge port 40.This adjustment screw 42 is, as usual, arranged to control the amount of fuel discharged through the idling mixture discharge port 40 into the air-fuel mixture induction passage 30 such that the amount of the discharge fuel is decreased as the needle valve portion 42c is advanced or moved in the direction of the discharge port 40 by turning the head 42b to decrease the cross-sectional area of the discharge port 40, whereas the amount of the same is increased as the needle valve portion 42c is withdrawn or moved in the opposite direction of the discharge port 40. Covering the head 42b of the idling mixture adjustment screw 42 is a cap 44 or a covering member 44 which is movably secured to the threaded portion 42a of the idling mixture adjustment screw 42.

Figs. 5 to 7 show in detail the idling mixture adjusting device 22 in which the cap 44 is composed of a cylindrical portion 44a surrounding the head 42b, a flange portion44b integral with one end of the cylindrical portion 44a, and a circular lid portion 44c integral with the other end of the cylindrical portion 44a. The flange portion 44b may be formed by a plurality of inwardly directed, radially disposed, pointed rods. The cap 44 is turnably secured to the surface of the threaded portion 42a of the adjustment screw 42 in such a manner that the flange portion 44b is disposed within an annular groove 46a formed in the peripheral surface of a cylindrica collar 46 which is disposed around the threaded portion 42a of the adjustment screw 42.Additionally, the cylindrical collar 46 is urged to contact with the bottom surface of the head 42b by a coiled spring 48 seated on the body of the carburetor 20. It is to be noted that the cap 44 can be easily and smoothly turned around the screw head 42b by the effect of the cylindrical collar 46 which is made, for example, of nylon, when a turning force is applied thereto. In this example, the head 42b is formed at its top surface with a conical portion 50 as best seen in Fig. 7. On the surface of the conical portion 50, two straight grooves 52a and 52b or first means engageable by a turning tool hereinafter described are formed and connected to each other at the vertex of the conical portion 50. Each of the two straight grooves 52a and 52b extends from the vertex of the conical portion to the periphery of the head 42a.The two straight grooves 52a and 52b are aligned straight as clearly shown in Fig. 5.

Indicated by the reference numeral 54 is a turning tool or an adjusting tool for turning the idling adjustment screw 42 to adjust the air-fuel ratio of the idling mixture. The turning tool 54 has at its one end two finger-like members 54a and 54b or second means which is engageable with the grooves 52a and 52b of the idling adjustment screw 42. While the one end of the turning tool 54 is formed into a Y-shape in this example, it may be formed into a shape which is produced by cutting off a V-shaped portion of the edge of a screw-driver having a flat edge. The cap 44 has at its circular lid portion 44c a slot 56 in the shape which is preduced by projecting the finger-like members 54a and 54b from the direction of an arrow a on the surface of the circular lid portion 44c and accordingly the shape is of a straight line as shown.The area of the slot 56 defined on the surface of the circular lid portion 44c of the cap 44 is formed generally the same as the projected area of the finger-like members 54a and 54b, or slightly larger than the projected area in order to smoothly pass the finger-like members 54a and 54b of the adjusting tool 54 through the slot 56 of the cap 44.

With the arrangement hereinbefore described, when an adjustment or change of the air-fuel ratio of the idle mixture is required, the finger-like members 54a and 54b of the adjusting tool 54 are inserted through a slot 56 into the cap 44 and thereafter the cap 44 is turned until the slot 56 of the cap 44 aligns with the grooves 52a and 52b of the idling adjustment screw 42 if the both are not in alignment with each other, for example, as shown in Fig. 5. Subsequently, the finger-like members 54a and 54b of the adjusting tool 54 reach and engage with the groves 52a and 52b formed on the surface of the head 42b of the idling adjustment screw 42. In this state, the idling adjustment screw 42 is turned, by turning the adjusting tool 54, to an extent required for obtaining an appropriate air-fuel ratio of the idling mixture.

It will be understood from the foregoing, that the idling adjustment screw 42 cannot be turned and therefore the idling mixture cannot be adjusted or changed without the use of the particularly designed adjusting tool mentioned above. If drivers intend to turn the idling adjustment screw 42 with a screw-driver having a flat edge, the edge of the screw driver may pass through the slot 56 formed at the cap 44 to contact the vertex of the conical portion 50 of the adjustment screw 42, but cannot turn the adjustment screw 42 since the edge of the screw-driver will only engage the vertex portion of the screw head 42b. Of course, even if the cap 44 is forced to turn, only the cap 44 itself turns around the threaded portion 42a of the adjustment screw 42 and therefore the adjustment of the idling mixture is impossible.

