Abstract:
A compact engine start device of a combustion engine rotary-type carburetor overrides normal operation of a rotary throttle valve to provide a richer mixture of fuel-and-air to start a cold engine. Rotation of a start lever of the start device activates a releasable camming interface coupler causing the throttle lever to rotate about a rotary axis and axially lift partially out of the carburetor at prescribed angular and axial distances. This provides the engine, through a fuel-and-air mixing passage, with a controlled and enriched ratio and volume of a fuel-and-air mixture. Preferably, the start lever has a projecting rod that inserts into a hole in the carburetor body for rotation about an axis orientated substantially parallel to the rotary axis. An outward surface of the start lever is in rotational sliding contact with a low-profile, preferably cantilevered, retention arm preferably formed unitarily to a metering fuel pump cover engaged removably to the body of the carburetor, thus allowing rotational movement but preventing axial movement of the start lever. Because the start lever does not move axially to displace the rotary throttle valve, the height of the start lever is favorably minimized. Moreover, the start lever preferably has a knob for user interface at a distal end of the lever that conforms generally about the retention arm thus maximizing knob size yet not contributing to an increase in carburetor size.

Description:
RELATED APPLICATIONS 
     Applicants claim priority of Japanese Application No. 2005-026219, filed Feb. 2, 2005. 
     FIELD OF THE INVENTION 
     The present invention relates to a rotary valve carburetor for a combustion engine and more particularly to an engine start device of the carburetor. 
     BACKGROUND OF THE INVENTION 
     Known rotary-type carburetors have a fuel-and-air mixing passage orientated through a body for flowing a controlled ratio and volume of a fuel-and-air mixture to a combustion engine. This control is generally provided by a throttle valve rotatably and axially movable in a cylindrical cavity transverse to the mixing passage. A cylindrical portion of the throttle valve located in the cavity carries a through-bore that when rotated generally aligns adjustably to the mixing passage generally controlling the mixture flow rate. The cylindrical portion also supports a needle orientated concentrically to a rotary axis of the throttle valve and projecting into the through-bore for receipt into an open end of an axially confronting fuel feed tube supported by the carburetor body. A cylindrical wall of the feed tube carries an orifice opening into the through-bore for the flow of liquid fuel into the mixing passage and from a fuel metering chamber communicating with the feed tube. Axial movement of the rotary throttle valve shifts the needle axially with respect to the feed tube thus adjustably obstructing the orifice thereby controlling fuel flow into the through-bore and mixing passage. 
     Generally, a cammed interface between the cylindrical portion of the throttle valve and the carburetor body acts to move the throttle valve axially in response to rotational movement of the same. Rotational movement is achieved through operator intervention generally placed upon a throttle lever disposed outside of the carburetor body and typically engaged to the cylindrical portion via a rotatable valve shaft. 
     Such rotary-type carburetors are known to have engine start devices that act to supply an enriched fuel-and-air mixture to a cold engine for starting. These start devices typically carry cam surfaces required to cause axial movement of the throttle valve. Unfortunately, known start devices have numerous parts and the known cam surfaces require structure that projects further outward from the carburetor body than does the throttle lever at its furthest axial withdrawn (wide open) state thus considerably enlarging the carburetor size. Moreover, known start levers having a handle or knob at a distal end for leverage that must also project a considerable distance from the carburetor body hindering a desirable compact carburetor design. 
     SUMMARY OF THE INVENTION 
     A compact engine start device of a combustion engine carburetor interfaces with a rotary throttle valve of the carburetor that operatively intersects a mixing passage extending through a body of the carburetor. Preferably, a camming mechanism is carried between the rotary throttle valve and the body for axially moving the valve along a rotary axis to generally adjust the quantity of fuel flow into the mixing passage as the valve rotates about the rotary axis for generally adjusting the quantity of air flow through the mixing passage, thereby establishing a generally consistent fuel to air ratio. The start device preferably operates to disengage the camming mechanism and provide a richer mixture of fuel and air for starting the engine. 
