WO1996012883A1 - Temperature conpensated fuel jet - Google Patents

Abstract

A fuel supply system (1) for an internal combustion engine, arranged in a suction channel (2) leading to the very engine body, said system comprising one or several nozzles (3, 3'), at least one nozzle (3) being configured in such a manner that its fuel through-flow resistance changes upon temperature changes because a movable part (5) in the nozzle being connected to a temperature-responsive member (6), such as a bimetal member (6), whereby the movable part (5), upon lower temperature levels, is moved by the member (6) for reduction of the fuel through-flow resistance, usually by an increase of the fuel through-flow opening, and thus the fuel through-flow is increased and a richer fuel mixture is obtained, i.e. a temperature compensation of the fuel supply with the aid of a temperature-compensated nozzle (3).

Description

Temperature compensated fuel jet

Technical Field

The subject invention relates to a fuel-supply system for an internal combustion engine, arranged in a suction channel leading to the engine body proper, said system comprising one or several nozzles.

Background of the Invention

In an internal combustion engine the relation between the amounts of fuel and of air sucked into the engine, the so called air- fuel-ratio, is of vital importance. For cold starts the engine is choked to provide a richer fuel mixture, i.e. a mixture with a higher fuel content. This is a necessity since fuel condensates on the walls of the suction channel and the combustion chamber to very high extent under these conditions. Also after start ups of the engine and cease of choking, i.e. during normal operation, the air-fuel ratio is affected by several factors, such as the air pressure and the air temperature. In membrane carburettors, for instance, the air- fuel mixture becomes leaner at lower temperatures. This is not desirable, since an equally rich or even a somewhat richer mixture is required at these temperature levels compared with normal temperatures. Modern carburettors normally are adjustable, giving the operator an opportunity to adjust the carburettor to various operational conditions, for instance to set the carburettor for a richer fuel mixture during the winter season. However, adjustable carburettors will not be permissible in the future on account of emission-preventive legi¬ slation. In many cases, the carburettors will be required to comprise built-in temperature compensation features, preventing too lean air- fuel mixtures at low temperatures. The same is true also with respect to injection systems positioned in a suction channel leading to the engine body proper. The Purpose of the Invention

The purpose of the subject invention is to considerably reduce the above outlined problem by creating automatic temperature com¬ pensation of the fuel supply.

Summary of the Invention

The above purpose is achieved by providing the fuel supply system in accordance with the invention with the characteristic features defined in the appended claims. The fuel supply system in accordance with the invention thus essentially is characterized in that at least one nozzle is conceived in such a manner that its fuel through- flow system changes upon temperature changes as a result of a movable part in the nozzle being secured to a temperature-responsive member, for instance a bimetal member, such that as a result the movable part is moved by the member at lower temperatures, resulting in reduced fuel through flow resistance, usually as a result of an increase of the fuel through-flow opening, and thus the fuel through-flow increases and a richer fuel mixture is obtained, i.e. temperature compensation of the fuel supply with the aid of a temperature compensated nozzle. The basic function thus is to decrease the fuel through-flow resistance at lower tempera¬ ture levels in response to the movement of the movable part with the aid of a temperature-responsive member, for instance a bimetal mem¬ ber. Usually, the movable part, such as a metering needle, is moved axially to increase the fuel through-flow opening. However, the mov¬ able part could also have a different shape and also be moved later¬ ally. In principle, it is likewise possible to change the fuel through- flow resistance without significantly change the fuel through-flow opening. In this case, the opening would have a very disadvantageous shape, for instance an elongate and narrow shape which would increase the resistance. The temperature-compensated nozzle may be used as the principal nozzle and/ or as the starter nozzle in a carbu¬ rettor. It could likewise be used as a nozzle in an injection system positioned in a suction channel. Both the principal nozzle and the starter nozzle could have several outlet openings in the suction channel. In the following, the designations principal nozzle and starter nozzle will be used irrespective of the number of injection openings in the suction channel. The temperature-compensated nozzle could work alone or could be connected in parallel or in series with another nozzle which is fixed or adjustable. These and other characteristic features and advantages will become more apparent from the follow- ing detailed description of various embodiments with the support of the annexed drawings.