However, using the above-mentioned particularly designed adjusting tool 54, the one end of the adjusting tool 54 fits and engages with the grooves 52a and 52b formed on the surface of the head 42b of the idling adjustment screw 42 and therefore the adjustment screw 42 may be easily turned to adjust or change the idling mixture. Accordingly, the air-fuel ratio of the idling mixture may be adjusted or changed as occasion demands if the particular adjusting tool 54 is supplied in factories and service stations equipped with exhaust gas analyzers.

Figs. 8 and 9 show a modified example of idling mixture adjusting device 22 which is similar to the example shown in Figs. 5 to 7. In the device 22, the conical portion 50 of the head 42b of the adjustment screw 42 has four straight grooves 58 formed on the surface thereof. Each of the four straight grooves 58 extends from the vertex of the conical portion 50 to the periphery of the head 42b.

With this connection, the adjusting tool 54 is formed at its one end four finger-like members 60 which are respectively engageable with the four straight grooves 58 of the adjustment screw 42. Additionally, the circular lid portion 44c of the cap 44 is formed with the slot 56' of a shape produced by projecting the four finger-like members 60 of the adjusting tool 54 in the direction of the arrow a on the surface of the circular lid portion 44c of the cap 44 and accordingly the shape of the slot 56' is of a cross in this example as seen in Fig. 8. It will be understood that the four straight grooves 58 of the idling adjustment screw 42 of this example are arranged such that adjacent two grooves constitute the right angle therebetween.

With this arrangement, turning of the adjustment screw 42 by the adjusting tool 54 is more positive than in the example shown in Figs. 5 to 7, because if a part of the grooves 58 is worn, the remaining grooves securely engage with the finger-like members 60 of the adjusting tool 54. It will be appreciated that the idling adjustement screw 42 having four grooves 58 shown in Fig. 9 may be turned with the adjusting tool 54 having two finger-like members 54a and 54b as shown in Fig. 7.

Fig. 10 shows the head 42b of another modified example of the idling mixture adjusting device 22. The head 42b is similar to one shown in Fig. 7 except that two straight elongate projections 62a and 62b are formed on the surface of the conical portion 50 of the head 42b instead of the two straight grooves 52a and 52b shown in Fig. 7. It will be understood that the projections 62a and 62b may be engageable at their sides with the sides of the adjusting tool 54 mentioned hereinbefore, and accordingly the idling adjustment screw 42 shown in Fig. 10 may be turnable with the adjusting tools shown in Figs 7 and 9.

Fig. 11 illustrates another example of the idling mixture adjusting device 22' which is incorporated with the carburetor the same as one shown in Fig. 4, in which like reference numerals to those in Fig. 4 represent like parts and elements for the purpose of simplicity of illustration. The cap 44 or the covering member is composed of a cylindrical member 64 which surrounds the head 42b of the idling adjustment screw 42. The cylindrical member 64 is formed at its one end with a flange portion 64a and at the other end with an annular groove 64b. The flange portion 64a is, as shown, contactable with the bottom surface of the head 42b and urged in the direction to contact the head 42b by the coiled spring 48 seated on a portion of the carburetor body. A disc member 66 is turnably disposed or received at the annular groove 64b of the cylindrical member 64.The disc member 66 is urged by a spring 68 disposed inside the cylindrical member 64 so that the free movement of the disc member 66 within the annular groove 64b is prevented. Secured to the outer surface of the cylindrical member 64 is a member 70 for preventing turning movement of the cylindrical member 64 with respect to the carburetor body.

