Abstract:
A carburetor includes a body having an inner wall and an air/fuel passageway. An insert includes a base having a shape that closely matches the inner wall and a first tower having a first end disposed within the air/fuel passageway. A main circuit passageway is at least partially formed within the first tower and has a first end in fluid communication with the air/fuel passageway and a second end in fluid communication with the fuel bowl chamber. The main circuit passageway carries fuel from the fuel bowl chamber to the air/fuel passageway during engine operation when the throttle valve is opened. A second tower has a first end coupled to the base and a second end spaced away from the base. The first end of the first tower, the second end of the second tower, and the base are the sole engagement points between the insert and the body.

Description:
RELATED APPLICATION DATA 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 12/719,103 filed Mar. 8, 2010, now U.S. Pat. No. ______. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to internal combustion engines, and more particularly to carburetors for use with internal combustion engines. Small engines for use with, for example, outdoor power equipment (e.g., walk-behind mowers, etc.) typically utilize carburetors for supplying a mixture of air and fuel to the engine. Such carburetors typically include die-cast metal bodies and many small parts that are assembled to the body. Many machining processes are also often employed on the die-cast metal bodies in preparation for final assembly. 
         [0003]    Other carburetors, however, include bodies that are molded from a plastic material. Such molded plastic carburetor bodies often include one or more apertures or passageways formed therein which otherwise would be machined in an equivalent die-cast metal carburetor body. However, such molded plastic carburetor bodies typically require some machining in preparation for final assembly of the carburetor. For example, it is common to employ one or more drilling processes in conventional molded plastic carburetor bodies to form connecting passageways between two or more molded passageways. Subsequent manufacturing processes, such as plugging a portion of the drilled passageway and welding the plug to the carburetor body, are also commonly employed in manufacturing carburetors having molded plastic bodies. 
       SUMMARY 
       [0004]    The present invention provides, in one aspect, a carburetor for use with an internal combustion engine. The carburetor includes a body having an air/fuel passageway and a fuel passageway formed therein, a throttle valve positioned in the air/fuel passageway, a fuel bowl coupled to the body, a fuel bowl chamber at least partially defined by the fuel bowl, and a one-piece fuel-metering insert coupled to the body. The insert includes an idle circuit passageway having a first end in fluid communication with the fuel passageway and a second end in fluid communication with the fuel bowl chamber. The idle circuit passageway is configured to carry fuel from the fuel bowl chamber to the air/fuel passageway via the fuel passageway during engine operation when the throttle valve is oriented in a substantially closed position. The insert also includes a main circuit passageway having a first end in fluid communication with the air/fuel passageway and a second end in fluid communication with the fuel bowl chamber. The main circuit passageway is configured to carry fuel from the fuel bowl chamber to the air/fuel passageway during engine operation when the throttle valve is opened from the substantially closed position. 
         [0005]    In another construction, the invention provides a carburetor for use with an internal combustion engine. The carburetor includes a body including an air/fuel passageway formed therein, a stem formed as part of the body and defining an inner wall, and a throttle valve positioned in the air/fuel passageway. The carburetor also includes a fuel bowl coupled to the body, a fuel bowl chamber at least partially defined by the fuel bowl, and a fuel-metering insert formed as a separate piece from the body and coupled to the body. The insert includes a base having an outer surface having a shape that closely matches the shape of the inner wall and a first tower having a first end disposed within the air/fuel passageway and a second end coupled to the base. A main circuit passageway is at least partially formed within the first tower and has a first end in fluid communication with the air/fuel passageway and a second end in fluid communication with the fuel bowl chamber. The main circuit passageway is configured to carry fuel from the fuel bowl chamber to the air/fuel passageway during engine operation when the throttle valve is opened from the substantially closed position. A second tower has a first end coupled to the base and a second end spaced away from the base. The first end of the first tower, the second end of the second tower, and the base are the sole engagement points between the insert and the body. 
         [0006]    In yet another construction, the invention provides a carburetor for use with an internal combustion engine. The carburetor includes a body including an air/fuel passageway, a first receptacle and a second receptacle, a stem formed as part of the body and defining a space having a first perimeter, and a throttle valve positioned in the air/fuel passageway. The carburetor also includes a fuel bowl coupled to the body, a fuel bowl chamber at least partially defined by the fuel bowl, and a fuel-metering insert including a base having a second perimeter, a first tower extending from the base in a first direction and a second tower extending from the base in the first direction. The fuel-metering insert is insertable into the stem such that the first tower is sealingly received within the first receptacle, the second tower is received within the second receptacle, and the first perimeter and the second perimeter engage one another to define a seal therebetween. A main circuit passageway is at least partially formed within the first tower and has a first end in fluid communication with the air/fuel passageway and a second end in fluid communication with the fuel bowl chamber. The main circuit passageway is configured to carry fuel from the fuel bowl chamber to the air/fuel passageway during engine operation when the throttle valve is opened from the substantially closed position. 
         [0007]    Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a first end of a first construction of a carburetor according to the invention, illustrating an air/fuel passageway and a choke valve in the air/fuel passageway. 
           [0009]      FIG. 2  is a perspective view of a second end of the carburetor of  FIG. 1 , illustrating a throttle valve in the air/fuel passageway. 
           [0010]      FIG. 3  is an exploded, bottom perspective view of the carburetor of  FIG. 1 , illustrating a one-piece fuel-metering insert. 
