Internally vented float bowl primer arrangement

A manually actuable primer for an internally vented float regulated fuel bowl type carburetor employs an arrangement for minimizing variations in fuel mixture richness resulting from variations in air intake path restrictions as might be created by a clogged air filter includes a bifurcated float bowl air vent conduit with one branch communicating with the carburetor bore in the region of the Venturi and the other branch communicating with the bore outside the region of the Venturi along with an arrangement for directing displaced fuel from the fuel supply chamber directly into a conduit which normally conveys fuel from a fuel well to the Venturi region, the directing arrangement being formed as an annular insert for the fuel well, the aperture of which forms the fixed fuel metering orifice of the carburetor. With this arrangement primer actuation pressurizes the region above the fuel in the float bowl, forcing fuel through the annular member directly into the nozzle communicating between the fuel well and the carburetor bore Venturi, while the bifurcated float bowl air vent arrangement allows a smaller vent opening into the float bowl, making float bowl pressurization priming feasible, while minimizing mixture richness changes normally associated with air intake obstructions such as a dirty air filter.

BACKGROUND OF THE INVENTION 
The present invention relates generally to carburetion systems for internal 
combustion engines and more particularly to a single control fixed fuel 
metering internally vented float bowl carburetor with enhanced priming 
capacity. 
Small engine carburetors may be categorized as either of the diaphragm type 
where pressure differentials move a diaphragm to control fuel flow to the 
carburetor or of the float bowl type where a valve controlling float opens 
and closes to maintain a preferred fuel level in a fuel reservoir or 
chamber within the carburetor. 
In one version of the float bowl type carburetor, fuel flows from this 
reservoir through a fuel metering orifice into a fuel well from which that 
fuel is sucked up and mixed with air due to the pressure differential 
caused by a Venturi region in the carburetor bore or throat. A proper fuel 
flow rate in this variety of carburetor is facilitated by venting the top 
of the float bowl to a constant pressure region. This venting may be to 
the atmosphere external of the carburetor or to a region of relatively 
constant pressure close to atmospheric pressure within the carburetor 
bore. The latter scheme is referred to as internal venting and has the 
advantage that the air supplied to the vent has already passed through the 
carburetor air filter and the likelihood that dirt will be introduced into 
the system causing difficulties such as the clogging of the fuel metering 
orifice is reduced. 
Over a period of time, the engine intake air filter becomes dirty and 
clogged, so as to restrict air intake into the engine and to create a 
pressure drop across that air filter. With an externally vented float 
bowl, the effect of this restriction is to cause the engine to run on fuel 
rich mixture with the typical symptoms of loss of power, excessive carbon 
build-up in the combustion chamber and fouled spark plugs. The mixture 
becomes excessively rich because the pressure in the float bowl, forcing 
fuel through the metering orifice, remains at atmospheric pressure, so the 
rate at which fuel is supplied to the engine remains relatively fixed 
while the air intake restriction reduces the amount of air drawn into the 
engine, creating the unduly rich situation. 
In an internally vented float bowl carburetor, the result of air intake 
restriction is to reduce the pressure within the float bowl and diminish 
the rate at which fuel is supplied to the engine with this effect being 
somewhat more pronounced than the decrease in combustion air being 
supplied to that engine so that the net result is an unduly lean mixture 
being supplied to the engine with the typical system of overheating of the 
engine. The smaller the air vent opening into the float bowl becomes, the 
more pronounced this leaning out effect due to air intake restriction 
becomes. 
It is common practice to supply an initially fuel rich mixture to an 
internal combustion engine when attempting to start that engine. In 
addition to the conventional choke valve, several schemes for squirting 
fuel into the throat of the carburetor have been devised. An automatic 
arrangement for accomplishing this initial priming function is illustrated 
in U.S. Pat. No. 3,780,996 wherein when the engine is not running, a 
relatively small fuel well is filled to a certain level from the float 
bowl by way of the fuel metering orifice and when the engine is initially 
cranked, part of the fuel in this fuel well is forced into the carburetor 
throat and thereafter the engine runs with the fuel level in the well 
substantially lower than that fuel level was prior to initially cranking 
the engine. This system provides a fixed priming charge and works well so 
long as the environmental temperature range in which the engine is to be 
used is not excessive. For example, such an automatic priming scheme is 
well suited to lawnmower engine installations since the range of 
temperatures over which the average individual will mow a lawn is fairly 
limited. This patented system employed a single manual control member and 
a single fuel supply nozzle in conjunction with a fixed fuel metering 
orifice and represents a very simplistic and economical carburetion 
system. On the other hand, this patented system is certainly limited in 
the range of temperatures in which it may be employed and requires a short 
waiting period between attempts to start the engine in order to allow time 
for fuel to again fill the fuel well. 