Figs. 12 to 14 show in detail the idling mixture adjusting device 22' shown in Fig. 11, in which the member 70 frictionally engages the outer surface of the cylindrical member 64 slidably engages with a projection 20a of the carburetor body so that only the axial movement of the cylindrical member 64 is permited, i.e. the cylindrical member 64 is only movable longitudinally during axial movement of the screw 42. As best seen in Fig. 13, the spring 68 is seated on the annular spring seat (no numeral) formed at the peripheral portion of the head 42b. In this example, the head 42b of the idling adjustment screw 42 is formed at its top surface with the conical portion 50 on which surface the two straight grooves 52a and 52b are formed as seen in Fig. 14.With this arrangement, the turning tool 54 or the adjusting tool is formed, as seen in Fig. 14, with a generally Y-shaped bifurcate plate member 72 of which two plate members 72a and 72b are respectively engageable with the two grooves 52a and 52b of the idling adjustement screw 42. The bifurcate plate member 72 may be in the shape formed by cutting off a V-shaped portion of the edge of a screw-driver having a flat edge. Additionally, the disc member 66 is formed with the slot 56 in the shape of the straight line which shape is determined the same as in the example shown in Figs. 5 to 7. With this arrangement, the bifurcate plate member 72 is inserted through the slot 56 into the cap 44 and thereafter engaged with the grooves 52a and 52b of the idling adjustment screw 42. Then the idling adjustment screw 42 is turned the required amount with the adjusting tool 54.

Figs. 15 and 16 show a modified example of the idling mixture adjusting device 22', in which the head 42b of the adjustment screw 42 is formed at the surface of its conical portion with the four straight grooves 58 which are same as in the example shown in Fig. 9.

Additionally, the adjusting tool 54 is formed at its one end with the four finger-like members 60 which is same as in the example shown in Fig. 9. With this arrangement the disc member 66 has the slot 56' in the shape of the cross the same as in the example shown in Fig. 8. It will be understood that the four finger-like members 60 of the adjusting tool 54 are inserted through the cross-shaped slot 56' into the cap 44 to engage respectively with the four straight grooves 58 of the idling adjustment screw 42.

Fig. 17 shows the head 42b of another modified example of the idling mixture adjusting device 22' in which the head 42b is formed at the top surface of its conical portion 50 with the two straight elongate projections 62a and 62b which are same as in the example shown in Fig.

10.

Fig. 18 shows a further modified example of the idling mixture adjusting device 22' in which the top surface of the head 42b of the idling adjustment screw 42 is formed flat. As seen, the two opposite grooves 74a and 74b are formed on the top surface of the head 42b and extend from the central portion of the flat top surface to the periphery of the head 42b. With this arrangement, the adjusting tool 54 is formed at its one end with a bifurcate plate member 76 which has two plate portions 76a and 76b. The two plate portions 76a and 76b are respectively arranged to be engageable with the two opposite grooves 74a and 74b of the idling adjustment screw 42.

Figs. 19 and 20 illustrate a variable-venturi (choke) carburetor, represented by the refers ence numeral 78, of an internal combustion engine, incorporating therein a further example of the idling mixture adjusting device 22". The carburetor 78 is arranged such that the choke area of a venturi portion 80 is controlled by a movable piston 82 subjected to the vacuum of the intake air on its upper surface and atmospheric pressure on the opposite surface as known in the art to maintain the venturi vacuum constant. In this carburetor 78, indicated by the reference numeral 84 is a passageway connecting an air induction passage 86 upstream of the venturi portion 80 and the air induction passage 86 between the venturi portion 80 and a throttle valve 88 pivotally disposed within the air induction passage 86.Disposed in the passageway 84 is the idling mixture adjusting device 22" which will be described in detail hereinafter with reference to Fig. 20. In Fig. 20, the idling mixture adjusting device 22" is composed of the idling adjustment screw 42' which has a body portion 42a', and a head 42b' integral with the one end of the body portion 42a'. The other end of the body portion 42a' is formed into a valve head (no numberal). The idling adjustment screw 42' is movably screwed into the body of the carburetor 78 so that the valve head formed at the body portion 42a' of the screw 42' is contactable with a valve seat (no numeral) formed inside the passageway 84.

The covering member 44 surrounds and covers the head 42b' of the idling adjustment screw 42' and secured to the body of the carburetor 78 by fastening means 90 such as a machine screw or a rivet. Disposed turnably at the groove (no numeral formed adjacent the upper open end 92 of the cap 44 is a disc member 66 which is urged by a spring 94 seated on a flange portion 96 of the idling adjusting screw 42' in a direction to prevent free rotative movement of the disc member 66. The disc member 66 has the slot 56 of the shape corresponding to grooves or projections 98 formed on the top surface of the head 42b' of the idling adjustment screw 42'. While the shapes formed on the head 42b' and the slot 56 of the disc member 66 have not been clearly shown, it will be understood that the relationship of them is same as in the various examples shown and described hereinbefore.It will also be appreciated that the formation on the adjusting tool or the turning tool (not shown in this example) will be arranged to be engageable with the formation of the idle adjustment screw 42' after passing through the slot 56 of the disc member 66.