           [0011]      FIG. 4  is a front perspective view of the fuel-metering insert of  FIG. 3 . 
           [0012]      FIG. 5  is an assembled, side view of the carburetor of  FIG. 1 . 
           [0013]      FIG. 6  is an assembled, top view of the carburetor of  FIG. 1 . 
           [0014]      FIG. 7  is a cross-sectional view of the carburetor of  FIG. 1  taken along line  7 - 7  in  FIG. 5 . 
           [0015]      FIG. 8  is a cross-sectional view of the carburetor of  FIG. 1  taken along line  8 - 8  in  FIG. 6 . 
           [0016]      FIG. 9  is a cross-sectional view of the carburetor of  FIG. 1  taken along line  9 - 9  in  FIG. 6 . 
           [0017]      FIG. 10  is a cross-sectional view of the carburetor of  FIG. 1  taken along line  10 - 10  in  FIG. 6 . 
           [0018]      FIG. 11  is a cross-sectional view of the carburetor of  FIG. 1  taken along line  11 - 11  in  FIG. 6 . 
           [0019]      FIG. 12  is a perspective view of a first end of a second construction of a carburetor according to the invention, illustrating an air/fuel passageway and a choke valve in the air/fuel passageway. 
           [0020]      FIG. 13  is a perspective view of a second end of the carburetor of  FIG. 12 , illustrating a throttle valve in the air/fuel passageway. 
           [0021]      FIG. 14  is an exploded, bottom perspective view of the carburetor of  FIG. 12 , illustrating a one-piece fuel-metering insert. 
           [0022]      FIG. 15  is a front perspective view of the fuel-metering insert of  FIG. 14 . 
           [0023]      FIG. 16  is an assembled, side view of the carburetor of  FIG. 12 . 
           [0024]      FIG. 17  is an assembled, top view of the carburetor of  FIG. 12 . 
           [0025]      FIG. 18  is a cross-sectional view of the carburetor of  FIG. 12  taken along line  18 - 18  in  FIG. 22 . 
           [0026]      FIG. 19  is a cross-sectional view of the carburetor of  FIG. 12  taken along line  19 - 19  in  FIG. 17 . 
           [0027]      FIG. 20  is a cross-sectional view of the carburetor of  FIG. 12  taken along line  20 - 20  in  FIG. 17 . 
           [0028]      FIG. 21  is a cross-sectional view of the carburetor of  FIG. 12  taken along line  21 - 21  in  FIG. 17 . 
           [0029]      FIG. 22  is a cross-sectional view of the carburetor of  FIG. 12  taken along line  22 - 22  in  FIG. 17 . 
       
    
    
       [0030]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
       DETAILED DESCRIPTION 
       [0031]      FIGS. 1 and 2  illustrate a first construction of a carburetor  10  configured for use with a small internal combustion engine. Such an engine may be utilized in outdoor power equipment (e.g., a lawnmower, snow thrower, etc.) or other types of engine-powered equipment (e.g., a generator). The carburetor  10  includes a body  14  defining an air/fuel passageway  18  in which a mixture of fuel and air is created for consumption by the engine. The body  14  is made of a single piece of plastic material using a molding process, with the exception of a few fittings or plugs coupled to the body  14  after it is molded. Alternatively, the body  14  may be made from metal as a single piece using a casting process. The carburetor  10  includes a choke valve  22  ( FIG. 1 ) positioned in an upstream portion  24  of the passageway  18 , and a throttle valve  26  ( FIG. 2 ) positioned in a downstream portion  28  of the passageway  18 . Movement of the choke valve  22  and throttle valve  26  may be controlled in a conventional manner using mechanical linkages (e.g., shafts, arms, cables, etc.). Alternatively, the choke valve  22  may be omitted. 
         [0032]    With reference to  FIG. 3 , the carburetor  10  also includes a fuel bowl  30  coupled to the body  14 . The body  14  and the fuel bowl  30  define a fuel bowl chamber  34  in which fuel is stored ( FIG. 8 ). The carburetor  10  also includes a float  38  pivotably coupled to the body  14  ( FIG. 3 ). The float  38  is operable in a conventional manner in conjunction with a valve (not shown) to meter the amount of fuel introduced into the fuel bowl chamber  34 . Alternatively, the carburetor  10  may include different structure, besides the float  38 , with which to meter the amount of fuel introduced into the fuel bowl chamber  34 . 
         [0033]    With reference to  FIGS. 3 and 4 , the carburetor  10  also includes a fuel-metering insert  42  coupled to a stem  46  on the body  14 . As shown in  FIG. 4 , the insert  42  includes a base  50 , an idle circuit conduit  54  extending from the base  50 , and a main circuit conduit  58  extending from the base  50 . In the illustrated construction of the carburetor  10 , the insert  42  is formed as a single piece of plastic material using a molding process. Alternatively, the insert  42  may be made from metal as a single piece using a casting process. With reference to  FIG. 10 , the idle circuit conduit  54  defines therein an idle circuit passageway  62  through which fuel flows from the fuel bowl chamber  34  to the air/fuel passageway  18  when the throttle valve  26  is oriented in a substantially closed position corresponding with an idle speed of the associated engine. The main circuit conduit  58  defines therein a main circuit passageway  66  through which fuel flows from the fuel bowl chamber  34  to the air/fuel passageway  18  when the throttle valve  26  is opened from its substantially closed position when the associated engine is operating at part throttle or full throttle. 
