Starting system for diaphragm carburetor

The object of the present invention is to easily provide an appropriate amount of starting fuel for all-purpose engines, without requiring any special skill. The upstream side and downstream side of a throttle valve in an air intake passage are connected by a bypass. This bypass and a constant-fuel chamber are connected by an increased-fuel passage which is equipped with a check valve. The system is arranged so that the bypass and increased-fuel passage are opened and closed more or less simultaneously by an opening-and-closing valve. The necessary amount of starting fuel can be supplied to the engine in a short time by means of the increased-fuel passage, so that starting can be accomplished by cranking the engine a few times. The flow of air into the constant-fuel chamber from the bypass is prevented by the check valve so that rough idling and the need to expel inflowing air are eliminated; and starting operations may be performed in any desired order.

FIELD OF THE INVENTION 
The field of the present invention is diaphragm-type carburetors and 
associated devices used to supply fuel to all-purpose two-cycle engines, 
where the devices supply an extra amount of fuel to improve 
low-temperature starting characteristics. 
BACKGROUND OF THE INVENTION 
In most all-purpose two-cycle engines used as a power source in small 
vehicles and working machinery for agriculture and forestry, etc., fuel is 
supplied by means of a diaphragm type carburetor equipped with a 
constant-fuel chamber. The constant-fuel chamber is separated from the 
atmosphere by a diaphragm which adjusts fuel introduced from a fuel pump 
to a constant pressure, and feeds the fuel into the air intake passage. 
In such diaphragm type carburetors, a means (generally a manual starting 
pump) for feeding out an extra amount of fuel into the air intake passage 
prior to the starting of the engine or for introducing a prescribed amount 
of fuel into the constant-fuel chamber, is provided in addition to the 
ordinary main fuel system and low-speed fuel system. The extra fuel thus 
provided improves the starting characteristics of the engine at low 
temperatures. 
Carburetors equipped with such starting pumps typically include 
suction-type carburetors in which the action of the starting pump causes 
the fuel to flow from the fuel tank, through the fuel pump, into the 
constant-fuel chamber (or air intake passage), and finally to the starting 
pump. An example of a suction-type carburator is described in Japanese 
Patent Application Kokai No. Sho 55-69748), herein incorporated by 
reference. Push type carburetors operate by pushing the fuel from the fuel 
tank to the starting pump, into the fuel pump, and then to the 
constant-fuel chamber (or outside overflow). An example of such a system 
as seen in Japanese Patent Application Kokai No. Sho 47-38218, is 
incorporated herein by reference. 
When the engine is cranked with starting fuel collected in the air intake 
passage or constant-fuel chamber as described above, the starting fuel 
flows toward the engine as a result of the negative pressure of the intake 
air. However, at low temperatures, the evaporization of the fuel is 
difficult and this flow becomes liquid flow. The liquid flow is propagated 
along the walls of the air intake passage or the walls of the intake 
manifold requiring a large quantity of starting fuel, especially at 
extremely low temperatures. 
One conceivable method of dealing with this problem in a carburetor in 
which starting fuel is caused to flow out and collect in the air intake 
passage is to vary the number of times that the starting pump is operated 
depending on the engine temperature. However, a high degree of precision 
is required to cause an appropriate amount of starting fuel to flow out 
and collect in the air intake passage; accordingly, such a method is not 
generally practical. Also, another problem for systems in which starting 
fuel is accumulated and held in the constant-fuel chamber is the extremely 
small diameters of the idle port and main nozzle which cause the fuel to 
be sucked out into the air intake passage by the negative pressure of the 
intake air. As a result, the necessary amount of starting fuel cannot be 
supplied to the engine unless cranking is repeated numerous times. 
The present invention solves the abovementioned problems encountered in 
conventional starting fuel supplying means in which cranking is performed 
after a starting pump is operated to improve cold starting performance by 
accumulation starting fuel in the air intake passage or constant-fuel 
chamber. In particular, the present invention solves the difficulty of 
maintaining an appropriate amount of starting fuel in the air intake 
passage, and prevents the need to perform cranking numerous times in order 
to suck the necessary amount of starting fuel out of the constant-fuel 
chamber. The present invention provides an easy-to-operate starting fuel 
supply device which makes it possible to supply the necessary amount of 
starting fuel held in the constant-fuel chamber to the engine in a short 
time so that low-temperature starting can be easily and reliably 
accomplished without the need for any particular skill. 
