Abstract:
An apparatus for adjusting the air-fuel ratio of a fuel mixture to be supplied to an engine. The apparatus has a pair of needle valve bodies and a pair of receptacles formed in a main body of a carburetor for receiving the needle valve bodies. Each needle valve body has a needle and a head. The needles are axially movable relative to a respective needle orifice. The needles may be axially advanced and retracted by rotating the needle valve bodies within the receptacles to respectively decrease and increase the flow of the fuel mixture around the needles and through the orifices. To prevent tampering with the needle valve body setting, the head of the needle valve body has an unconventional shape requiring a specialized tool to rotatably adjust the needle valve body. To further prevent tampering, the head is recessed with the main body of the carburetor. A retainer is disposed in the main body of the carburetor and receives the needle valve bodies to facilitate maintaining alignment of the needle valve bodies relative to the receptacles. The retainer assures that a constant fuel calibration setting is maintained through the orifices by resisting displacement of the needles due to such factors as external forces applied to the head of the needle valve body or engine vibration.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a Continuation-In-Part of U.S. patent application Ser. No. 10/341,648, filed Jan. 14, 2003, which claims the benefit of U.S. Provisional Application No. 60/395,030, filed Jul. 11, 2002. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to a carburetor fuel mixture adjustment assembly for adjusting the air-fuel ratio of a fuel mixture to be supplied to an engine.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known for a carburetor air-fuel mixture adjustment assembly to include a needle valve body that is threaded into a bore in a carburetor main body. The bore in such an assembly intersects a fuel passage in the carburetor main body. The needle valve body has a shank with a tip, a head and an exteriorly threaded portion between them received in a complementary threaded portion of the bore. The tip of the valve body is positioned in axial alignment with an annular seat or orifice of the fuel passage and can be axially advanced and retracted by rotation of the needle valve body within the receptacle to adjust the air-fuel ratio of a fuel mixture. Axial advancement and retraction of the tip relative to the seat or orifice respectively decreases and increases the cross-sectional area of the flow path through the seat or orifice to decrease and increase the amount of fuel that can flow through the orifice. The needle valve body is rotated by using a tool such as a screwdriver to engage a screw head of the valve body that protrudes from the carburetor main body. In some such assemblies, to prevent inadvertent or uncommanded rotation of the valve body within the bore, a tamper-resistant cap is placed over the screw head and is secured to, or braced against an adjacent structure.  
         [0004]     Fuel mixture adjustment assemblies of this type have “slop” or clearance between the respective threaded portions of the needle valve body and the bore which permits some axial and/or radial movement of the tip within the seat or orifice, such as when force is applied to the valve body head or while encountering engine vibration. This axial and/or radial movement can change the shape and size of the effective flow area around the tip enough to result in fuel flow rate changes of up to 20% from an optimum fuel flow rate as determined by the manufacturer. Fuel flow rate changes caused by needle “slop” can result in excessively rich or lean fuel mixtures that undesirably increase exhaust emissions and/or adversely affect engine performance. Therefore, it is desirable to reduce fuel flow fluctuations through the seat or orifice and the resulting affects on exhaust emissions and engine performance by limiting needle slop.  
         [0005]     To assist in reducing fuel flow fluctuations, it is known to incorporate a spring between the protruding head of the needle valve body and the main body of the carburetor. This creates an axial preload between the mating threads of the needle valve body and the receptacle, thereby reducing the amount of radial and/or axial deflection of the needle valve body within the receptacle and inhibits unintended rotation of the needle valve body.  
         [0006]     Another example of a stabilizing system for an air-fuel mixture adjustment needle valve is disclosed in Japanese Patent Application No. 7-346529 filed 12 Dec. 1995 (Japanese Laid-open Publication No. 9-158783 published 17 Jun., 1997). The Japanese Patent Application discloses a carburetor air-fuel mixture adjustment assembly as described above and including a pressure plate made of an elastic material and overlaid on an outer surface of the carburetor main body. The pressure plate includes an aperture that a threaded protruding portion of the needle valve body must be inserted through during assembly. The presence of the pressure plate limits movement of the needle valve body within the receptacle by holding the needle valve body in a centered position.  