Brief Description of the Drawings

The invention will be described in closer detail by means of various embodiments with reference to the accompanying drawings, wherein

Fig. 1 is a cross-sectional lateral view of a conventional mem¬ brane carburettor in which the fuel supply system in accordance with the invention may be incorporated, Fig. 2 is a lateral cross-sectional view of a fuel injection system in which the subject invention could also be applied,

Fig. 3 is a cross-sectional view as seen in the longitudinal direction of the suction channel of a fuel supply system in accordance with the invention, Fig. 4 illustrates another embodiment of the fuel supply system in accordance with the invention,

Fig. 5 is a diagram showing variations of the air-fuel ratio as a function of temperature, on the one hand with respect to a conven¬ tional carburettor and on the other with respect to a carburettor equipped with the temperature compensation feature in accordance with the invention,

Fig. 6 is a fuel supply system in accordance with Fig. 3 equipped with a special pumping device,

Fig. 7 illustrates schematically the position of choke valve arms and throttle valve arms in position of rest,

Fig. 8 is a schematical view of the positions of the arms when the engine start-up controls are engaged and the arms are hooked into one another in the so called starting position.

Description of Various Embodiments

Fig. 1 illustrates a conventional membrane carburettor in a cross-sectional view. The fuel is supplied to a fuel inlet 9 and is pumped down to a metering chamber 11. The pumping takes place in an entirely conventional way with the aid of a membrane pump driven by the engine pressure pulses in a connection 10. The metering chamber 11 is delimited downwards by a membrane 12, thus the denomination membrane carburettor. Fuel is supplied to the engine suction channel 2 by means of one or several main nozzles 3, 3'. The latter are arranged in a venturi section 13 of the suction channel 2. One or several starter nozzles 4, 4' are arranged downstream of the venturi section 13. In addition to air-regulating valves 14, 15 are arranged in the suction channel 2. In the embodiment illustrated, the valves are of rotational type but could also be of sliding type. Valve 14 is in this case a throttle valve or air throttle and 15 a choke valve. Normally, the choke valve 15 is formed with an aperture 16 allowing a small amount of air to pass through also when the valve is entirely closed. The construction of the membrane carburettor 8 so far is entirely conventional and for that reason will not be discussed in further detail.

Fig. 2 illustrates an injection system as seen in a lateral cross- sectional view. It is very similar to the membrane carburettor in Fig. 1 but is equipped with one air-regulating valve 17 only, usually called an air- throttle valve 17. In addition, it is equipped with a principal nozzle 3, 3'. Figs. 1 and 2 show examples of fuel supply systems utilizing the system in accordance with the invention. However, also similar embodiments such as a carburettor having only one air- regulating valve are conceivable, the invention being based on the through-flow resistance in each nozzle, main nozzle or starter nozzle and not on the number or types of air-regulating valves. The injection system, if any, could be without a venturi section or have a less pronounced venturi section than the one illustrated in Fig. 2. Fig. 3 is a cross-sectional view of a carburettor 8' similar to that in Fig. 1 but provided with a temperature compensation feature with respect to the fuel supply in accordance with the invention. From the metering chamber 1 1 fuel is drawn to the nozzle 3, 3'. The two nozzles 3, 3' operate in parallel and in this case they function as a principal nozzle 3, 3'. However, they could equally well function as a start-up nozzle 4, 4'. Obviously, the throttles and channel areas are in this case adjusted to the function of a start-up nozzle and not to that of a principal nozzle. A first supply channel 18 leads to a first nozzle 3 and a second supply channel 19 continues to a second nozzle 3'. Thus, the two nozzles 3, 3' are supplied with fuel in parallel. Each nozzle 3, 3' is in the shape of a metring needle valve, i.e. including a conically needle-shaped part which is movable axially in channels 24 and 25, respectively, leading away from the nozzle. Nozzle 3' is entirely con¬ ventional since its needle-shaped member is associated with a threaded portion 20 having a recess 21 for engagement by a screw¬ driver. It thus becomes possible to set the nozzle to the desired degree of throttling, which preferably is effected in connection with the manufacture and/ or the servicing of the power-driven product. The nozzle 3, on the other hand, has a movable part 5 which is secured to a temperature-responsive member 6. In turn, the latter is secured by means of a screw 23. The movable part 5 is cylindrical and axially displacable inside a hole formed in the carburettor body 8'. A seal 22, such as an O-ring, ensures that no fuel leaks from the carburettor along the movable body 5. A first outlet channel 24 leads from nozzle 3 and a second outlet channel 25 from nozzle 3'. These two channels meet and a third outlet channel 26 leads to the very suction channel 2. Outlet channel 26 is only indicated schematically. In actual fact, it is provided with a sprayer means including a check valve. Obviously, the nozzles 3, 3' and their associated outlet channels 24, 25 could also be arranged in such a manner that their respective outlet channel debouches directly in the very suction channel 2, eliminating the need for the third outlet channel 26.