SUMMARY OF THE INVENTION 
Specifically, the present invention is constructed so that the upstream 
side and downstream side of a throttle valve installed in an air intake 
passage are connected by a bypass, fuel in a constant-fuel chamber is 
caused to flow out into the bypass by means of an increased-fuel passage, 
the aforementioned bypass and increased-fuel passage are caused to open 
and close more or less simultaneously by means of a manual 
opening-and-closing valve, and a check valve is installed in the 
increased-fuel passage to prevent the flow of air into the constant-fuel 
chamber from the bypass. 
The starting fuel introduced into the constant-fuel chamber by the starting 
pump is sucked out and supplied to the engine by the negative pressure 
generated in the bypass when cranking is performed with the 
opening-and-closing valve open. Since the increased-fuel passage is a 
separate system from the main fuel system and low-speed fuel system, the 
effective diameter of the increased-fuel passage can be set as desired, 
making it possible to supply the required amount of starting fuel in a 
short time so that starting can be accomplished with little cranking. 
As a result of the installation of the check valve one can avoid the 
problem of being unable to introduce starting fuel because of air being 
sucked into the constant-fuel chamber from the bypass when the 
opening-and-closing valve is opened before or during the operation of the 
starting pump. In suction type systems the inconvenient procedure 
requiring operation of the starting pump to expel air which is sucked in 
during cranking is also made unnecessary by use of the check valve, making 
it possible to achieve easy operation with no need for any special skill.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A working configuration of the present invention will be described with 
reference to the attached figures. In FIG. 1, a fuel pump 7 and a 
constant-fuel chamber 12 are installed on the outside of a carburetor main 
body 1 containing an air intake passage 5 in which a choke valve 2, 
venturi 3 and throttle valve 4 are installed in that order from the intake 
opening toward the outlet opening. 
In its preferred embodiment, the fuel pump 7 is a well-known diaphragm type 
fuel pump. The diaphragm is caused to pulsate by the introduction of the 
pulse pressure generated in the crankcase of the engine via a pulse 
pressure introduction tube 8, so that fuel from the fuel tank 10 is sucked 
in and pressurized via a fuel introduction tube 9, and is then fed into 
the constant-fuel chamber 12 via a fuel passage 11. 
The constant-fuel chamber 12 is separated by a diaphragm 13 from an 
atmosphere chamber 15 located inside a diaphragm cover 14. A fuel valve 18 
is engaged with a lever 17 which is caused to contact the center of the 
diaphragm 13 by the force of a spring 16. The fuel valve 18 opens and 
closes the fuel passage 11 in accordance with the displacement of the 
diaphragm 13 so that a prescribed amount of fuel is held at a constant 
pressure. Then, the fuel in this constant-fuel chamber 12 is sucked out 
into the air intake passage 5 via a main nozzle 19 which opens into the 
narrowest part of the venturi 3 and idle and slow ports (not shown in the 
figures) which open to one side of the throttle valve 4. 
A common finger-pressed dome type starting pump 23 is installed on the 
outside surface of the carburetor main body 1 alongside the fuel pump 7. A 
suction passage 24 extending from the constant-fuel chamber 12 connects to 
the intake opening of the starting pump 23, and a discharge passage 25 
connects to a discharge opening of the starting pump 23 and leads to the 
fuel tank 10. 
In cases where the engine is stopped with the constant-fuel chamber 12 
empty of fuel, or in cases where the engine stops as a result of running 
out of fuel, the starting pump 23 is operated by hand prior to the next 
operation of the engine, so that fuel from the fuel tank 10 is supplied to 
the constant-fuel chamber 12 by suction via the fuel introduction tube 9, 
fuel pump 7 and fuel passage 11. When the engine is to be started at low 
temperatures, the starting pump 23 is further operated so that a 
prescribed amount of fuel, i.e., the amount of fuel required for starting, 
is introduced into the constant-fuel chamber 12. 
After the constant-fuel chamber 12 is filled with fuel, fuel will flow 
through the suction passage 24, starting pump 23 and discharge passage 25. 
In a preferred embodiment, the accumulation of a sufficient amount of 
starting fuel can be appropriately confirmed by making at least the 
portions of the suction passage 24 and discharge passage 25 located in the 
vicinity of the starting pump 23 transparent. 
A bypass 31 which extends parallel to the air intake passage 5 from the end 
surface on the intake side of the carburetor main body 1, and which opens 
into the air intake passage 5 at a point downstream from the throttle 
valve 4, is formed in the carburetor main body 1, so that air from an air 
cleaner (not shown in the figures) can be supplied to a point located 
downstream from the throttle valve 4 without passing through the choke 
valve 2, venturi 3 and throttle valve 4. 