         [0007]     The carburetor air-fuel mixture adjustment assembly disclosed in this Japanese Patent Application also includes an annular sealing member coaxially disposed between the shank portion of the needle valve body and the receptacle such that the sealing member is compressed between the receptacle and the shank to prevent air from passing between the receptacle and valve body and leaking into the fuel passage. The sealing member is essentially an elongated tube of constant inner and outer diameter that must be forced over a shank portion of the needle valve body then forced into a section of the receptacle shaped to receive the sealing member during assembly. To produce an effective seal against air leakage into the carburetor, machining tolerances must be tight for inner and outer circumferential surfaces of the sealing member, an outer circumferential surface of the shank portion of the valve body, and an inner circumferential surface of the portion of the receptacle receiving the sealing member.  
       SUMMARY OF THE INVENTION  
       [0008]     An apparatus for adjusting the air-fuel ratio of a carburetor with a needle valve body received in a receptacle of the carburetor body and having a seal between them preferably adjacent the tip and a retainer between them preferably adjacent the head of the needle valve body. The receptacle intersects a fuel passage in the carburetor main body. The needle valve body has a shank with a threaded portion between the tip and the head and is engaged with a complementary threaded portion in the receptacle so that rotation of the needle valve body axially advances and retracts the tip relative to a seat or orifice to respectively decrease and increase the flow area of the orifice through which fuel may pass. To prevent tampering with a factory setting of the needle valve body, preferably its head, may be received in a recess in the main body of the carburetor. Additionally, its head may have an unconventional, non-circular shape, thus requiring a specialized tool to rotatably adjust the needle valve body.  
         [0009]     Preferably, a generally annular seal is concentrically disposed on the shank of the needle valve body adjacent the tip and is compressed between the receptacle and the shank. A generally annular retainer is preferably disposed concentrically on the shank adjacent the head of the needle valve body and is compressed between the receptacle and the shank. The retainer laterally biases the threaded portion of the needle valve body into engagement with an interiorly threaded portion of the receptacle and ensures alignment of the intermediate portion of the needle valve body with the receptacle, thus inhibiting radial or lateral movement of the needle valve body within the receptacle. The retainer also inhibits unintended rotation of the needle valve body. The retainer assures that a constant fuel calibration setting is maintained through the orifice by resisting axial and radial needle displacement and rotation due to such factors as external forces applied to the head of the needle valve body or engine vibration.  
         [0010]     Another aspect of the invention provides an apparatus for adjusting the air-fuel ratio of a fuel mixture to be supplied to an engine having a main body with a retainer seat and a pair of fuel passages in communication with a pair of needle orifices. The main body has a pair of receptacles each having an interiorly threaded portion, with the receptacles communicating with a separate one of the fuel passages. A pair of needle valve bodies are received within a separate one of the receptacles, with each needle valve body including a tip, a head, an exteriorly threaded portion having a major diameter sized for complementary threaded engagement with the interiorly threaded portions of the receptacles, and an intermediate portion between the threaded portion and the head. A retainer has a pair of openings having diameters sized for a friction fit with a separate one of the intermediate portions to maintain a desired position of the needle valve bodies by inhibiting displacement of the tips relative to the needle orifices.  
         [0011]     Objects, features and advantages of the invention include providing an assembly that maintains a fuel calibration setting in use by resisting inadvertent or unintended needle displacement between the needle valve body and the receptacle, permits use of a shorter length, reduced mass, and less expensive needle valve body, reduces the effects of vibration of the needle valve body, prevents inadvertent adjustment of the needle valve body, provides additional sealing between the needle valve body and receptacle to maintain the proper air-fuel ratio of the fuel mixture, reduces the complexity of the machining required to manufacture the needle valve body and the cost to manufacture the needle valve body, reduces offset or eccentricity between the needle valve body and the receptacle, and improves the ease and efficiency of manufacturing and assembly of a carburetor air-fuel mixture adjustment assembly. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     These and other objects, features and advantages of this invention will become apparent from the following detailed description of the preferred embodiments and best mode, appended claims, and accompanying drawings in which:  