The temperature compensation of the fuel supply with the aid of the temperature compensated nozzle 3 is obtained as a result of the temperature-responsive member 6, for instance a bimetal member, bending backwards at lower temperatures, as illustrated by the exag- gerated dash-and-dot line position in the drawing figure. Thus, the metering needle valve is pulled axially backwards, increasing the fuel through-flow opening and thus bringing about a reduction of the fuel through-flow resistance, admitting more fuel into the suction channel 2, i.e. a richer fuel mixture. Obviously, other temperature-responsive members than a bimetal member could be used but a bimetal mem¬ ber is advantageous, considering the resistance towards varying temperatures and different chemicals, such as oil and gasoline. The bimetal member is attached by means of a screw 23 to a side edge of the carburettor body 8'. Temperature compensation setting is effected to ensure that the temperature-responsive member 6 reaches its foremost position at a temperature of 20-30°C, preferably 25°. This is effected in that the member 6 or the movable part 5 is pushed to¬ wards an abutment face 27, in this case the member 6 is pressed towards the carburettor body side wall. Owing to the stop 27 there thus is no further increase of the fuel through-flow resistance above a certain predetermined maximum temperature, for instance 25°C. At temperatures below this limit temperature level the member 6 moves gradually further rearwards the lower the temperature becomes. In this manner the desired richer fuel mixture at lower temperatures is achieved. A rear abutment face 28 may be provided to maximize the temperature compensation at lower temperatures. Consequently, the temperature-compensated nozzle 3 lacks an adjustable basic setting but is connected so as to share fuel flow with another nozzle 3'. In this case, the nozzle 3' is adjustable in a con¬ ventional manner but it could likewise be stationary. The two nozzles thus operate in parallel. However, they could also operate in series. For instance, in that case channel 19 could be connected to the outlet from the first nozzle 3, which in that case does not debouch into the channel 26. As a result, the entire flow would first pass nozzle 3 and then nozzle 3'. The reverse order, i.e. nozzle 3' to 3 obviously is also conceivable. However, it would likewise be possible to use one single nozzle which in this case is temperature-compensated. The nozzle 3' would then be eliminated. Preferably, the temperature compensated nozzle 3 would be formed with an adjustable basic setting as a result of the movable part 5 in the nozzle being adjustably secured to the temperature dependent member 6. For instance, the nozzle may be screwed into a threaded bore in the bimetal attachment 6. Fig. 3 illustrates a membrane carburettor provided with a temperature-com¬ pensated nozzle 3 in accordance with the invention but the invention could also be used with another type of carburettor or with an injec¬ tion system as in accordance with Fig. 2. In these cases is the arrangement from the first supply channel 18 and upwards similar to that in Fig. 3 and the modifications discussed in connection there¬ with. The attachment of the movable part 5 to the bimetal member 6 could be articulated to allow for softer movements without jerks. The member could also be arranged symmetrically around its attachment to the movable part 5. When this is the case, it is attached to both sides thereof. All attachments could be of an articulated type. In all, the temperature dependent member could be configured and arranged in many different ways and be made from various materials and also be attached in a variety of different ways.