         [0034]    With continued reference to  FIG. 10 , the stem  46  extends into the fuel bowl chamber  34 , and the insert  42  is supported within the interior of the stem  46 . In the illustrated construction of the carburetor  10 , the insert  42  is coupled and secured to the stem  46  using a snap-fit. Specifically, the insert  42  includes a lip  70  formed around the outer periphery of the base  50 , and the stem  46  includes an interior wall  74  defining therein a groove  78  in which the lip  70  is received. As such, the insertion of the lip  70  into the groove  78  provides an indication (e.g., with an audible click) during assembly that the insert  42  is fully inserted within the stem  46 . The configuration of the lip  70  and the groove  78  also substantially prevents unintentional removal of the insert  42  from the stem  46 , effectively permanently securing the insert  42  to the carburetor body  14 . Alternatively, the lip  70  may be formed on the interior wall  74 , and the groove  78  may be formed in the outer periphery of the base  50  of the insert  42 . As a further alternative, the stem  46  and the insert  42  may utilize any of a number of different structural features or components with which to couple and secure the insert  42  to the stem  46 . Likewise, any of a number of different processes may be employed to couple and secure the insert  42  to the stem  46  (e.g., using an interference fit, using adhesives, welding, etc.). 
         [0035]    With continued reference to  FIG. 10 , the base  50  of the insert  42  includes a groove  82  in which a seal  86  (e.g., an O-ring) is positioned. The seal  86  is engaged with the interior wall  74  of the stem  46  about the inner periphery of the stem  46  to substantially prevent fuel from leaking between the insert  42  and the interior wall  74  of the stem  46 . In addition, the combination of the lip  70  and the groove  78  also functions as a seal to substantially prevent fuel from leaking between the insert  42  and the interior wall  74  of the stem  46 . Consequently, the stem  46  and the insert  42  at least partially define an air chamber  90 , located above the insert  42 , within the interior of the stem  46 . Specifically, the lower extent of the air chamber  90  is defined by an upper wall  94  of the base  50  from which the idle circuit conduit  54  and the main circuit conduit  58  extend. The main circuit conduit  58  includes a plurality of apertures  98  fluidly communicating the main circuit passageway  66  and the air chamber  90 , the function of which is described in more detail below. 
         [0036]    With continued reference to  FIG. 10 , the insert  42  includes a lower wall  102  spaced from the upper wall  94 , and a jet  106  supported by the lower wall  102 . The walls  94 ,  102  define therebetween a fuel reservoir  110 , and the jet  106  includes an orifice  114  sized to meter fuel flow from the fuel bowl chamber  34  to the fuel reservoir  110 . In the illustrated construction of the carburetor  10 , the jet  106  is configured as a separate and distinct component from the insert  42  that is coupled to the insert  42  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). Alternatively, the jet  106  may be omitted, and the lower wall  102  may include an orifice substantially identical to the orifice  114  in the jet  106  to meter fuel flow from the fuel bowl chamber  34  to the fuel reservoir  110 . 
         [0037]    Respective ends  118 ,  122  of the idle circuit passageway  62  and the main circuit passageway  66  are in fluid communication with the fuel reservoir  110  to draw fuel directly from the fuel  110  reservoir during operation of the engine incorporating the carburetor  10 . Another jet  126  is coupled to the idle circuit conduit  54  at a location proximate an opposite end  130  of the idle circuit passageway  62 . The jet  126  includes an orifice  134  sized to meter fuel flow that is discharged from or exiting the idle circuit passageway  62 . In the illustrated construction of the carburetor  10 , the jet  126  is configured as a separate and distinct component from the insert  42  that is coupled to the insert  42  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). Alternatively, the jet  126  may be omitted, and the end  130  of the idle circuit passageway  62  may be formed to include an orifice substantially identical to the orifice  134  in the jet  126  to meter fuel flow exiting the idle circuit passageway  62 . 
         [0038]    With continued reference to  FIG. 10 , the carburetor body  14  includes a receptacle  138  within the stem  46  into which the idle circuit conduit  54  is at least partially received. In the illustrated construction of the carburetor  10 , the receptacle  138  is at least partially defined by the interior wall  74  of the stem  46  and an arcuate wall  142  extending from the carburetor body  14  toward the fuel bowl  30 . Alternatively, the receptacle  138  may be defined by different structure of the carburetor body  14 . The idle circuit conduit  54  includes a groove  146  in which a seal  150  (e.g., an O-ring) is positioned. A portion of the seal  150  is engaged with the interior wall  74  of the stem  46 , and the remaining portion of the seal  150  is engaged with the arcuate wall  142  to substantially prevent fuel exiting the idle circuit passageway  62  from leaking between the idle circuit conduit  54 , the interior wall  74 , and the arcuate wall  142 . 