     Rotation of a start lever of the start device causes the start lever to circumferentially contact an abutment of a throttle lever of the throttle valve while axially engaging a releasable camming interface coupler carried between the throttle lever and the start lever for moving the throttle lever axially as it is rotated about a rotary axis by the start lever. The camming interface coupler causes the throttle lever to axially lift partially out of the carburetor at prescribed angular and axial distances while disengaging the camming mechanism utilized by the rotary throttle valve during normal operation of the engine. The prescribed angular and axial positions of the throttle lever as generally established by the camming interface coupler when the start lever is in contact with the throttle lever increases the enrichment of a fuel and air mixture flowing through the mixing passage for engine cold starting relative to when the camming mechanism is engaged during normal operation. 
     Preferably, the start lever has a projecting rod that inserts into a hole in the carburetor body for rotation about an axis orientated substantially parallel to and spaced radially outward from the rotary axis. An outward surface of the start lever is in rotational sliding contact with a low-profile, preferably cantilevered, retention arm preferably formed unitarily to a metering fuel pump cover of the body of the carburetor, thus allowing rotational movement while preventing axial movement of the start lever. Because the start lever does not move axially to axially displace the rotary throttle valve, the height of the start lever is favorably minimized. Moreover, the start lever preferably has a leveraging knob for user interface at a distal end of the lever that conforms generally about the retention arm for maximizing its size while not contributing to an increase in overall carburetor size. 
     The releasable camming interface coupler preferably has a step-sloped camming surface carried by the start lever that is slidably in contact with an arcuate rib carried by the throttle lever. Preferably, the arcuate rib projects toward a carburetor body and lies generally within an imaginary plane orientated perpendicular to the rotary axis. Rotation of the start lever from a rest position causes the camming surface to generally move between the body and the throttle lever thereby engaging the arcuate rib and urging it in a substantially axial direction while the start lever circumferentially contacts an abutment on the throttle lever. With continued rotation of the start lever, this contact causes the throttle lever to rotate in a counter rotational direction and the sloped camming surface to axially lift the throttle lever. When the releasable camming interface coupler is so engaged the conventional cam mechanism of the rotary carburetor disengages between the body and the rotary throttle valve. 
     Objects, features and advantages of this invention include a compact design of a rotary valve carburetor having an engine start device that automatically disengages during normal engine operation, improves cold engine starts, enhances operator confidence via the felt indenting of the camming interface coupler, improved leveraging for engaging the engine start device, fewer parts, relatively simple design, inexpensive to manufacture and assemble, robust, easily adjustable and maintained, reliable, durable and in service has a long useful life. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of this invention will be apparent from the following detailed description, appended claims and accompanying drawings in which: 
         FIG. 1  is a perspective view of a rotary-type carburetor having an engine start device embodying the present invention; 
         FIG. 2  is a fragmentary cross section of the rotary-type carburetor taken along broken line  2 - 2  of  FIG. 1 ; 
         FIG. 3  is an exploded partial perspective view of the rotary-type carburetor; 
         FIGS. 4A to 4C  are perspective views showing a process of assembling a return spring to a start lever of the engine start device; 
         FIG. 5  is an exploded perspective view showing how a pump cover is assembled; 
         FIG. 6A  is plan view showing the start lever in a rest position; 
         FIG. 6B  is an enlarged fragmentary section view showing a cam interface coupler of the engine start device in the rest or disengaged position and taken along line  6 B- 6 B of  FIG. 6A ; 
         FIG. 7A  is a view similar to  FIG. 6A  in a first starting mode; 
         FIG. 7B  is a view similar to  FIG. 6B  in the first starting mode; 
         FIG. 8A  is a view similar to  FIG. 6A  in a second starting mode; and 
         FIG. 8B  is a view similar to  FIG. 6B  in the second starting mode. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As best illustrated in  FIGS. 1 and 2 , a rotary valve carburetor  30  embodying a start engine device  32  of the present invention has a fuel-and-air mixing passage  2  extending through a main body  1 . A substantially cylindrical cavity  1   a  carried by the body  1  extends transversely across the mixing passage  2  for generally rotatable and axially movable receipt of a rotary throttle valve  3 . The rotary throttle valve  3  has a cylindrical portion  3   c  that rotates about and moves axially with respect to a rotary axis  34  disposed substantially perpendicular to the mixing passage  2 , and a through-bore  3   a  orientated generally perpendicular to the rotary axis  34  and extending transversely through the cylindrical portion  3   c . The through-bore  3   a  is orientated so that the degree or extent of communication with the fuel-and-air mixing passage  2  varies between a fully closed state and a fully open state. Preferably, the lower part of the carburetor main body  1  has a first segment or mid plate  11  defining in part a fuel metering chamber (not shown) and an interfacing lower segment or plate  12  defining in part a reference chamber usually at near atmospheric pressure. A resilient diaphragm  36  sealed preferably along a peripheral edge between the plates  11 ,  12  defines in-part the fuel chamber on one side and the reference chamber on an opposite dry side. 