In Fig. 3 the dash-and-dot lines illustrate a temperature-trans¬ fer element 29. This means is not necessary but could be advantagous in many applications. The element could be configured in many differ¬ ent ways but in Fig. 3 it is illustrated schematically as a forked element having two sensors 30, 30'. One end of the temperature- transfer element is in heat-transfer contact with the temperature- responsive member 6, in this case by simply being screwed into its attachment in the carburettor body. Other parts of the temperature- transfer element are in heat-transfer contact with at least either the surrounding air, the engine fuel or the engine body, i.e. crank case or cylinder. The reason therefore is that the temperature of the sur¬ rounding air, of the engine fuel and of the engine all affect the engine operation and the desired air-fuel ratio. The temperature compen¬ sated nozzle may be used as a principal nozzle as well as a starter nozzle and in both cases different temperatures are of varying import¬ ance. For a starter nozzle, the engine temperature is of comparatively bigger importance than for a main nozzle but in the latter case, on the other hand, the air temperature is more important. This means that the temperature-transfer element 29 could be configured to allow for instance a metering body 30 to be positioned in its tank or in heat- transfer contact with the fuel, for instance in a wall of the fuel tank. A second metering body 30' could be attached to the crank case or cylinder in order to sense the engine temperature. The heat- transfer element proper extends in the air and, if not insulated, it thus is able to sense the temperature thereof. Depending on the application, one or several of these temperatures could be sensed and transferred to the temperature-responsive member 6. Thus the temperature-transfer element 29, if insulated with the exception of its sensor body, is able to transfer a temperature, such as the engine temperature or the fuel temperature, but also to transfer a mixture of all three relevant temperatures. The temperature transfer element 29 could for instance be a metal rod or a tube or a hose containing a liquid or pulverized material. In the absence of element 29 the temperature-responsive member 6 thus essentially senses the temperature in the carburettor body and to some extent the temperature of the surrounding air.

Fig. 4 illustrates an arrangement that differs somewhat from the nozzle illustrated in Fig. 3. The nozzle arrangement could be used both for a principal nozzle, in which case it is designated by 3, 3', or for a starter nozzle designated 4, 4'. Obviously, the dimensions of the fuel through-flow areas could be different for these two applications. The temperature compensated nozzle has a through-flow area desig¬ nated by 7 whereas the conventional nozzle, coupled in parallel, has a through-flow area designated by 7'. The through-flow areas are throttled passages in the fuel channels which in the case of the mem- brane carburettor lead from the metering chamber 11 and further to the suction channel 2 proper. This means that either two channels may lead all the way from the metering chamber to the suction channel or that a merge could be made in the same way as in Fig. 3. The temperature-compensated nozzle has a similar configuration as that illustrated in Fig. 3 but no sealing 22 is illustrated. It should be noted that the temperature-compensated nozzle 3; 4 ha s predeter¬ mined minimum through-flow size, for the purpose of allowing any dirty particles to flow past. A minimum opening of a circumferential size of approximately 70μ is suitable for this purpose. The built-in coarse filter of a carburettor normally has a mesh size of 47μ. Also the parallel nozzle 3'; 4' is designed with a predetermined minimum through-flow size, also when the nozzle occupies its innermost screwed-in position.