         [0039]    With continued reference to  FIG. 10 , the carburetor body  14  includes an aperture  154  through which the main circuit conduit  58  extends. As a result, an end  158  of the main circuit passageway  66  opposite the end  122  is disposed in the air/fuel passageway  18  and is in fluid communication with the air/fuel passageway  18 . Specifically, the portion of the main circuit conduit  58  protruding into the air/fuel passageway  18  is disposed proximate a venturi  162  in the carburetor  10  ( FIG. 7 ). As a result, the end  158  of the main circuit passageway  66  is disposed in a region of relatively low pressure in the air/fuel passageway  18 , thereby allowing fuel to be drawn from the fuel reservoir  110 , via the main circuit passageway  66 , and into the air/fuel passageway  18  during part-throttle or full-throttle engine operation. 
         [0040]    In the illustrated construction of the carburetor  10 , the venturi  162  is configured as a separate insert that is disposed in the air/fuel passageway  18 . The venturi  162  includes a lip  163  surrounding the inlet of the venturi  162  that is deflectable in response to engaging an adjacent interior wall  167  of the carburetor body  14 . The venturi  162  also includes an aperture  164  through which the main circuit conduit  58  extends. During insertion of the insert  42  into the stem  46 , the tapered end of the main circuit conduit  58  is received in the aperture  164  to facilitate locating the venturi  162  into its final position in the air/fuel passageway  18 . As the venturi  162  is brought into its final position, the lip  163  engages the adjacent interior wall  167  and at least partially deflects, thereby creating an interference fit between the venturi  162  and the adjacent interior wall  167  to seal the venturi  162  against the adjacent interior wall  167 . This, in turn, substantially prevents any leakage from occurring between the venturi  162  and the adjacent interior wall  167 . Another seal (e.g., an O-ring  165 ) is disposed about the outer periphery of the venturi  162  and is engaged with the adjacent interior wall to supplement the seal created between the lip  163  and the adjacent interior wall. The central orifice of the venturi  162  may have any of a number of different sizes depending upon the airflow requirements of the engine with which the carburetor  10  is used. 
         [0041]    With reference to  FIG. 8 , the carburetor body  14  includes a fuel passageway  166  defining a longitudinal axis  170 , and an idle circuit air bleed passageway  174 , defining a longitudinal axis  178  substantially parallel with the direction of the air/fuel passageway  18 , in fluid communication with the fuel passageway  18 . Specifically, the idle circuit air bleed passageway  174  includes an inlet  182  exposed to the upstream portion  24  of the air/fuel passageway  18 , and an outlet  186  exposed to a throttle progression pocket  190  formed in the carburetor body  14  (see also  FIG. 7 ). The fuel passageway  166  is in fluid communication with the idle circuit air bleed passageway  174  at a location between the inlet  182  and the outlet  186  of the idle circuit air bleed passageway  174 . The fuel passageway  166  is also in fluid communication with the idle circuit passageway  62  to receive fuel discharged from or exiting the idle circuit passageway  62  during operation of the engine. As is described in more detail below, the fuel passageway  166  introduces fuel into the idle circuit air bleed passageway  174 , and the resultant air/fuel mixture is delivered to the throttle progression pocket  190  for use by the engine during idle. In the illustrated construction of the carburetor  10 , the respective axes  170 ,  178  of the fuel passageway  166  and the idle circuit air bleed passageway  174  are oriented substantially normal or orthogonal to each other and are contained within a common plane (e.g., plane  8 - 8  in  FIG. 6 ). Such an arrangement of the respective passageways  166 ,  174  facilitates molding the carburetor body  14  as a single piece, with the passageways  166 ,  174  being formed during the molding process. As such, subsequent machining processes are not required to create either of the respective passageways  166 ,  174 . 
         [0042]    With reference to  FIGS. 7 and 8 , a plurality of apertures  194  fluidly communicate the throttle progression pocket  190  with the downstream portion  28  of the air/fuel passageway  18 . As is described in more detail below, the throttle valve  26  progressively uncovers the apertures  194  as the throttle valve  26  opens from its substantially closed position at idle to provide a smooth transition from the engine idling to part-throttle or full-throttle operation of the engine. As shown in  FIG. 7 , the carburetor  10  includes a plug  198  coupled to the body  14  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). The plug  198  at least partially defines the pocket  190 , and substantially prevents air from being drawn into the pocket  190  to dilute the air/fuel mixture in the pocket  190 . 
         [0043]    With reference to  FIGS. 9 and 10 , the carburetor body  14  includes a main circuit air bleed passageway  202  having an inlet  206  ( FIG. 9 ) exposed to the upstream portion  24  of the air/fuel passageway  18 , and an outlet  210  ( FIG. 10 ) exposed to the air chamber  90  in the interior of the stem  46 . In the illustrated construction of the carburetor  10 , the main circuit air bleed passageway  202  includes a first portion  214  having the inlet  206  at one end and defining a longitudinal axis  218  that is oriented horizontally relative to the point of view of  FIG. 9 . The main circuit air bleed passageway  202  also includes a second portion  222  having the outlet  210  at one end and defining a longitudinal axis  226  that is oriented horizontally relative to the point of view of  FIG. 10 . The main circuit air bleed passageway  202  further includes an intermediate, third portion  230  defining a longitudinal axis  234  that is oriented substantially vertically relative to the point of view of  FIGS. 9 and 10 . The third portion  230  of the main circuit air bleed passageway  202  fluidly communicates the first and second portions  214 ,  222 . In the illustrated construction of the carburetor  10 , the longitudinal axes  218 ,  226 ,  234  of the respective first, second, and third portions  214 ,  222 ,  230  of the main circuit air bleed passageway  202  are oriented mutually orthogonal to each other to facilitate molding the carburetor body  14  as a single piece, with the passageway  202  being formed during the molding process. As such, subsequent machining processes are not required to create any of the respective portions  214 ,  222 ,  230  of the passageway  202 . 