     The fuel metering chamber receives liquid fuel from a fuel pump  13  preferably orientated on one side of the carburetor  30 . The fuel pump  13  has a fuel chamber defined by a face carried by the carburetor main body  1 , a pulsating pressure chamber defined in-part by a pump cover  14  of the body  1  generally attached to the face of the carburetor main body  1 , and a reed or check valve (not shown) preferably formed by a flexible membrane or the like interposed between the face of the carburetor main body  1  and the pump cover  14  of the body  1 . The pulsating pressure chamber on the side of the pump cover  14  preferably communicates with the crankcase chamber of the internal combustion engine so that the pulsating pressure of the crankcase chamber provides a pumping action for producing a prescribed fuel supply to the fuel metering chamber in the fuel metering chamber plate  11 . 
     A stationary fuel nozzle or fuel feed tube  6  supplies fuel to the mixing passage  2  from the fuel metering chamber which is at a substantially constant pressure as provided by operation of the metering diaphragm  36 . The fuel nozzle  6  projects into the through-bore  3   a  and slidably receives the axially opposed fuel metering needle  7  of the throttle valve  3  which is carried by the cylindrical portion  3   c  and extends along the rotary axis  34  to project into the through-bore  3   a . The tip of the fuel metering needle  7  is received in the fuel nozzle  6  for control of liquid fuel flow. The cylindrical wall of the fuel nozzle  6  is provided with an orifice or fuel jet  6   a  at a point corresponding to the tip of the fuel metering needle  7  along the axial direction. 
     The rotary throttle valve  3  preferably has a valve shaft  3   b  projecting co-axially upward from the cylindrical portion  3   c , extending out of the carburetor main body  1 , and attached to a radially projecting throttle lever  4 . The cross sectional flow area of the fuel-and-air mixing passage  2  is controlled by the angular position of the rotary throttle valve  3 . Simultaneously, the cross sectional flow area of the orifice  6   a  is varied by axial displacement of the fuel metering needle  7  to control the amount of liquid fuel flowing into the through-bore  3   a . The cross sectional flow area of the orifice  6   a  corresponds to the change in the cross sectional flow area of the fuel-and-air mixing passage  2  during normal operation of the engine. 
     The lower opening of the valve cavity  1   a  is preferably closed by a plug member  11   a  of the fuel metering chamber plate  11  of the body  1 . A disengagable cam mechanism  8 , orientated axially between the plug member  11   a  and the lower surface of the rotary throttle valve  3 , axially moves the rotary throttle valve  3  in dependence on the angular position thereof. The disengagable cam mechanism  8  preferably has a cam surface (not shown) having a slope formed on the lower surface of the rotary throttle valve  3  and a cam follower member provided on the plug member  11   a  of the body  1  that slides over the cam surface. At the upper opening of the valve cavity  1   a  is an annular shoulder  38  of the body  1  projecting radially inward and disposed axially over the cylindrical portion  3   c  of the rotary throttle valve  3 . Generally interposed axially between the annular shoulder  38  and the cylindrical portion  3   c  of the rotary throttle valve  3  is a coiled compression spring  9  that not only resiliently, and axially urges the cam surface of the rotary throttle valve  3  against the cam follower member on the top side of the plug member  11   a  but also serves as a torsion spring to resiliently urge the cylindrical portion  3   c  of the rotary throttle valve  3  toward its fully closed position. 
     Preferably, an operator remotely rotates the throttle lever  4  using a Bowden or control cable  16  that connects to a coupler  15  projecting upward from and engaged rotationally to the throttle lever  4  at a radial distance from the rotary axis  34  for leverage. The coupler  15  is preferably substantially cylindrical in shape and has a diametrically extending slit  40  opening upward for receipt of an enlarged end of the cable  16 . 