The dash-and-dot lines illustrate an alternative embodiment of the temperature-responsive member 6. In this case it consists of an external rod 6 the remote end of which is attached for instance to the engine body or the tank. One end of the rod is attached to the movable body 5 or a part 31 associated therewith. Part 31 in this case serves only to guide the body 5. At lower temperatures the rod 6 becomes shorter, pulling the body 5 rearwards. With respect to the temperature sensing operation the conditions referred to earlier with respect to the temperature transfer element 29 apply. The temperature-responsive member 6 could likewise be posi¬ tioned adjacent the engine body, the fuel tank or some other desirable location in order to sense the temperature suitable for the relevant application. Movement transfer from the member 6 to the body then preferably is effected with the aid of a link rod 32 or in any other suitable manner, for instance by means of a capillary tube. The move¬ ment transfer obviously could also be effected in many other ways.

Fig. 5 illustrates the variations of the air-fuel ratio as a function of temperature, with respect to a conventional carburettor and a car- burettor with the temperature compensation feature in accordance with the invention. According to the drawing figure, the fuel mixture is richer in the downwards direction and leaner upwards in the diagram and the temperature relates to the surrounding air temperature in centigrades. The conventional carburettor exhibit an approximately linear decrease of the air- fuel ratio at increasing temperatures according to the broken line. From 25°C and upwards the broken line coincides with continuous-line curve. The curve relating to a carbu¬ rettor exhibiting the temperature compensation features in accord¬ ance with the invention is shown by a continuous line. It rises approximately linearly to the highest point at approximately 25°C and thereafter it follows the curve relating to the conventional carburettor and thus decreases linearly. The break point at 25°C is due to the fact that the movable part 5 has reached its end position whereafter no further compensation is made to accommodate for higher tempera- tures. The end position is achieved by means of the stop face 27. In the absence of such a stop means the air-fuel ratio would have followed the dash-and-dot line to the right of 25°C. This situation is not desirable, since the carburettor body temperature normally becomes 20-30° higher than the surrounding temperature approximately 10- 15 minutes after shut off of the engine, for instance for fueling purposes. This would lead to a too lean setting in accordance with the dash-and-dot line, with the result that the product would be difficult to start, in addition to which it would entail risks for engine failure. Fig. 6 illustrates the manner in which the carburettor according to Fig. 1 is equipped with a particular pumping device. The latter has a suction line 50 leading via a check valve 51, 52, 53 from the car- burettor metering chamber 17 to a manually actuated pumping means 54, for instance an elastic plastic or rubber bladder. From the carburettor leads a pressure line 55 via a check valve 56, 57, 58. When the operater depresses the bladder the latter is deflated and an outlet disc 56 is forced against an outlet spring 57, whereby air and/ or fuel from the bladder 54 thus will pass the check valve and leave the pressure line 55. When the operator releases the bladder air and /or fuel is sucked from the metering chamber 1 1 to the bladder 54. This is a result of an inlet disc 51 being pressed against an inlet spring 52 in such a manner that air and /or fuel may pass the check valve. Preferably, both check valves are also provided with seals 53, 58 sealing against its respective one of discs 51, 56. Obviously, the check valves as well as the pumping means could be configured differently than described, for instance in a manner of a piston pump including membrane valves.

By repeatedly compressing and releasing the bladder the user effects pumping from the measurement chamber. The air and/ or fuel leaving the metering chamber 11 is replaced by fuel only through the normal fuel supply system of the carburettor. Owing to the pumping it thus becomes possible to remove air from the metering chamber and the latter is instead completely filled by fuel. This is evidenced by fuel only exiting from the mouth 59 of the pressure line 55. During start¬ ups there is however a risk that the metering chamber may be partly filled with air, which would make it more difficult to start the engine. By pumping away air equal conditions are created for temperature compensation at each start up. Otherwise temperature-correction of the starter nozzle at higher temperatures could make it more difficult to start the engine than without the temperature correction. This would happen in cases when air present in the metering chamber would already give the required leaner mixture. Because all air is pumped away from the metering chamber at each start-up, conditions are created to obtain a well tuned temperature correction in order to facilitate start-ups.