         [0044]    With reference to  FIG. 10 , a first plug  238  is at least partially positioned within the second portion  222  of the main circuit air bleed passageway  202  at a location disposed from the outlet  210 , and a second plug  242  is at least partially positioned within the third portion  230  of the main circuit air bleed passageway  202  at a location disposed from an end of the third portion  230  exposed to the second portion  222  of the main circuit air bleed passageway  202 . The respective plugs  238 ,  242  direct the flow of air from the inlet  206  to the outlet  210 , and substantially prevent leakage of air into the main circuit air bleed passageway  202  between the inlet  206  and the outlet  210 . In the illustrated construction of the carburetor  10 , each of the plugs  238 ,  242  is configured as a ball bearing that is press-fit or interference fit to the carburetor body  14 . Alternatively, the plugs  238 ,  242  may be differently configured, and the plugs  238 ,  242  may be secured to the carburetor body  14  in any of a number of different ways (e.g., by using adhesives, by welding, etc.). 
         [0045]    With reference to  FIGS. 1 and 11 , the carburetor body  14  also includes a priming passageway  246  in fluid communication with the fuel bowl chamber  34 . The priming passageway  246  includes an inlet  248  (see  FIG. 1 ) positioned in a flange of the body  14  configured for mounting to an air cleaner assembly (not shown) of the engine incorporating the carburetor  10 . The air cleaner assembly may include a primer bulb and another priming passageway, in which the primer bulb is at least partially disposed, in fluid communication with the inlet  248  of the priming passageway  246 . With reference to  FIG. 11 , the carburetor  10  includes a plug  250  positioned in the priming passageway  246 . Although not shown, the plug  250  may include a small aperture or orifice to provide external venting of the fuel bowl chamber  34 . The small aperture or orifice in the plug  250  may also be sized to tune the amount of primer charge that results when an operator of the engine depresses the primer bulb in the air cleaner assembly to prime the carburetor  10  prior to starting the engine. Specifically, an operator may depress the primer bulb to displace the air in the priming passageway  246  down into the fuel bowl chamber  34 , thereby displacing a substantially equivalent volume of fuel through the insert  42  (e.g., via the main circuit passageway  66 ) and into the air/fuel passageway  18  to enrichen the air/fuel mixture delivered to the engine during startup. 
         [0046]    In operation of the carburetor  10  during engine idling, the region of relatively low pressure downstream of the throttle valve  26 , when oriented in a substantially closed position, creates an airflow through the idle circuit air bleed passageway  174  which, in turn, draws fuel from the fuel bowl chamber  34 , through the orifice  114  in the jet  106 , and into the fuel reservoir  110  ( FIG. 10 ). Fuel is subsequently drawn from the fuel reservoir  110 , through the idle circuit passageway  62 , through the orifice  134  in the jet  126 , through the fuel passageway  166  in the carburetor body  14 , and into the idle circuit air bleed passageway  174 , where the fuel mixes with the air in the passageway  174 . With reference to  FIG. 8 , the air/fuel mixture in the idle circuit air bleed passageway  174  then moves into the throttle progression pocket  190 , where the air/fuel mixture may be drawn through one of the apertures  194  and into the air/fuel passageway  18  to maintain idling the engine. As the throttle valve  26  opens from its substantially closed position, more of the apertures  194  are uncovered to draw a progressively increasing amount of air/fuel mixture from the pocket  190 , thereby providing a smooth transition to part-throttle or full-throttle engine operation. 
         [0047]    During part-throttle or full-throttle engine operation, the region of relatively low pressure surrounding the portion of the main circuit conduit  58  protruding into the air/fuel passageway  18  creates an airflow through the main circuit air bleed passageway  202  and draws fuel from the fuel bowl chamber  34 , through the orifice  114  in the jet  106 , and into the fuel reservoir  110  ( FIG. 10 ). Fuel is subsequently drawn from the fuel reservoir  110  and through the main circuit passageway  66 , which causes air in the air chamber  90  to be drawn through the apertures  98  and into the main circuit passageway  66  to mix with the fuel in the main circuit passageway  66 . The resultant air/fuel mixture in the main circuit passageway  66  is discharged directly into the air/fuel passageway  18  for use by the engine during part-throttle or full-throttle operation. 
         [0048]      FIGS. 12 and 13  illustrate a second construction of a carburetor  310  configured for use with a small internal combustion engine. The carburetor  310  includes a body  314  defining an air/fuel passageway  318  in which a mixture of fuel and air is created for consumption by the engine. The body  314  is made of a single piece of plastic material using a molding process, with the exception of a few fittings or plugs coupled to the body  314  after it is molded. Alternatively, the body  314  may be made from metal as a single piece using a casting process. The carburetor  310  includes a choke valve  322  positioned in an upstream portion  324  of the passageway  318  ( FIG. 12 ), and a throttle valve  326  ( FIG. 13 ) positioned in a downstream portion  328  of the passageway  318 . Movement of the choke valve  322  and throttle valve  326  may be controlled in a conventional manner using mechanical linkages (e.g., shafts, arms, cables, etc.). Alternatively, the choke valve  322  may be omitted. 