     The engine start device  32  of the carburetor  30  generally includes a rotatable start lever  21  mounted rotatably on the carburetor body  1  about an axis  42  spaced radially outward from and disposed substantially parallel to the rotary axis  34  of the throttle lever  4 . A short rod  21   a  of the start lever  21  is disposed concentrically to the axis  42  and preferably projects unitarily downward from an inward surface  44  of the start lever  21  (as best shown in  FIGS. 2 and 3 ). Preferably, the rod  21   a  is snugly and rotatably received in a hole or bore  1   b  carried by the body  1 . Rotation of the start lever  21  about the axis engages a cam interface coupler  33  carried between the start lever  21  and the throttle lever  4  for generally disengaging the camming mechanism  8  and moving the throttle valve axially to enrich the fuel and air mixture generally for cold engine starts. 
     The start lever  21  carries a cam  22  of the cam interface coupler  33  that can be selectively orientated and engaged with the throttle lever  4  to position the throttle valve for cold starting of the engine. Rotating the start lever  21  about the axis  42  engages the cam  22  with the throttle lever  4 , thus generally disengaging the camming mechanism  8  by axially lifting the cylinder portion  3   c  of the throttle valve  3  away from the plug member  11   a  and against the biasing force of the yieldable compression spring  9 . The start lever  21  thus interacts with the throttle lever  4  for rotating the rotary throttle valve  3  to a prescribed angular position and, at the same time, axially moving the throttle valve by a prescribed axial distance which disengages the camming mechanism  8  when cold starting the engine. This prescribed throttle valve position increases the supply of liquid fuel thus increasing the enrichment of the fuel-and-air mixture required for cold starting the engine. 
     As best illustrated in  FIGS. 2 &amp; 5 , the start lever  21  is retained axially in the bore  1   b  by a generally wide and substantially planar retention arm  14   a  cantilevered over the start lever and projecting at a substantially right angle and unitarily from a base support member  14   b  that preferably projects outward from the pump cover  14 . The cantilevered retention arm  14   a  projects outward from the base support member  14   b  so as to overhang the start lever  21  and generally form a clearance  46  between a distal or suspended end  14   d  of the arm  14   a  for a portion of the start lever  21  to rotate out of when moving from the rest position and toward the engaged position. A substantially friction-free sliding surface  14   c  carried by the retention arm  14   a  is in sliding engagement with an axially opposing outward surface  48  of start lever  21 . 
     The start lever  21  is elongated and extends radially with respect to axis  42 . A first end of the start lever  21  projects generally toward the throttle lever  4  and carries the cam  22  and a substantially diametrically opposite second end of the start lever  21  projects radially outward to form a corrugated thumb hold or knob  21   c  for the operator to grasp with a finger or thumb without slippage. The throttle lever  4  has a fan-shaped portion  4   a  extending axially outward and carrying a circumferentially extending, arcuate, and downward projecting cam engagement portion or rib  4   b  of the camming interface coupler  33  that generally confronts the cam  22  for moving the throttle lever  4  axially outward. Preferably, the start lever  21  and the cam  22  are preferably unitary and manufactured as a single part. The throttle lever  4  including the rib  4   b  is preferably stamped during manufacturing from a single metallic plate. 
     As best illustrated in  FIGS. 1 ,  3  and  5 , the start lever  21  is provided with a threaded adjuster or screw  24  for adjustment of the angular position of the lever  21  relative to the throttle lever  4  at the time of contact. The metallic throttle lever  4  is formed or stamped with a bent planar tab  4   c  projecting from a peripheral part of the throttle lever  4  and toward the carburetor body  1  and substantially lying in an imaginary plane disposed parallel to the rotary axis  34  of the valve shaft  3   b . An abutment or abutment tab  4   d  projects radially inward from a rotationally trailing edge of the bent tab  4   c  and lies within an imaginary plane orientated substantially perpendicular to the bent tab  4   c . As the start lever  21  is turned from the initial or rest position, the free end of the adjustment screw  24  eventually contacts the abutment tab  4   d  provided the throttle lever  4  is in the closed position, and further rotation of the start lever  21  causes the throttle lever  4  to rotate in a counter direction toward the open position. The width (i.e. radial projection) of the abutment tab  4   d  is determined in such a manner that the adjustment screw  24 , although sliding thereon, continues to bear on the abutment tab  4   d  while the throttle lever  4  is turned to an angular position or mode suitable for starting the engine. 