Figs. 7 and 8 illustrate one embodiment of the arms for actua- tion of the choke and throttle valves, not necessary for utilizing the inventive object but advantageous in connection therewith. This relates to the case when two valves are used. When only one valve is used obviously this solution is not relevant. On the lever 35 con¬ trolling the choke are mounted one choke valve arm 37 and one blocking arm 38. The blocking arm 38 is affected by a pull-back spring 39 one end of which appears in the drawing figure. The pull- back spring turns the blocking arm 38 in the counter-clockwise direction as indicated by arrows 40 to the end position illustrated in the drawing figure. With the aid of a drive shoulder 41 acting against the choke valve arm 37 the latter is carried to the shown end position. In the shown position the choke valve is fully open and the actuating rod 42 assumes its normal position, i.e. the position wherein the engine-start control lever is not affected. The start control lever is secured to the opposite end of the operating rod 42. The throttle lever 36 is non-rotationally secured to the throttle valve arm 43. A pull- back spring 44 turns the throttle valve arm 43 in the clockwise direction in the same manner as pull-back spring 39, to the end position shown. In the end position the throttle valve is fully closed. An operating lever 46 affects the throttle valve arm 43 to open the throttle valve as desired. This is the position of departure when the engine, a power saw, is not used. Fig. 8 illustrates a position of the levers when the engine is to be started. When the start control lever is engaged, the actuating rod 42 has exerted its pulling action of the choke valve arm 37 and with the aid of the drive shoulder 41 the latter has brought along the blocking arm 38 in the clockwise direction. The outer end 47 of the blocking arm 38 is formed with an indentation 48. When the outer end 47 reaches the position illustrated in Fig. 7 in dash-and-dot lines, it begins to turn the throttle valve arm 43 in the counter-clockwise direction. This continues until an abutment face 49 formed at one end of the throttle valve arm rides across the edge of the outer end 47 and reaches the indentation 48. The path of movement of the start control lever is adjusted to ensure that the arms 37, 38 and 43 reach precisely the desired position illustrated in Fig. 8. In this position a full-choke condition is reached while at the same time the throttle valve is slightly opened. This small opening of the throttle valve corresponds to the desired start throttle condition. As soon as the engine starts the start control lever may be pushed inwards. This turns the choke valve arm 37 whereas the blocking arm 38 still is hooked in the throttle valve arm 43. When the operator opens the throttle, the actuating rod 46 will turn the throttle valve arm 43 in the counter-clockwise direction, thus unhooking the blocking arm 38 and the latter returns to the position illustrated in Fig. 7. The arrangement in accordance with Figs. 7 and 8 has several advantages. Firstly, a suitable start throttle condition is provided when the start control lever is pulled outwards. In the hooked condition the actuating rod 42 is not affected by spring action from the pull back spring 39. This allows the start control lever to be pushed inwards slowly after start. On the other hand, when the throttle is opened, the blocking arm 38 is liberated and the start control lever may be pulled back. Secondly, the arrangement provides definite positions of the choke and throttle valves and these positions are repeated upon each starting instance. This is an important condition for obtaining a well tuned temperature correction for easier start-ups.

Claims

1. A fuel supply system (1) for an internal combustion engine, arranged in a suction channel (2) leading to the very engine body, said system (1) comprising one or several nozzles (3, 3'; 4, 4' ), charac- t e r i z e d in that at least one nozzle (3; 4) is configured in such a manner that its fuel through-flow resistance changes upon tempera¬ ture changes as a result of a movable part (5) in the nozzle being connected to a temperature-responsive member (6), directly or via an intermediary member (32), such as a bimetal member (6), a memory metal member (6), or an external rod (6), whereby the movable part (5), upon lower temperature levels, is moved by the member (6) for reduction of the fuel through-flow resistance, usually by an increase of the fuel through-flow opening (7), and thus the fuel through-flow is increased and a richer fuel mixture is obtained, i.e. a temperature compensation of the fuel supply with the aid of a temperature- com- pensated nozzle (3; 4).