         [0049]    With reference to  FIG. 14 , the carburetor  310  also includes a fuel bowl  330  coupled to the body  314 . The body  314  and the fuel bowl  330  define a fuel bowl chamber  334  in which fuel is stored ( FIG. 19 ). The carburetor  310  also includes a float  338  pivotably coupled to the body  314  ( FIG. 14 ). The float  338  is operable in a conventional manner in conjunction with a valve (not shown) to meter the amount of fuel introduced into the fuel bowl chamber  334 . Alternatively, the carburetor  310  may include different structure, besides the float  338 , with which to meter the amount of fuel introduced into the fuel bowl chamber  334 . 
         [0050]    With reference to  FIGS. 14 and 15 , the carburetor  310  also includes a fuel-metering insert  342  coupled to a stem  346  on the body  314 . As shown in  FIG. 15 , the insert  342  includes a base  350 , an idle circuit conduit  354  extending from the base  350 , a main circuit conduit  358  extending from the base  350 , and a projection  360  extending from the base  350 , the purpose of which is described in more detail below. In the illustrated construction of the carburetor  310 , the insert  342  is formed as a single piece of plastic material using a molding process. Alternatively, the insert  342  may be made from metal as a single piece using a casting process. With reference to  FIG. 21 , the idle circuit conduit  354  defines therein an idle circuit passageway  362  through which fuel flows from the fuel bowl chamber  334  to the air/fuel passageway  318  when the throttle valve  326  is oriented in a substantially closed position corresponding with an idle speed of the associated engine. The main circuit conduit  358  defines therein a main circuit passageway  366  through which fuel flows from the fuel bowl chamber  334  to the air/fuel passageway  318  when the throttle valve  326  is opened from its substantially closed position when the associated engine is operating at part throttle or full throttle. In other words, when the engine is operating at part throttle or full throttle, fuel is drawn into the air/fuel passageway  318  via the main circuit passageway  366 . 
         [0051]    With continued reference to  FIG. 21 , the stem  346  extends into the fuel bowl chamber  334 , and the insert  342  is supported within the interior of the stem  346 . In the illustrated construction of the carburetor  310 , the insert  342  is coupled and secured to the stem  346  using a snap-fit. Specifically, the insert  342  includes a lip  370  formed around the outer periphery of the base  350 , and the stem  346  includes an interior wall  374  defining therein a groove  378  in which the lip  370  is received. As such, the insertion of the lip  370  into the groove  378  provides an indication (e.g., with an audible click) during assembly that the insert  342  is fully inserted within the stem  346 . The configuration of the lip  370  and the groove  378  also substantially prevents unintentional removal of the insert  342  from the stem  346 . Alternatively, the stem  346  and the insert  342  may utilize any of a number of different structural features or components with which to couple and secure the insert  342  to the stem  346 . As a further alternative, any of a number of different processes may be employed to couple and secure the insert  342  to the stem  346  (e.g., using an interference fit, using adhesives, welding, etc.). 
         [0052]    With continued reference to  FIG. 21 , the base  350  of the insert  342  includes spaced grooves  382 ,  384  in which respective seals  386 ,  388  (e.g., O-rings) are positioned. Each of the seals  386 ,  388  is engaged with the interior wall  374  of the stem  346  about the inner periphery of the stem  346  to substantially prevent fuel from leaking between the insert  342  and the interior wall  374  of the stem  386 . Consequently, the stem  346  and the insert  342  at least partially define an air chamber  390 , located above the insert  342 , within the interior of the stem  346 . Specifically, the lower extent of the air chamber  390  is defined by an upper wall  394  of the base  350  which the idle circuit conduit  354  and the main circuit conduit  358  extend. The main circuit conduit  358  includes a plurality of apertures  398  fluidly communicating the main circuit passageway  366  and the air chamber  390 , the function of which is described in more detail below. 
         [0053]    With continued reference to  FIG. 21 , the insert  342  includes a lower wall  402  spaced from the upper wall  394 , and a jet  406  supported by the lower wall  402 . The walls  394 ,  402  define therebetween a fuel reservoir  410 , and the jet  406  includes an orifice  414  sized to meter fuel flow from the fuel bowl chamber  334  to the fuel reservoir  410 . In the illustrated construction of the carburetor  310 , the jet  406  is configured as a separate and distinct component from the insert  342  that is coupled to the insert  342  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). Alternatively, the jet  406  may be omitted, and the lower wall  402  may include an orifice substantially identical to the orifice  414  in the jet  406  to meter fuel flow from the fuel bowl chamber  334  to the fuel reservoir  410 . 
         [0054]    Respective ends  418 ,  422  of the idle circuit passageway  362  and the main circuit passageway  366  are in fluid communication with the fuel reservoir  410  to draw fuel directly from the fuel reservoir  410  during operation of the engine incorporating the carburetor  310 . Another jet  426  is coupled to the idle circuit conduit  354  at a location proximate an end  430  of the idle circuit passageway  362  opposite the end  418 . The jet  426  includes an orifice  434  sized to meter fuel flow that is discharged from or exiting the idle circuit passageway  362 . In the illustrated construction of the carburetor  310 , the jet  426  is configured as a separate and distinct component from the insert  342  and is coupled to the insert  342  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). Alternatively, the jet  426  may be omitted, and the end  430  of the idle circuit passageway  362  may be formed to include an orifice substantially identical to the orifice  434  in the jet  426  to meter fuel flow exiting the idle circuit passageway  362 . 