     In operation, the arcuate rib  4   b  of the fan-shaped portion  4   a  of the throttle lever  4  initially engages the cam  22  when the throttle lever  4  is in the fully closed position and the start lever  21  is initially being turned toward an engine start position or mode. To automatically avoid this camming engagement when the engine is operating in a normal condition other than a starting condition, the start lever  21  is fitted with a return, torsional, coil spring  23  engaged at opposite ends between the start lever  21  and the body  1  so that the start lever  21  is urged or biased to the rest position under the spring force of the return spring  23 . As best shown in  FIGS. 6A and 6B , when the start lever  21  is in the rest position the cam  22  of the start lever  21  and fan-shaped portion  4   b  of the throttle lever  4  are mutually out of engagement or de-coupled. Therefore, the rotary throttle valve  3  is in the fully closed position and the disengagable cam mechanism  8  of the rotary throttle valve  3  is functional and engaged. 
     Referring to  FIGS. 6A-6B , the cam  22  of the start lever  21  is provided with a stepped shape including two levels so that the throttle valve rotational opening angle and fuel supply at the time of cold starting the engine may be varied depending on the particular situation. It may also have three or more levels. The cam  22  is formed with a leading first slope or cam surface  22   a , a first indent or groove  22   b , then a second slope or cam surface  22   c  and a trailing second recess or groove  22   d . The bottom surface of the first groove  22   b  is higher than the lower rib  4   b  of the fan-shaped portion  4   a  when the throttle valve  3  is in the fully closed position (with the camming mechanism  8  engaged) by a prescribed distance, and the bottom surface of the trailing second groove  22   d  is higher than the bottom surface of the first engagement portion  22   b  by a prescribed distance. The first and second grooves  22   b  and  22   d  lie within respective imaginary planes disposed substantially perpendicular to the rotary axis  34 . 
     When the downward rib  4   b  rides over the first slope or cam surface  22   a  and falls into the first groove  22   b , there is a detent action felt by the operator. Similarly, when the downward rib  4   b  rides over the second slope or cam surface  22   c  and falls into the second groove  22   d , there is also a detent action felt by the operator. Thereby, the operator can easily place the start lever  21  in the positions for the first starting mode and second starting mode without any difficulty. The engagement surfaces of the two grooves  22   b  and  22   d  are generally arcuate and oriented in such a manner that they enable a prolonged contact interface with the downward projecting and elongated rib  4   b  depending on the angular position of the start lever  21  so that a state of secure and continued engagement can be achieved. 
     When cold starting the engine, an operator first grasps the corrugated knob  21   c  of the start lever  21  and thereby partially rotates the start lever  21  as indicated by arrow A in  FIG. 6A . This rotational movement causes the cam  22 , carried by the generally opposite front end of the start lever  21 , to slide in the direction indicated by arrow B in  FIG. 6B . When the start lever  21  is turned further from the position illustrated in  FIG. 6A , the rib  4   b  of the throttle lever  4  slides over the leading first slope or cam surface  22   a , thus axially lifting of the throttle valve  3  while the adjustment screw  24  of the start lever  21  engages the abutment tab  4   d  of the throttle lever  4 . With continued rotation of the start lever  21 , the adjustment screw  24  pushes the abutment tab  4   d  as the distal end face of the adjustment screw  24  generally slides (in a radially outward direction) over the surface of the abutment tab  4   d  with the result that the throttle lever  4  turns in the opening direction indicated by arrow C in  FIG. 6A  in synchronism with the rotation of the start lever  21 . 