As best seen in FIGS. 1 and FIG. 2, an increased-fuel passage 32 which 
connects the constant-fuel chamber 12 and the bypass 31 is also provided 
via preferred embodiment. This increased-fuel passage 32 is installed at 
right angles to the bypass 31, and comprises a check valve 33 which has a 
flat plate-form valve body 33b and a valve seat 33a installed in the 
intake end portion which opens into the constant-fuel chamber 12, (ii) a 
suction port 35 which opens at the center of a seating surface 34 formed 
in a location that is slightly withdrawn from the circumferential wall 
surface of the bypass 31, and (iii) a metering jet 36 which is formed 
between the abovementioned check valve 33 and suction port 35. 
Additionally, a guide hole 38 is positioned on the same central axial line 
as the increased-fuel passage 32, the guide hole 38 having a diameter 
slightly larger than that of the bypass 31. The guide hole 38 is formed so 
that it cuts across the bypass 31 at right angles from the area 
surrounding the seating surface 34, and opens at the outside surface of 
the carburetor main body 1. A plunger-form valve body 41 is inserted into 
the guide hole 38. A plate-form sealing member 42 made of an elastic 
material which will adhere tightly to the seating surface 34 is fastened 
to the tip end surface of the valve body 41, and an O-ring 43 which closes 
the gap between the valve body 41 and the walls of the guide hole 38 is 
mounted on the outer circumferential surface of the valve body 41. A valve 
shaft 44 extends from the base end surface of the valve body 41, the valve 
shaft 44 having the same diameter as the valve body 41. At the tip end of 
said valve shaft 44 is an annular anchoring groove 45 which is formed at 
the base end surface of the valve body 41 and an inclined surface of the 
valve shaft 44. The anchoring groove 45 causes the diameter of the valve 
shaft 44 to decrease toward the tip end. The valve shaft 44 has a knob 46 
located on the base end of said valve shaft 44, which protrudes to the 
outside of the carburetor main body 1. 
An annular retaining groove 48 is formed in an eccentric manner in a 
tubular protrusion 47 which protrudes from the carburetor main body 1 so 
that the tubular protrusion 47 surrounds the guide hole 38. A portion of 
this retaining groove 48 opens into the guide hole 38. Furthermore, a 
stopper 49 consisting of a split-ring spring is mounted and held in the 
retaining groove 48 with one portion of the stopper 49 contacting the 
outer circumferential surface of the valve shaft 44. 
The abovementioned seating surface 34, valve body 41, valve shaft 44 and 
knob 46 constitute a manual opening-and-closing valve 40. In the state 
shown in FIG. 2, in which the valve body 41 is pushed deeply into the 
guide hole 38 so that the sealing member 42 is caused to adhere tightly to 
the seating surface 34, the opening-and-closing valve 40 closes both the 
bypass 31 and the increased-fuel passage 32. When the valve body 41 is 
pulled by means of the knob 46, the bypass 31 and increased-fuel passage 
32 are opened more or less simultaneously, and the bypass 31 is fully 
opened in the state shown in FIG. 3, in which the stopper is caused to 
enter the anchoring groove 45 by the elastic force of the stopper 49. 
In cases where the engine is started at ordinary or high temperatures, 
starting can be accomplished by means of fuel from the existing fuel 
system, accordingly, the opening-and-closing valve 40 may remain closed. 
When the engine is to be started at low temperatures, the starting pump 23 
is operated as described above so that a prescribed amount of fuel is 
introduced into the constant-fuel chamber 12; then, the 
opening-and-closing valve 40 is generally pulled to the fully open 
position shown in FIG. 3. With the constant-fuel chamber 12 in a full 
state, the engine can then be cranked. As a result of this cranking, air 
flows through the bypass 31 so that the fuel in the constant-fuel chamber 
12 is sucked out into the bypass 31 from the suction port 35 (while being 
metered by the metering jet 36 with the check valve 33 open) by the 
negative pressure acting on the suction port 35, and this fuel is supplied 
to the engine. 
Cranking causes air to flow through the air intake passage 5, so that fuel 
is sucked out from the main nozzle 19 when the idle port and choke valve 2 
are closed. In this case, it is possible to cause a large amount of fuel 
to be sucked out into the bypass 31 by appropriately setting the effective 
diameter of the metering jet 36. Accordingly, even at extremely low 
temperatures, the necessary amount of starting fuel can be supplied to the 
engine in a short time, so that starting with complete combustion can be 
accomplished by cranking the engine a few times. 