         [0055]    With continued reference to  FIG. 21 , the carburetor body  314  includes a receptacle  438  within the stem  346  into which the idle circuit conduit  354  is at least partially received. In the illustrated construction of the carburetor  310 , the receptacle  438  is at least partially defined by the interior wall  374  of the stem  346  and an arcuate wall  442  extending from the carburetor body  314  toward the fuel bowl  330 . Alternatively, the receptacle  438  may be defined by different structure of the carburetor body  314 . The idle circuit conduit  354  includes a groove  446  in which a seal  450  (e.g., an O-ring) is positioned. A portion of the seal  450  is engaged with the interior wall  374  of the stem  346 , and the remaining portion of the seal  450  is engaged with the arcuate wall  442  to substantially prevent any leakage of air from the air chamber  390  into the space above the seal  450 . 
         [0056]    With continued reference to  FIG. 21 , the carburetor body  314  includes an aperture  454  through which the main circuit conduit  358  extends. As a result, an end  458  of the main circuit passageway  366  opposite the end  422  is disposed in the air/fuel passageway  318  and is in fluid communication with the air/fuel passageway  18 . Specifically, the portion of the main circuit conduit  358  protruding into the air/fuel passageway  318  is disposed proximate a venturi  462  in the carburetor  310  ( FIG. 18 ). As a result, the end  458  of the main circuit passageway  366  is disposed in a region of relatively low pressure in the air/fuel passageway  318 , thereby allowing fuel to be drawn from the fuel reservoir  410 , via the main circuit passageway  366 , and into the air/fuel passageway  318  during part-throttle or full-throttle engine operation. Although the venturi  462  is integral with the carburetor body  314  as shown in  FIG. 18 , the venturi  462  may alternatively be configured as a separate insert like the venturi  162  shown in  FIG. 7 . 
         [0057]    With reference to  FIG. 19 , the carburetor body  314  includes a fuel passageway  466  defining a longitudinal axis  470 , and an idle circuit air bleed passageway  474 , defining a longitudinal axis  478  substantially parallel with the direction of the air/fuel passageway  318 , in fluid communication with the fuel passageway  466 . Specifically, the idle circuit air bleed passageway  474  includes an inlet  482  exposed to the upstream portion  324  of the air/fuel passageway  318 , and an outlet  486  exposed to a throttle progression pocket  490  formed in the carburetor body  314  (see also  FIG. 18 ). As shown in  FIGS. 18 and 19 , a jet  492  is coupled to the carburetor body  314  in the inlet  482  of the idle circuit air bleed passageway  474 . The jet  492  includes an orifice  493  sized to meter the airflow drawn into the idle circuit air bleed passageway  474 . In the illustrated construction of the carburetor  310 , the jet  492  is configured as a separate and distinct component from the carburetor body  314  that is coupled to the carburetor body  314  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). Alternatively, the jet  492  may be omitted, and the inlet  482  of the idle circuit air bleed passageway  474  may be formed to include an orifice substantially identical to the orifice  492  in the jet  492  to meter the airflow drawn into the idle circuit air bleed passageway  474 . 
         [0058]    With reference to  FIG. 19 , the fuel passageway  466  is in fluid communication with the idle circuit air bleed passageway  474  at a location between the inlet  482  and the outlet  486  of the idle circuit air bleed passageway  474 . The fuel passageway  466  is also in fluid communication with the idle circuit passageway  362  to receive fuel discharged from or exiting the idle circuit passageway  362  during operation of the engine. As such, as is described in more detail below, the fuel passageway  466  introduces fuel into the idle circuit air bleed passageway  474 , and the resultant air/fuel mixture is delivered to the throttle progression pocket  490  for use by the engine during idle. In the illustrated construction of the carburetor  310 , the respective axes  470 ,  478  of the fuel passageway  466  and the idle circuit air bleed passageway  474  are oriented substantially normal or orthogonal to each other and are contained within a common plane (e.g., plane  19 - 19  in  FIG. 17 ). Such an arrangement of the respective passageways  466 ,  474  facilitates molding the carburetor body  314  as a single piece, with the passageways  466 ,  474  being formed during the molding process. As such, subsequent machining processes are not required to create either of the respective passageways  466 ,  474 . 
         [0059]    With reference to  FIGS. 18 and 19 , a plurality of apertures  494  fluidly communicate the throttle progression pocket  490  with the downstream portion  328  of the air/fuel passageway  318 . As is described in more detail below, the throttle valve  326  progressively uncovers the apertures  494  as the throttle valve  326  opens from its substantially closed position at idle to provide a smooth transition from the idling to part-throttle or full-throttle operation of the engine. As shown in  FIG. 18 , the carburetor  310  includes a plug  498  coupled to the body  314  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). The plug  498  at least partially defines the pocket  490 , and substantially prevents air from being drawn into the pocket  490  to dilute the air/fuel mixture in the pocket  490 . 