An improvement on the aforementioned U.S. Pat. No. 3,780,996 is illustrated 
in U.S. Pat. No. 4,203,405 wherein the advantages of the earlier patented 
device are retained while adding the capability of manual priming of the 
system. In this improvement, a flexible primer bulb may be depressed to 
increase the pressure on the surface of the fuel within the fuel well, 
forcing that fuel upwardly through a nozzle tube and into the throat of 
the carburetor. This later patented system may be operated in an automatic 
prime mode as with the earlier patented system, or preparatory to 
starting, the primer bulb may be depressed, forcing a first charge of fuel 
into the carburetor throat, and then, depending upon the time between 
primer actuation and starter actuation, a second at least partial fuel 
charge is introduced by the automatic priming aspect when the engine is 
cranked. Both of these patented systems require a time lag between priming 
attempts in order to allow time for fuel to re-enter the fuel well through 
the metering orifice. Thus, the priming capacity of this later patented 
device remains somewhat more limited than desired. 
SUMMARY OF THE INVENTION 
Among the several objects of the present invention may be noted the 
provision of an internally vented float bowl carburetor having a 
relatively constant fuel mixture richness despite air intake restriction 
variations, as might for example be created by a dirty-clogged air filter; 
the provision of an operator actuable fuel primer of increased capacity; 
the provision of an operator actuable fuel primer requiring substantially 
no waiting period between successive actuations; the provision of a 
carburetor which automatically provides a small priming fuel charge to an 
engine when that engine is cranked and is capable of providing repeated 
additional priming charges upon manual actuation of a primer bulb; and the 
provision of an internally vented float bowl type carburetor having a 
substantially reduced size vent opening into the float bowl. These as well 
as other objects and advantageous features of the present invention will 
be in part apparent and in part pointed out hereinafter. 
In general and in one form of the invention, the entire region above the 
fuel in the float bowl is pressurized upon actuation of a primer bulb. The 
bowl vent opening is reduced substantially as compared to prior venting 
arrangements so that this pressurization may occur. The fuel-air mixture 
problems which might otherwise be accentuated by this small bowl vent 
opening are compensated for by connecting the bowl vent opening to the 
Venturi region of the carburetor bore as well as to a region outside the 
Venturi region. The effectiveness of the primer operation is enhanced by 
providing an annular insert which functions both as the fuel metering 
orifice and upon primer actuation functions to direct the prime charge 
upwardly through the tube leading from the fuel well to the carburetor 
throat. 
Also in general and in one form of the invention, a single control fixed 
fuel metering carburetor for providing a combustible fuel air mixture 
through the bore thereof to a conventionally aspirated internal combustion 
engine has a restricted Venturi region along with a float regulated fuel 
supply chamber and a fuel well which is gravity fed from the float 
regulated chamber along with a conduit arrangement for conveying fuel from 
the fuel well to air passing through the carburetor bore in the region of 
the Venturi. A bifurcated fuel supply chamber air vent conduit with one 
branch thereof communicating with the bore in the region of the Venturi 
and another branch thereof communicating with the bore outside the region 
of the Venturi maintains the air pressure within the chamber relatively 
constant despite variations in restricting the amount of air entering the 
carburetor. The fuel flow metering orifice may be aligned with this 
conduit and a manually actuable primer employed to increase the air 
pressure within the fuel supply chamber thereby displacing fuel from that 
chamber through the fuel flow metering orifice and directly into the 
conduit.

Corresponding reference characters indicate corresponding parts throughout 
the several views of the drawing. 
The exemplifications set out herein illustrate a preferred embodiment of 
the invention in one form thereof and such exemplifications are not to be 
construed as limiting the scope of the disclosure or the scope of the 
invention in any manner. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in general, a carburetor 11 provides a 
combustible fuel air mixture to a conventionally aspirated internal 
combustion engine having, for example, flange 13 bolted either directly to 
the engine or to an intake manifold thereof. Air is supplied to the 
carburetor through an air filter which attaches to surface 15 on the air 
inlet side of the carburetor. Air flows through the carburetor in the 
direction illustrated by the arrows in FIG. 1. The carburetor has a single 
control in the form of a conventional butterfly valve attached to rod 17 
and movable by actuating arm 19 between positions where the carburetor 
bore 21 is nearly closed and where that bore is substantially unobstructed 
by the butterfly valve. This valve constitutes the sole variable air 
restrictor in the carburetor bore. Fuel metering for the carburetor is 
also fixed by the size of the aperture through the annular insert 23 with 
this opening constituting the fuel metering orifice of the carburetor. 
Referring primarily to FIG. 2, the carburetor has a float regulated fuel 
supply chamber 25 of conventional construction with an annular float 27 
pivoted at 29 and controlling needle 31 with respect to seat 33 to open 
the valve defined by the needle and seat and allow fuel to enter the float 
regulated chamber or bowl 25 when the level of that fuel drops 
sufficiently to open the valve. Thus, fuel is supplied to the carburetor 
by way of a fuel line attached to fitting 35. 