With the arrangement shown in Figs. 19 and 20, the cross-sectional area defined by the valve seat formed inside the passageway 84 is controlled by turning the idling adjustment screw 42' to control the amount of air supplied to the air induction passage 86 between the venturi portion 80 and the throttle valve 88.

Therefore, the air-fuel ratio of the idling mixture or mixture supplied during idling of the engine may be adjusted by turning of the idling adjustment screw 42' with the adjusting tool 54 used in the various examples described and shown hereinbefore.

It will be understood that since the cylindrical member 64 of the cap 44 in the embodiment shown in Figs. 11 through 20 is secured to the carburetor body so that the turning of the cylindrical member 64 is prevented, the idle adjustment screw 42 cannot be turned if the driver nips the cylindrical member 64 of the cap with a gripping tool such as pliers, or tongs. In this connection, the cap 44 of the embodiment shown in Figs. 4 to 10 is turnable around the idling adjustment screw 42 and accordingly the adjustment screw 42 may be unnecessarily turned with the gripping tool by the driver.

As is apparent from the foregoing discussion, according to the present invention, the drivers cannot turn the idling adjustment screw of the carburetor and accordingly cannot unnecessarily change the idling mixture which has been appropriately set in consideration of the control of noxious gas emission during idling of the engine. However, the idling mixture may be changed and adjusted when necessary by turning the adjustment screw with the particularly designed adjusting tool which is provided, for example, in service stations.

WHAT WE CLAIM IS: 1. A combination comprising: an idling mixture adjustment screw turnably and operatively installed in a carburetor of an internal combustion engine, for adjusting an air-fuel mixture supplied to the engine during idling of the engine when turned, said adjustment screw being formed with a head having first means engageable by a turning tool; a turning tool for turning the head of said adjustment screw, said turning tool being formed with an end portion having second means which is engageable with the first means of said adjustment screw to turn said adjustment screw after the second means engages with the first means; and a covering member for covering the head of said idling adjustment screw, said covering member having a slot formed through the wall of said covering member, said slot being generally in the shape which is produced by projecting the maximum cross-section of said second means of said turning tool on the surface of said covering member, so that the second means is just capable of passing through the slot to reach and engage the means.

2. A combination as claimed in Claim 1, in which said idle adjustment screw is movably disposed adjacent an idling mixture discharge port of a fixed-venturi carburetor of the engine to control the cross-sectional area of the idling mixture discharge port to control the fuel amount supplied from the idling mixture discharge port into the air-fuel mixture induction passed of the carburetor, the idling mixture discharge port communicating with the float bowl of the carburetor and opening into the air-fuel mixture induction passage downstream of a throttle valve of the carburetor.

3. A combination as claimed in Claim 2, in which said covering member includes a cylindrical portion disposed to surround the head of said idling mixture adjustment screw and turnably secured at its one end to said idling mixture adjustment screw, and a circular lid portion integral with the other end of said cylindrical portion, the slot being formed through said lid portion.

4. A combination as claimed in Claim 3, in which said covering member includes a radial flange portion integral with the one end of said cylindrical portion.

5. A combination as claimed in Claim 4, including a cylindrical collar disposed around said idling adjustment screw and having an annular groove formed along the peripheral surface thereof, the radial flange portion of said covering member being disposed within the annular groove.

6. A combination as claimed in Claim 3, in which the head of said adjustment screw is formed, at its top surface, with a conical portion, said first means of said idling adjustment screw including two straight grooves formed on the surface of the conical portion of said head, each of the two straight grooves extending from the vertex of the conical portion to the periphery of the screw head, and the second means of said turning tool including two finger-like members which are respectively engageable with the two straight grooves of the conical portion of said idling adjustment screw.

7. A combination as claimed in Claim 3, in which the head of said idling adjustment screw is formed, at its top surface, with a conical portion, said first means including four straight grooves formed on the surface of the conical portion of the head, each of the four straight grooves extending from the vertex of the conical portion to the periphery of the head, and the second means including four finger-like members which are respectively engageable with the four straight grooves of the conical portion of said idling adjustment screw.