         [0013]      FIG. 1  is a perspective view of a carburetor including a fuel mixture adjustment assembly constructed according to a currently preferred embodiment of the invention;  
         [0014]      FIG. 2  is a fragmentary cross-sectional side view of the carburetor and assembly of  FIG. 1 ;  
         [0015]      FIG. 3  is a side view of a needle valve body of the assembly of  FIG. 1 ;  
         [0016]      FIG. 4  is an end view of the needle valve body of  FIG. 3 ;  
         [0017]      FIG. 5  is an end view of a sealing member of the assembly of  FIG. 1 ;  
         [0018]      FIG. 6  is a cross-sectional side view of the sealing member of  FIG. 5  taken along line  6 - 6  of  FIG. 5 ;  
         [0019]      FIG. 7  is a partial cross-sectional side view of a specialized tool used for adjusting the needle valve body;  
         [0020]      FIG. 8  is an end view of a head of the tool of  FIG. 7  looking in the direction of arrows  8 - 8  of  FIG. 7 ;  
         [0021]      FIG. 9  is a fragmentary cross-sectional view of a carburetor including a fuel mixture adjustment assembly constructed according to another currently preferred embodiment of the invention;  
         [0022]      FIG. 10  is an enlarged end view looking generally in the direction of arrow  10  in  FIG. 9  with a pair of needle valve bodies of  FIG. 9  removed;  
         [0023]      FIG. 11  is a fragmentary cross-sectional side view of one of the needle valve bodies being inserted in a receptacle of the carburetor of  FIG. 9 ;  
         [0024]      FIG. 11A  is an enlarged fragmentary cross-sectional side view of one of the needle valve bodies initially engaging a retainer of the fuel mixture adjustment assembly of  FIG. 9 ;  
         [0025]      FIG. 12  is an enlarged plan view of the retainer of the fuel mixture adjustment assembly of  FIG. 9  shown prior to inserting the needle valve bodies therein; and  
         [0026]      FIG. 13  is an enlarged partial cross-sectional view of the encircled area in  FIG. 11 . 
     
    
     DETAILED DESCRIPTION  
       [0027]      FIGS. 1 and 2  illustrate an apparatus  10  embodying this invention for adjusting the air-fuel ratio of a fuel mixture supplied by a carburetor  11 . The apparatus  10  includes a receptacle  12  formed in a main body  14  of a carburetor and a needle valve body  18  having a tip  22  concentrically supported within the receptacle  12  so that in operation, the tip  22  is disposed in an axially aligned orientation relative to a seat or orifice  34 . The tip  22  can be axially advanced and retracted by rotating the needle valve body  18  within the receptacle  12 . This axial movement of the tip  22  relative to the orifice  34  changes the effective flow area of the orifice  34  to adjust the air-fuel ratio of the fuel mixture.  
         [0028]     Carburetor  11  may be a diaphragm carburetor, float bowl carburetor or other type of carburetor which utilizes a needle valve to adjust the air-fuel ratio of a fuel mixture supplied by the carburetor. The carburetor body  14  has a first fuel passage  16  and a second fuel passage  17  with the orifice  34  providing a flow path between the two passages  16 ,  17 . The receptacle  12  intersects the first fuel passage  16  so that the fuel mixture flows around the tip  22  and through the orifice  34  and into the second fuel passage  17 . The fuel mixture then flows from the second fuel passage  17  into an air and fuel mixing passage  19 .  
         [0029]     The carburetor body  14  has an extended boss  65  with a recess  66  opening into an end opposite the orifice  34 . The recess  66  transitions into a retainer seat  52  that is preferably necked down from the recess  66 . The receptacle  12  has an interiorly threaded portion  32  that is preferably necked down from the retainer seat  52 . A seal seat  25  is constructed between the interiorly threaded portion  32  and the orifice  34 .  
         [0030]     The needle valve body  18  has a shank  24  with an integral tip  22 , head  28  and threaded portion  20  between them which in assembly mates with complementary threads  32  of the receptacle  12 . An intermediate portion  26  is integrally disposed between the head  28  and the threaded portion  20  and adjacent to a flange  30  of the head  28  defines a shoulder  56 .  
         [0031]     At least a portion of the head  28  of the needle valve body  18  is non-circular and is shown here as being generally D-shaped. The head  28  has a flat surface  54  extending axially from an end of the needle valve body  18  to the flange  30 . The non-circular head  28  requires an unconventional tool  60  (not normally available to end users of the carburetor), as shown in  FIGS. 7 and 8  to engage the head  28  and rotatably adjust the needle valve body  18  within the receptacle  12 . The need for an unconventional specialized tool helps to ensure that the needle valve body  18  will not be adjusted by an end user from a factory setting required to comply with environmental standards and restrictions as may be governmentally mandated and/or to avoid adverse or deleterious engine operation.  