When starting the engine, persons inexperienced in the handling of engines 
may operate the starting pump 23 after opening the opening-and-closing 
valve 40 without following the abovementioned procedure, or may open the 
opening-and-closing valve 40 at an intermediate point during the operation 
of the starting pump 23. In such cases, the constant-fuel chamber 12 on 
the intake side of the starting pump 23 is placed under negative pressure, 
so that air begins to be sucked in from the bypass 31 via the 
increased-fuel passage 32. However, the check valve 33 is closed so that 
this suction of air is prevented. Thus, the difficulty in introducing 
starting fuel into the constant-fuel chamber 12 against the continued 
suction of air by the starting pump 23 tends to be prevented. 
Accordingly, the operating procedure during starting may be performed as 
desired so that the device is extremely easy to operate for experienced 
and inexperienced persons alike. 
When the engine has completely fired, the opening-and-closing valve 40 is 
returned to the closed position at an appropriate time, so that engine 
operation subsequently continues supplied with fuel from the main fuel 
system or low-speed fuel system that is sucked out into the air intake 
passage 5. 
When the opening-and-closing valve 40 is returned to the closed position, 
the air sealed inside the increased-fuel passage 32 and the guide hole 38 
attempts to enter the constant-fuel chamber 12; however, because the check 
valve 33 closes at the same time that the sealed-in air begins to be 
compressed, the flow of air into the constant-fuel chamber 12 will tend to 
be prevented. Accordingly, the problem of unstable idling or stopping of 
the engine due to the temporary feeding of fuel into the air intake 
passage 5 from the main fuel system or low-speed fuel system tends to be 
eliminated. 
As a result of the above, a transition from idling based on a rich mixture 
during low-temperature starting with the opening-and-closing valve 40 in 
an open state to idling based on an ordinary mixture with the 
opening-and-closing valve 40 in a closed state can be accomplished without 
any stopping of the engine or great drop in engine revolution, so that 
starting of the engine at low temperatures can be accomplished in a stable 
and reliable manner. 
Furthermore, in cases where the engine is stopped with the 
opening-and-closing valve 40 in an open state, the diaphragm 13 which 
forms the constant-fuel chamber 12 is caused to return from a fixed 
position, i.e., a position in which the diaphragm is displaced toward the 
constant-fuel chamber 12 by the suction negative pressure and suction of 
fuel, to the pre-starting position by the force of the spring 16. Also, 
the check valve 33 closes so that the suction of air into the 
constant-fuel chamber 12 from the bypass 31 tends to be prevented. 
Accordingly, there usually no need to expel sucked-in air by operating the 
starting pump 23 during restarting. 
The present invention was described above with reference to the system 
illustrated in the figures, in which fuel is sucked into the constant-fuel 
chamber 12 by the starting pump 23, however, it would also of course be 
possible to apply the present invention to a system in which fuel is 
pushed into the constant-fuel chamber 12. 
As was described above, the use of the present invention, in which a bypass 
31 is installed in the air intake passage 5, and fuel from a constant-fuel 
chamber 12 is sucked out into the bypass 31 via an increased-fuel passage 
32 equipped with a check valve 42 in synchronization with the opening and 
closing of the bypass 31 so that fuel for low-temperature starting can be 
obtained, allows arbitrary setting of the effective diameter of the 
increased-fuel passage 32. The increased-fuel passage is a separate system 
from the main fuel system and low-speed fuel system, so that the necessary 
amount of starting fuel can be supplied to the engine in a short time, 
making it possible to start the engine by cranking the engine only a few 
times. 
Furthermore, since the flow of air into the constant-fuel chamber 12 from 
the bypass 31 is prevented by a check valve 42, the order in which the 
opening operation of the opening-and-closing valve 40 and the operation of 
the starting pump 23 are performed is unimportant. Accordingly, the 
following merits are also obtained: the device is convenient to use, there 
is usually no need to operate the starting pump 23 in order to expel air 
that may have flowed into the constant fuel chamber 12, and operation of 
the device is easy with no need for any special skill. 
While the above description contains many specifics, these should not be 
construed as limitations on the scope of the invention, but rather as 
examples of particular embodiments thereof. Many other variations are 
possible. Accordingly, the scope of the present invention should be 
determined not by the embodiments described herein, but by the appended 
claims and their legal equivalents.