         [0060]    With reference to  FIG. 20 , the carburetor body  310  includes a main circuit air bleed passageway  502  having an inlet  506  exposed to the upstream portion  324  of the air/fuel passageway  318 , and an outlet  510  exposed to the air chamber  390  in the interior of the stem  346  (see also  FIG. 21 ). As shown in  FIG. 18 , a jet  512  is coupled to the carburetor body  314  in the inlet  506  of the main circuit air bleed passageway  502 . The jet  512  includes an orifice  513  sized to meter the airflow drawn into the main circuit air bleed passageway  502 . In the illustrated construction of the carburetor  310 , the jet  512  is configured as a separate and distinct component form the carburetor body  314  that is coupled to the carburetor body  314  (e.g., using a press-fit or an interference fit, using adhesives, by welding, etc.). Alternatively, the jet  512  may be omitted, and the inlet  506  of the main circuit air bleed passageway may be formed to include an orifice substantially identical to the orifice  513  in the jet  512  to meter the airflow drawn into the main circuit air bleed passageway  502 . 
         [0061]    In the illustrated construction of the carburetor  310 , the main circuit air bleed passageway  502  includes a first portion  514  having the inlet  506  at one end and defining a longitudinal axis  518  that is oriented horizontally relative to the point of view of  FIG. 10 . The main circuit air bleed passageway  502  also includes a second portion  522  having the outlet  486  at one end and defining a longitudinal axis  526  that is oriented vertically relative to the point of view of  FIG. 20 . In the illustrated construction of the carburetor  310 , the longitudinal axes  518 ,  526  of the respective first and second portions  514 ,  522  of the main circuit air bleed passageway  502  are oriented normal or orthogonal to each other to facilitate molding the carburetor body  314  as a single piece, with the passageway  502  being formed during the molding process. As such, subsequent machining processes are not required to create either of the portions  514 ,  522  of the passageway  502 . 
         [0062]    With reference to  FIG. 22 , the carburetor body  314  also includes a priming passageway  530  in fluid communication with the fuel bowl chamber  334 . The priming passageway  530  includes an inlet  532  (see  FIGS. 12 and 18 ) positioned in a flange of the body  314  configured for mounting to an air cleaner assembly (not shown) of the engine incorporating the carburetor  310 . The air cleaner assembly may include a primer bulb and another priming passageway, in which the primer bulb is at least partially disposed, in fluid communication with the inlet  532  of the priming passageway  530 . With reference to  FIG. 11 , carburetor  310  includes a plug  534  positioned in the priming passageway  530 . Although not shown, the plug  534  may include a small aperture or orifice to provide external venting of the fuel bowl chamber  334 . The small aperture or orifice in the plug  534  may also be sized to tune the amount of primer charge that results when an operator of the engine depresses the primer bulb in the air cleaner assembly to prime the carburetor  310  prior to starting the engine. Specifically, an operator may depress the primer bulb to displace the air in the priming passageway  530  down into the fuel bowl chamber  534 , thereby displacing a substantially equivalent volume of fuel through the insert  342  (e.g., via the main circuit passageway  362 ) and into the air/fuel passageway  318  to enrichen the air/fuel mixture delivered to the engine during startup. 
         [0063]    In operation of the carburetor  310  during engine idling, the region of relatively low pressure downstream of the throttle valve  326 , when oriented in a substantially closed position, creates an airflow through the idle circuit air bleed passageway  474  which, in turn, draws fuel from the fuel bowl chamber  334 , through the orifice  414  in the jet  406 , and into the fuel reservoir ( FIG. 19 ). Fuel is subsequently drawn from the fuel reservoir  410 , through the idle circuit passageway  362 , through the orifice  434  in the jet  426 , through the fuel passageway  466  in the carburetor body  314 , and into the idle circuit air bleed passageway  474 , where the fuel mixes with the air in the passageway  474 . The air/fuel mixture in the idle circuit air bleed passageway  474  then moves into the throttle progression pocket  490 , where the air/fuel mixture may be drawn through one of the apertures  494  and into the air/fuel passageway  318  to maintain the engine idling. As the throttle valve  326  opens from its substantially closed position, more of the apertures  494  are uncovered to draw a progressively increasing amount of air/fuel mixture from the pocket  490 , thereby providing a smooth transition to part-throttle or full-throttle engine operation. 
         [0064]    During part-throttle or full-throttle engine operation, the region of relatively low pressure surrounding the portion of the main circuit conduit  358  protruding into the air/fuel passageway  318  creates an airflow through the main circuit air bleed passageway  502  and draws fuel from the fuel bowl chamber  334 , through the orifice  414  in the jet  406 , and into the fuel reservoir  410  ( FIG. 21 ). Fuel is subsequently drawn from the fuel reservoir  410  and through the main circuit passageway  366 , which causes air in the air chamber  390  to be drawn through the apertures  398  and into the main circuit passageway  366  to mix with the fuel in the main circuit passageway  366 . The resultant air/fuel mixture in the main circuit passageway  366  is discharged directly into the air/fuel passageway  318  for use by the engine during part-throttle or full-throttle operation. The projection  360  occupies space in the air chamber  390  and therefore reduces the effective volume of the air chamber  390 . In addition, because the projection  360  is in facing relationship with the outlet  510  of the main circuit air bleed passageway  502 , the projection  360  facilitates distribution of the airflow entering the air chamber  390  throughout the air chamber  390 . 
         [0065]    Various features of the invention are set forth in the following claims.