         [0032]     As shown in  FIGS. 7 and 8 , the specialized tool  60  for engaging the generally D-shaped head  28  has an engagement socket  62  with an outside diameter sized to fit within the recess  66  and a receptacle portion  64  of the socket  62  having a generally D-shaped cavity that is complementary to and slightly larger than the head  28 . This permits the socket  62  to fit over the head  28  for engaging and rotating the head  28  to adjust the needle valve body  18  to the desired setting.  
         [0033]     To further inhibit adjustment of the needle valve body  18  from the preferred factory setting beyond the protection provided by the generally D-shape of the non-circular head  28 , in assembly, the head  28  is preferably wholly received within the recess  66  of the main body  14 . The recess  66  has an internal diameter and an axial depth sized to prevent readily available tools (such as a needle nose pliers) from engaging the head  28  of the needle valve body  28 , thereby making it difficult for anyone not having the specialized tool  60  from tampering with or changing the factory setting of the needle valve body  18 . By preventing tampering with the setting of the needle valve body  18  in this manner, no additional components may be required to prevent tampering. The prevention of tampering with the needle valve body  18  setting helps to ensure that the carburetor remains in compliance with the emissions standards that may be established by the EPA or other governmental organizations/agencies and/or the desired factory setting for proper operation of the engine.  
         [0034]     An annular seal  36  is concentrically disposed on the shank  24  of the needle valve body  18 . The seal  36 , best shown in  FIGS. 5 and 6 , is compressed between the receptacle  12  and the shank  24  of the needle valve body  18 . This stabilizes the tip  22  relative to the needle orifice  34  and prevents ambient air from passing between the needle valve body  18  and the receptacle  12  and entering the fuel passage  17 . Therefore, the seal  36  helps to maintain the desired air-fuel ratio of the fuel mixture to both improve the running performance of the engine and decrease exhaust emissions.  
         [0035]     The seal  36  has a generally frustroconical shape that includes integrally formed annular expansion and compression regions  38 ,  40 . The expansion and compression regions  38 ,  40  are disposed adjacent respective axially opposite ends of the sealing member  36  and are configured to engage the needle valve body  18  and the receptacle  12 , respectively. The expansion and compression regions  38 ,  40  are configured to provide a seal between the needle valve body  18  and the receptacle  12  without requiring close machining tolerances on interfacing surfaces of the needle valve body  18 , the receptacle  12  or the seal  36 . The expansion and compression regions  38 ,  40  are also configured to compensate for any misalignment or eccentricity that might exist between the shank  24  of the needle valve body  18  and the receptacle  12 . Thus, an effective seal between the needle valve body  18  and the receptacle  12  is maintained by the expansion and compression regions  38 ,  40  even when the needle valve body  18  is not concentrically disposed within the receptacle  12 .  
         [0036]     As best shown in  FIG. 6 , the expansion region  38  of the seal  36  is disposed at an axial inner end of the seal  36 . The expansion region  38  has a circumferential inner contact area  42  that is configured to expand slightly in a radially outward direction when installed over and around the shank  24  of the needle valve body  18 .  
         [0037]     The compression region  40  is disposed at an axial outer end of the seal  36  opposite the inner end. The compression region  40  has a circumferential outer contact area  44  that is configured to compress radially inward when seated in the receptacle  12 . The outer contact area  44  is preferably greater than the inner contact area  42  of the expansion region  38 . This ensures that the seal  36  stays in place when the shank  24  of the needle valve body  18  is backed out of the receptacle  12 . The amount of interference between the shank  24  and the expansion region  38  of the seal  36  is calibrated to prevent excessive drag on the shank  24  of the needle valve body  18 . The seal  36  is preferably formed of a thermoplastic polymer such as acetyl, but may be made of any suitable material such as, for example, rubber or metal.  
         [0038]     An annular retainer  46 , represented here as an o-ring, is concentrically disposed about the needle valve body  18  between the intermediate portion  26  and the retainer seat  52 . Preferably, the o-ring retainer  46  is disposed around the intermediate portion  26  so that in assembly, an interference or friction fit between the retainer  46  and the intermediate portion  26  causes an inner circumferential contact area  48  to expand slightly. In assembly, the threaded portion  20  and the shoulder defined by the flange  30  of the head  28  act to maintain the retainer  46  on the intermediate portion  26  of the needle valve body  18 .  