2. A fuel supply system as claimed in claim 1, c h a r a c ¬ t e r i z e d in that at a certain temperature, preferably 20-30°C and preferably 25°C, the movable part (5) reaches an end position as its movement is limited by a stop means (27), whereby the fuel through-flow resistance does not increase further above said temperature.

3. A fuel supply system according to claim lor2, c h a r ¬ a c t e r i z e d in that the temperature-compensated nozzle (3; 4) is designed in such a manner that its basic setting is adjustable owing to the adjustable attachment of the movable part (5) of the nozzle in the temperature-responsive member (6), for instance by said nozzle being screwed in a threaded means in a bimetal attachment.

4. A fuel supply system according claim lor2, c h a r ¬ a c t e r i z e d in that the temperature-compensated nozzle (3; 4) does not have an adjustable basic setting but is connected so as to cooperate with another nozzle (3'; 4^ which is stationary or adjust¬ able, such that both nozzles operate in parallel or in series.

5. A fuel supply system according to any one of the preceding claims, c h a r a c te r i z e d in that the temperature-compen- sated nozzle (3; 4) has a predetermined minimum through-flow size.

6. A fuel supply system accoding to any one of the preceding claims, c h a r a c te r i z e d in that the temperature-compen¬ sated nozzle (3), alone or in combination with another nozzle (3"), is used as the main nozzle (3, 3^*).

7. A fuel supply system according to any one of the preceding claims, c h a r a c t e r iz e d in that the temperature -compen¬ sated nozzle (4), alone or in combination wiht another nozzle (4, 4"), is used as a starter nozzle (4, 4^*).

8. A fuel supply system according to any one of the preceding claims, c h a r a c t e r i z e d in that a temperature-transfer element (29), for instance a metal rod or a tube or a hose containing a liquid or pulverized material, has heat transfer contact at one of its ends with the temperature-responsive member (6) whereas other parts of the temperature-transfer element (29) are in heat transfer contact with at least either the surrounding air, the engine fuel or the engine body, i.e. crank case or cylinder.

9. A fuel supply system (1) according to any one of the preced¬ ing claims, c h a r a c t e r i z e d in that the fuel supply system is of membrane carburettor type.

10. A fuel supply system (1) according to claim 9, c h a r ¬ a c t e r i s e d in that a pumping device (50-58) having a suction line (50) connected to the metering chamber (11) of the carburettor, is arranged adjacent the carburettor and that upon pump operations air and/ or fuel is pumped from the metering chamber.

11. A fuel supply system (1) according to any one of the preced¬ ing claims, c h a r ac te ri z e d in that the system comprises two air-regulating valves (14, 15,), viz. a choke valve (15) and a throttle valve (14), said choke valve being non-rotationally secured to a choke control lever (35) and the throttle valve being non-rotationally secured to a throttle lever (36), said choke control lever (35) carrying a non-rotationally mounted choke valve arm (37) and a rotationally mounted blocking arm (38), the latter being provided with a drive shoulder (41) arranged to drive the choke valve arm (37) in a direction towards closing of the choke valve (5), and a biased check spring (39) arranged in such a manner as to turn the blocking arm (38) and thus also the choke valve arm (37) to close the choke valve, and a rotary movement of the choke valve arm (37) from the closed position causing a rotational movement also of the blocking arm (38), the outer end (47) of which cooperates with the throttle valve arm (43), turning the latter from its normally closed position, and the blocking arm (38) and throttle valve arm being provided with cooperating hook members (48, 49) arranged to interlock in a position of full choke of the choke valve (5) and an adjusted start throttle condition of the throttle valve (6), said hooking members being for instance an indentation (48) formed at the outer end (47) of the blocking arm (38) to cooperate with an abutment means (49) at one end of the throttle valve arm.