     When the start lever  21  is turned by a certain angle and has reached the position indicated in  FIGS. 7A and 7B , the first slope or cam surface  22   a  has moved past the arcuate rib  4   b  and engages the first engagement portion  22   b . This is the first starting mode reflecting a relatively small valve opening angle and a small fuel supply that is a desirable start position when the engine temperature is not significantly cold. Because the camming mechanism  8  of the rotary throttle valve  3  is preferably disengaged automatically by rotation of the start lever  21  (i.e. the cylinder portion  3   c  is lifted axially more than the axial lift created by mere rotation upon the camming mechanism), the fuel-and-air mixture produced with this orientation is richer than normal operation of the throttle valve when the camming mechanism is engaged. 
     When the start lever  21  is turned further and has reached the position indicated in  FIGS. 8A and 8   b , it rides over the second slope or cam surface  22   c  and moves past the arcuate rib  4   b , and the rib  4   b  engages or generally snaps into the trailing second groove  22   d . This creates a second starting mode reflecting a valve opening angle and a fuel supply that are greater than those of the first starting mode. When the engine temperature is significantly cold and an increased difficulty is expected in starting the engine, the richer mixture of the second starting mode is desirable. 
     Once the engine starts, the starting mode of the engine start device  32  may be terminated by utilizing the control cable  16  to further open the throttle valve  3 . During this rotation of the throttle valve  3 , the cylindrical portion  3   c  of the rotary throttle valve  3  does not substantially axially move, however, the camming mechanism  8  does move toward re-engagement. With continued rotation of the throttle valve  3 , the circumferentially extending rib  4   b , and the engagement between rib  4   b  and the groove  21   b  or  21   d  of the start lever  21  is released with the result that the start lever  21  returns to the rest position under the action of the return spring  23 , and the camming mechanism  8  re-engages either smoothly or by a slight axial fall of the throttle lever  4  and cylinder portion  3   c.    
     The initial rotation of the throttle lever  4  without axial movement of the throttle valve  3  increases the cross section flow area of the through-bore  3   a . This increases air flow without generally increasing liquid fuel flow thus leaning-out the rich mixture of fuel and air after the engine starts. Moreover, any slight axial fall of the throttle valve  3  when the throttle lever releases from the start lever also has the affect of leaning out the rich mixture of fuel and air otherwise needed for cold starting of the engine. Thus, without taking any special action, the cold starting mode can be readily terminated simply by opening the throttle valve  3  in a normal way, and it is possible to move on from the starting mode to the leaner normal operation mode in a smooth fashion. 
     When the control cable  16  is not attached to the coupler  15 , it is possible to turn the throttle lever  4  in the valve opening direction by directly operating an engagement releasing handle  4   e  of the throttle lever  4 . This allows the throttle valve  4  to be opened when testing the carburetor  30  on the manufacturing assembly line. Also, the control cable  16  can be easily connected to the coupler  15  during the assembly process by turning the throttle lever  4  in such a direction as to bring the coupler  15  closer to the control cable  16 . Because the downward rib  4   b  extends circumferentially at a constant radius, the engagement with grooves  22   b  or  22   d  can be maintained even while the throttle lever  4  is turned in the start mode and with the camming mechanism  8  disengaged. In other words, the valve opening angle can be freely changed within a limited range while keeping the supply of fuel at a fixed level, and this range can be shifted by turning the adjustment screw  24  allowing fine adjustment of the starting mode. 
     During the manufacturing process, the cylindrical valve cavity  1   a  is preferably open at the lower end to permit axial insertion of the cylindrical portion  3   c  and shaft  3   b  of the rotary throttle valve  3 . The annular shoulder  38  of the body  1  is located at the opposite upper end of the cavity  1   a  and defines a concentrically located circular hole through which the valve shaft  3   b  passes. 
     As best illustrated in FIGS.  2  and  4 A- 4 C and during manufacture of the carburetor  30 , the coiled return spring  23  is slipped axially over the short rod  21   a  of the start lever  21 . A first coil end  23   a  of the return spring  23  is fit into an engagement groove formed in the lower surface of the start lever  21  (facing the carburetor body  1  when fully assembled) as shown in  FIG. 4B . The fit of the first end circumferentially aligns an opposite coil end  23   b  of the return spring  23  with respect to the axis  42  and axially places the end  23   b  adjacent to the lower surface of the start lever  21  as shown in  FIG. 4C , thus staging the start lever  21  and spring  23  for mounting on the carburetor body  1 . 