         [0039]     The retainer  46  has an outer circumferential contact area  50  that is configured to compress slightly when the retainer  46  is seated within the retainer seat  52 . Therefore, the retainer  46  is compressed radially between the intermediate portion  26  of the needle valve body  18  and the retainer seat  52 . The retainer seat  52  preferably has a diameter that is larger than the interiorly threaded portion  32 . The retainer  46 , while in compression between the intermediate portion  26  of the needle valve body  18  and the retainer seat  52  of the receptacle  12 , acts to bias the threaded portion  20  of the needle valve body  18  into frictional engagement with the threaded portion  32  of the receptacle  12 . The frictional engagement of the retainer  46  and the mating threads  20 ,  32  inhibits misalignment of the needle valve body  18  within the receptacle  12 , and thus, facilitates maintaining the desired fuel-air ratio and fuel mixture flow around the needle  22  and through the needle orifice  34 . In addition, the frictional engagement between the retainer  46  and the mating threads  20 ,  32  inhibits the inadvertent rotation or adjustment of the needle valve body  18  within the receptacle  12  due to such factors as, for example, engine vibration. It should be recognized that the retainer  46  fosters a reduction in the mass of the needle valve body  18  as shown in a preferred embodiment by effectively reducing its length. Additionally, the embodiment shown does not require a spring to establish a preload between the needle valve body  18  and the receptacle  12 .  
         [0040]     Additionally, to provide additional sealing to prevent ambient air from leaking past the threads of the needle valve body  18  and into the fuel passage  17  which would thereby affect the desired air-fuel ratio of the fuel mixture, the retainer  46  establishes an interference or compression fit between the intermediate portion  26  of the needle valve body  18  and the retainer seat  52  of the receptacle  12 . To accomplish this, the inner and outer circumferential contact areas  48 ,  50  have an interference or compression fit with the intermediate portion  26  and the retainer seat  52 , respectively. The retainer  46  is preferably formed of a thermoplastic polymer such as acetyl, but may be made of any suitable material such as, for example, plastic polymers, elastomers, thermoset polymers, rubbers or metals.  
         [0041]     In  FIGS. 9-13 , another presently preferred embodiment of this invention is shown wherein similar reference numerals offset by 100 are used to identify similar features as in the previous embodiment.  FIG. 9  illustrates an apparatus  110  embodying this invention for adjusting the air-fuel ratio of a fuel mixture supplied by a carburetor  111 . The apparatus  110  includes a pair of receptacles  112  formed in a main body  114  of the carburetor  111  and a pair of needle valve bodies  118  having needles or tips  122  concentrically supported within the receptacles  112  so that in operation, the tips  122  are disposed in an axially aligned orientation relative to a pair of seats or orifices  134 . The tips  122  can be axially advanced and retracted by rotating the needle valve bodies  118  within the receptacles  112 . This axial movement of the tips  122  relative to the orifices  134  changes the effective flow area of the orifices  134  to adjust the air-fuel ratio of the fuel mixture. The needle valve bodies  118  preferably can be adjusted independently of one another, as desired.  
         [0042]     Referring to  FIG. 11 , the carburetor body  114  has a pair of first fuel passages  116  and a pair of second fuel passages  117  with the orifices  134  providing flow paths between the pairs of passages  116 ,  117 . The receptacles  112  intersect the first fuel passages  116  so that the fuel mixture flows around the tips  122  and through the orifices  134  and into the second fuel passages  117 . The fuel mixture then flows from the second fuel passages  117  into an air and fuel mixing passage  119 .  
         [0043]     The carburetor body  114  preferably has an extended boss  165  with a recess  166  extending to base or first shoulder  143 . A first counterbore  147  extends axially inward from the first shoulder  143  to a second shoulder  167 , and a second counter bore or retainer seat  152  extends axially inward from the second shoulder  167  toward the receptacles  112 . The receptacles  112  have a pair of interiorly threaded portions  132  that are preferably reduced in diameter or necked down from the retainer seat  152 . As best shown in  FIG. 13 , a pair of seal or guide bushing seats  125  are constructed between the interiorly threaded portions  132  and the orifices  134 . The guide bushing seats  125  are preferably reduced in diameter from the threaded portions  132 , thereby presenting seat shoulders  133  between the threaded portions  132  and the seats  125 .  