8. A combination as claimed in Claim 3, in which the head of said idling adjustment screw is formed, at its top surface, with a conical portion, said first means of said idling adjustment screw including two straight elongate projections formed on the surface of the conical portion, each of the projections extending from the vertex of the conical portion to the periphery of the head.

9. A combination as claimed in Claim 2, in which said covering member includes a cylindrical member disposed to surround the head of said idling adjustment screw and non-rotatably mounted on the body of the carburetor, but capable of axial movement relative thereto, the cylindrical portion being contactable at its one end with the head and having an annular groove formed at the other end thereof, and a disc member turnably received in the annular groove of the cylindrical member of said covering member, the slot being formed through the disc member.

10. A combination as claimed in Claim 9, further comprising a spring disposed inside the cylindrical member to urge the disc member into frictional engagement with a wall of the groove so that rotative movement of the disc member within the annular groove of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. unnecessarily change the idling mixture which has been appropriately set in consideration of the control of noxious gas emission during idling of the engine. However, the idling mixture may be changed and adjusted when necessary by turning the adjustment screw with the particularly designed adjusting tool which is provided, for example, in service stations. WHAT WE CLAIM IS:

1. A combination comprising: an idling mixture adjustment screw turnably and operatively installed in a carburetor of an internal combustion engine, for adjusting an air-fuel mixture supplied to the engine during idling of the engine when turned, said adjustment screw being formed with a head having first means engageable by a turning tool; a turning tool for turning the head of said adjustment screw, said turning tool being formed with an end portion having second means which is engageable with the first means of said adjustment screw to turn said adjustment screw after the second means engages with the first means; and a covering member for covering the head of said idling adjustment screw, said covering member having a slot formed through the wall of said covering member, said slot being generally in the shape which is produced by projecting the maximum cross-section of said second means of said turning tool on the surface of said covering member, so that the second means is just capable of passing through the slot to reach and engage the means.

cylindrical member is inhibited.

11. A combination as claimed in Claim 9, in which the head of said idling adjustment screw is formed, at its top surface, with a conical portion.

12. A combination as claimed in Claim 11, in which the first means of said idling adjustment screw includes two straight grooves formed on the surface of the conical portion of the head, each of two straight grooves extending from the vertex of the conical portion to the periphery of the head, the second means of said turning tool including a bifurcated plate member of which two plate portions are respectively engageable with the two straight grooves of the conical portion of said adjustment screw.

13. A combination as claimed in Claim 11, in which the first means of said idling adjustment screw includes four straight grooves formed on the surface of the conical portion of the head, each of the four straight grooves extending from the vertex of the conical portion to the periphery of the head, the second means of said turning tool including four finger-like members which are respectively engageable with the four straight grooves of the conical portion of said idling adjustment screw.

14. A combination as claimed in Claim 11, in which said first means of said idling adjustment screw includes two straight elongate projections formed on the surface of the conical portion, each of the projections extending from the vertex of the conical portion to the periphery of the head.

15. A combination as claimed in Claim 9, in which the top surface of the head of said idling adjustment screw is formed flat, the first means including two opposite grooves formed on the flat top surface of the head, each of two opposite grooves extending from the central portion of the flat top surface to the periphery of the head, and the second means including a bifurcated plate member of which two portions are respectively engageable with the two opposite grooves.

16. A combination as claimed in Claim 1, in which said idling adjustment screw is movably disposed in a passageway connecting the upstream and downstream sides of the venturi portion of a variable-venturi carburetor in which the cross-sectional area of the venturi portion is variable in response to the vacuum of intake air inducted to the engine, the idling adjustment screw being arranged to control the cross-sectional area of the passageway in order to control the amount of air supplied from the upstream side to the downstream side of the venturi portion.

17. A combination as claimed in Claim 16, further comprising means for fastening a cylindrical member to the body of the carburetor, the head of said idling adjustment screw being movable within the cylindrical member.

18. A combination as claimed in Claim 17, further comprising a spring disposed between the head of said adjustment screw and a disc member of said covering member to urge the disc member in the direction to separate from the head of said adjustment screw.

19. A combination constructed and arranged substantially as described herein with reference to the accompanying drawings.

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