     The coil end  23   b  is shaped like a hook and is pre-staged or positioned to form in-part a circular opening also defined in-part by the start lever  21 , as best shown in  FIG. 4C . The carburetor main body  1  is formed with a projecting engagement stud  1   c  dimensioned to be received in this circular opening (see  FIGS. 2 and 3 ). The start lever  21  having the return spring  23  provisionally mounted thereon is mounted on the carburetor main body  1  with the short rod  21   a  fitted into the hole  1   b  and the engagement stud  1   c  fitted into the circular opening defined jointly by the other end  23   b  and the corresponding part of the start lever  21  when assembled. 
     As best illustrated in  FIG. 3 , during assembly the throttle lever  4  is rotated toward the fully open position thus placing the fan-shaped portion  4   a  of the throttle lever  4  circumferentially clear of the adjustment screw  24  when mounting the start lever  21  on the carburetor main body  1  from above. When assembling the staged start lever  21 , the short rod  21   a  is fitted into the hole  1   b  before the pump cover  14  is mounted, thus preventing interference by the cantilevered retention arm  14   a . When the pump cover  14  is mounted on the side of the carburetor main body  1  from a perpendicular direction with respect to the rotary axis  34 , the start lever  21  is rotated to a maximum angular position away from the rest position or to the second start mode so that the cantilevered retention arm  14   a , formed unitarily as one piece with the pump cover  14 , does not interfere with the knob  21   c  of the start lever  21 . Preferably, the pump cover  14  of body  1  secured and sealed to the remaining portion of carburetor body  1  by a plurality of fasteners or threaded bolts  25 . 
     By adopting this assembling process, it is possible to maximize or increase the size of knob  21   c  for improved interaction with a finger or thumb of an operator and reduce the height of the start lever  21  (the projection from the upper surface of the carburetor main body  1 ) so that the projection of the components (including the retention arm  14   a ) of the carburetor  30  where the start lever  21  is provided can be minimized. 
     As best illustrated in  FIG. 1 , preferably the cantilevered retention arm  14   a  of the pump cover  14  has an idle adjustment screw  26  that is threadably movable along the length of the cantilevered retention arm  14   a . By abutting the front end of the idle adjustment screw  26  on the bent piece  4   c  of the throttle lever  4  in the fully closed position and turning the idle adjustment screw  26 , the rotary throttle. valve  3  can be positioned at any desired angular position against the spring force of the coiled compression spring  9  thus adjusting the idle speed of an engine. 
     The projection of the start lever  21  from the carburetor body  1  is minimal. It generally does not project outward further than the throttle lever  4  and thus does not increase the size or bulkiness of the rotary carburetor that would otherwise hinder packaging of the carburetor to an engine driven apparatus. This is achieved because the short rod  21   a  of the start lever  21  projects toward the carburetor main body  1  from a contoured inward surface of the start lever  21  while an opposite outward surface  48  of the start lever  21  that faces outward from the carburetor body  1  is relatively smooth and planar for substantially frictionless rotational sliding against the cantilevered retention arm  14   a  of the pump cover  14 . Moreover, the required thickness of the retention arm  14   a  for structural support is minimal due in-part to it&#39;s large width or spanning girth. 
     As a modification to the present invention, a short rod could be provided on the outward surface  48  of the start lever  21  facing the retention arm  14   a . However, the retention arm  14   a  would have to be made of a separate member attached to the pump cover  14  and the number of component parts would thus increase because the retention arm  14   a  would otherwise interfere with the short rod when assembling the start lever  21 . 
     As another modification to the present invention, the start lever  21  could be provided with a short rod that projects from both sides of the start lever  21 . However, the hole  1   b  of the carburetor main body  1  and the bearing for the other end of the short rod have to be aligned with a high precision for the start lever  21  to be able to turn in a smooth fashion. On the other hand, by supporting the upper surface  48  of the start lever  21  with the retention arm  14   a  via a surface contact and making the retention arm  14   a  large enough to support the start lever  21  over the entire range of the angular movement thereof, it is possible to allow the start lever  21  to be turned over the entire angular range in a smooth fashion without requiring any centering with high precision. 
     While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms, modifications or ramifications of the invention. It is understood that terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention as defined by the following claims.