         [0044]     In this embodiment, the pair of needle valve bodies  118  preferably are generally identical in construction, and so only one needle valve body is described in detail hereafter, unless otherwise specified. The needle valve body  118  has a shank  124  extending generally axially from the tip  122 , a head  128  and an exteriorly threaded portion  120  between the tip  122  and the head  128 . The threaded portion  120  has an initial thread  123  generally adjacent the shank  124  and a major diameter (A) sized for complementary threaded engagement with one of the interiorly threaded portions  132  of the receptacles  112 .  
         [0045]     The needle valve body  118  has an intermediate portion  126  integrally disposed between the head  128  and the threaded portion  120 . The intermediate portion  126  has a diameter greater than the major diameter (A) of the threaded portion  120 , and desirably has an externally threaded portion  127  with a major diameter (B) and minor diameter (B′). The threaded portion  127  has an initial thread  129  generally adjacent the threaded portion  120 , wherein the initial thread  129  is desirably located axially a predetermined distance (X) ( FIG. 13 ) from the initial thread  123 .  
         [0046]     The head  128  of the needle valve body  118  is preferably wholly received within the recess  166  of the main body  114  and may be constructed as described in the previous embodiment, and thus, is not discussed in further detail hereafter.  
         [0047]     A pair of annular seals or guide bushings  136  are concentrically disposed on the separate shanks  124  of the needle valve bodies  118 . The guide bushings  136  are preferably compressed between the guide bushing seats  125  and the shanks  124  of the needle valve bodies  118 . The guide bushings  136  assist in stabilizing the respective tips  122  in their desired radial relation relative to the needle orifices  134 , and prevent ambient air from passing between the needle valve bodies  118  and the receptacles  112  and entering the fuel passages  117 . The guide bushings  136  also inhibit fuel from passing between the needle valve bodies  118  and the receptacles  112  and exiting the fuel passages  117 . Accordingly, the guide bushings  136  assist in maintaining the desired air-fuel ratio of the fuel mixture to both improve the running performance of the engine and decrease exhaust emissions.  
         [0048]     The guide bushings  136  preferably are generally identical in construction, and so only one guide bushing is described in detail hereafter, unless otherwise specified. As shown in  FIGS. 11 and 13 , the guide bushing  136  preferably has an inner contact area or bore  142  sized for a friction fit on the shank  124  and a circumferential outer contact area  144  sized for a friction fit in the guide bushing seat  125 . Therefore, the bore  142  is configured to expand slightly when disposed on the shank  124 , while the outer contact area  144  is configured to compress radially inward when seated in the bushing seat  125 . To ensure that the guide bushing  136  stays in place when the shank  124  of the needle valve body  118  is backed out of the receptacle  112 , preferably the amount of interference fit or magnitude of friction force between the shank  124  and the bore  142  of the guide bushing  136  is calibrated to prevent excessive drag between the shank  124  and the bushing  136 . Accordingly, the outer contact area  144  preferably has at least a slightly increased friction fit in the guide bushing seat  125  as compared to the friction fit of the inner contact area  142  on the shank  124 .  
         [0049]     To facilitate positioning the guide bushing  136  in its proper axial position within the guide bushing seat  125 , and as best shown in  FIG. 13 , the guide bushing  136  preferably has a flange  145  extending radially outwardly from the outer contact area  144  for abutting engagement with the shoulder  133 . As such, the extent to which the guide bushing  136  may be inserted within the seat  125  is limited by the engagement of the flange  145  with the shoulder  133 . The guide bushing  136  is preferably formed of a thermoplastic polymer such as acetyl, but may be made of any suitable material such as, for example, metal.  