Fuel in the fuel supply chamber 25 passes through openings, such as 37 and 
39, into region 41 and then upwardly through the annular insert 23 into a 
fuel well 41 to thereafter be aspirated by way of nozzle tube 43 into the 
Venturi region of the carburetor bore during normal engine operation. Fuel 
well 41 is thus gravity fed from the float regulated chamber 25 with 
nozzle tube 43 constituting a conduit for conveying fuel from the well 41 
to air passing through the carburetor and into the engine during normal 
engine operation. 
An air filled variable volume chamber 45 of FIG. 1 is actuable by an 
operator by depressing the pliable dome 47 from its normal position to the 
position of the pliable dome 47 illustrated to abruptly displace a 
discrete volume of air from that variable volume chamber by way of hose 49 
and fitting 51 through opening 53 and into region 55 in the fuel supply 
chamber 25. Thus, tube 49 and fitting 51 along with opening 53 form a part 
of a passageway interconnecting the variable volume chamber 45 to the fuel 
supply chamber 25 with a decrease in the volume of the variable volume 
chamber 45 forcing air into the fuel supply chamber 25. This air 
displacement in turn displaces fuel from the fuel supply chamber 25 by way 
of openings 37 and 39 upwardly through the orifice of annular insert 23 so 
that the fuel is directly aligned with or guided into nozzle 43 to squirt 
upwardly into the carburetor bore or throat. The annular insert 23 is 
located within fuel well 41 displaced from and axially aligned with the 
conduit 43 so as to direct the displaced fuel from the fuel supply chamber 
25 directly into the cylindrical nozzle 43. 
Air flow through the carburetor throat is from right to left, as 
illustrated by the arrows in FIGS. 1 and 3, with that air flowing 
initially into the carburetor bore 57 and continuing into the restricted 
Venturi region 59 where the pressure differential between regions 59 and 
57 forces fuel mixed with air upwardly through nozzle 43 to be mixed with 
the air flowing through the carburetor bore and pass into the engine. 
To minimize variations in fuel mixture richness resulting from variations 
in air intake path restrictions, such as a buildup of dirt in the air 
filter, an internal venting effect into the Venturi is provided which acts 
as a balancing or stabilizing factor minimizing these variations. This 
internal venting of the float bowl into the Venturi region is provided by 
a bifurcated float bowl air vent conduit having three branches, as perhaps 
best seen in FIG. 3. One branch 61 communicates with the carburetor bore 
in the Venturi region 59, while another branch 63 communicates with the 
bore outside the region of the Venturi. Thus, there is the normal Venturi 
induced pressure differential between these two outlets. The third branch 
is a small hole 65 extending from the hole 63 directly downwardly and 
opening into the upper region of the float bowl, as illustrated in FIG. 4. 
This air vent conduit then is seen to comprise three generally cylindrical 
holes formed in the body portion of the carburetor with hole 63 being the 
first and larger of the holes and being formed as a blind hole opening 
into the carburetor bore 57 outside the Venturi region. The hole 61 is the 
second and next largest of these cylindrical holes and also constitutes a 
blind hole extending transverse to and intersecting the first hole 63 
while opening into the Venturi region 59 of the bore. In practice, hole 61 
is drilled into the carburetor body portion and then plugged by ball 67 so 
as to form a blind hole. Hole 65 which opens into the carburetor float 
bowl is the smallest of the three holes and extends from an upper surface 
of the fuel supply chamber so as to intersect the first hole 63. 
In order that actuation of the primer bulb 47 will force a priming charge 
of fuel into the carburetor bore, hole 65 must be relatively small, and by 
way of illustration this hole was in one embodiment of the present 
invention about 24/1000ths of an inch in diameter. The fuel metering 
aperture in annular member 23 was about the same size as the opening of 
the air vent conduit 65 into the fuel supply chamber while the diameter of 
the Venturi region conduit opening was half again the diameter of the 
float bowl opening, and the diameter of the bore opening 63 was on the 
order of four times the diameter of the float bowl opening. With these 
dimensions, adequate priming and minimum mixture richness variations were 
obtained. 
A preferred embodiment of the invention as above described was otherwise 
constructed and functions much the same as the carburetor described in the 
aforementioned U.S. Pat. Nos. 3,780,996 and 4,203,405 to which reference 
may be had for additional conventional details of the carburetor. 
From the foregoing it is now apparent that a novel process for supplying a 
priming charge of fuel to an internal combustion engine as well as a novel 
arrangement for venting the float bowl so as to minimize mixture richness 
variations has been disclosed meeting the objects and advantageous 
features set out hereinbefore as well as others and that modifications as 
to the precise configurations, shapes and details may be made by those 
having ordinary skill in the art without departing from the spirit of the 
invention or the scope thereof as set out by the claims which follow.