         [0050]     A retainer  146  is preferably formed of a thermoplastic polymer such as acetyl, but may be made of any suitable material such as, for example, plastic polymers, elastomers, thermoset polymers, rubbers or metals. The retainer  146  has a pair of housings  155  ( FIG. 12 ) that each have an annular inner contact area or opening  148  with diameters (C) sized for a friction fit on the intermediate portions  126  of the needle valve bodies  118 . As such, the major diameters (B) on the intermediate portions  126  of the needle valve bodies  118  are desirably greater than the diameters (C), and preferably the minor diameters (B′) are equal to or greater than the diameters (C) prior to engaging the intermediate portions  126  with the openings  148 . The retainer  146  is constructed as a single piece of material such that the housings  155  are interconnected to one another by a medial connector  149 . The retainer  146  has an outer contact area or surface  150  that is preferably sized for a friction fit within the retainer seat  152 . The outer contact surface  150  preferably compresses slightly radially inward when the retainer  146  is seated within the retainer seat  152 . Desirably, to facilitate locating the retainer  146  axially within the retainer seat  152 , the retainer  146  has a flange  151  extending radially outwardly from the outer contact surface  150  presenting a surface  169  for abutting engagement with the second shoulder  167 . Further, to facilitate maintaining the retainer  146  in the retainer seat  152 , radially inwardly extending protrusions  173  are preferably formed in the first shoulder  143 , such as in a staking, crimping or peening operation, for example. The protrusions  173  are thus formed from the first shoulder material being plastically deformed generally radially inwardly into frictional engagement with the flange  151  on the retainer  146 .  
         [0051]     In assembly, guide bushings  136  may either be pressed with a friction fit into their respective guide bushing seats  125  until the flanges  145  engage the shoulders  133 , or the guide bushings  136  may be disposed on the shanks  124  of the needle valve bodies  118  for automatic installation of the guide bushings  136  upon insertion of the needle valve bodies  118  into their respective receptacles  112 .  
         [0052]     The retainer  146  is inserted within the recess  166  and pressed into the retainer seat  152  until the surface  169  of the flange  151  engages the second shoulder  167 . Though the friction fit between the outer surface  150  of the retainer  146  and the retainer seat  152  assists in maintaining the retainer  146  in its intended position, preferably the protrusions  173  are formed in the first shoulder  143 , such as through a staking operation, for example, to ensure that the retainer  146  is maintained in its desired position.  
         [0053]     With the retainer  146  assembled in the retainer seat  152 , the needle valve bodies  118  are inserted into their respective receptacles  112 . As the needle valve bodies are being inserted into the receptacles  112 , the initial threads  123  on the threaded portions  120  preferably engage the internally threaded portions  132  in the carburetor body  114  prior to the initial threads  129  of the intermediate portions  126  engaging the openings  148  within the retainer  146 . This acts to avoid complications, such as cross threading, for example, between the threaded portions  120  of the needle valve bodies  146  and the threaded portions  132  in the carburetor body  114 , which may otherwise result if the threaded portions  127  were allowed to engage the retainer  146  prior to the threaded portions  120  engaging the carburetor body  114 . This desired result is due to the spacing (X) between the initial threads  123 ,  129 .  
         [0054]     As the threaded intermediate portions  126  threadingly engage the openings  148  in the retainer  146  ( FIG. 11A ), the threaded portions  127  form self tapped threads  175  in the openings  148 . This results from the major diameters (B) or minor diameters (B′) being greater than the diameters (C).  
         [0055]     The retainer  146 , while in compression between the intermediate portions  126  of the needle valve bodies  118  and the retainer seats  152  of the receptacles  112 , acts to inhibit misalignment of the needle valve bodies  118  within the receptacles  112 , and thus, facilitates maintaining the desired fuel-air ratio and fuel mixture flow around the tips  122  and through the needle orifices  134 . In addition, the friction force created by the engagement between the retainer  146  and the mating threaded portions  127  inhibits the inadvertent rotation or adjustment of the needle valve bodies  118  within the receptacles  112 , which tends to result from such factors as engine vibration, for example. As such, the retainer  146  eliminates the need for other anti-rotation devices, such as a spring to establish a preload between the needle valve body  118  and the receptacle  112 , for example. Further, the retainer  146  provides added sealing between the needle valve body  118  and the receptacle  112  in addition to the sealing provided by the guide bushing  136 , thus, further preventing ambient air from leaking past the threaded portions  127  of the needle valve bodies  118  and into the fuel passages  117 , as described in the previous embodiment.  
         [0056]     This description is intended to illustrate certain currently preferred embodiments of the invention rather than to limit the invention. Therefore, it uses descriptive rather than limiting words. Obviously, it is possible to modify this invention from what the description describes and shows. For example, it should be recognized that though the head  28  of the needle valve body  18  is shown as being D-shaped, other unconventional configurations may be used to prevent standard tools available to retail consumers from being used to adjust the needle valve body. As another example, seals or retainers of different sizes, shapes, and arrangements may be used without departing from the spirit and scope of the invention as defined in the following claims. Within the scope of the claims, one may practice the invention other than as described.