Marvel-Schebler Carbureter
Contents
1. RI 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM Marvel Schebler Carbureter Marvel Schebler Carbureters are used on thousands of tractor and industrial engines and have been designed to provide many years of trouble free service however as in the case of all mechanical devices they do in time require roper service and repairs An understanding of their construction and how they operate as well as an understanding of their function with respect to the engine will not only avoid many false leads on the part of the service man in diag nosing so called carbureter complaints but will create customer satisfaction and a profitable business for the progressive service shop To understand a carbureter it is necessary to realize that there is only one thing that a carbur eter is designed to do and that is to mix fuel and air in the proper proportion so that the mixture will burn efficiently in an engine It is the func tion of the engine to convert this mixture into power There are three major factors in an engine which control the change of fuel and air into power 1 Compression 2 Ignition 3 Car buretion Carburetion has been listed last because it is absolutely necessary for the engine to have good compression and good ignition before it can have good carburetion When the average person thinks of carbure tion they immediately think of the carbureter as a unit Carburetion is the combined function o2. 1 Press screwdriver against float axle 22 at slotted side of float hinge bracket and force through hinge bracket 2 Remove float axle 22 completely with fingers from opposite side and remove float 21 Remove fuel valve needle 20 Remove the assembly gasket 23 from the ma chined surface of the throttle body 2 Remove the venturi 24 e f g h i Remove the fuel valve seat 20 and fibre washer 19 from machined surface of throttle body 2 using Zenith Tool No C161 82 Remove the idle jet 18 from passage in machined surface of throttle body 2 near fuel valve seat 20 using a small screwdriver Remove the idle adjusting needle 17 and friction spring 16 from the side of throttle body 2 Remove the throttle plate 1 screws 7 lock washers 8 shaft and stop lever assembly 14 1 Unscrew throttle stop screw 9 until threaded end is flush with lever 18 2 Make match marks with file on throttle body 2 and all levers to act as a guide to reassem ble these parts in the same position as removed 3 Loosen throttle clamp lever screw 11 and remove lever 10 from shaft 14 NOTE Some 161 J Series Carburetors have the throttle lever and the throttle stop lever riveted to gether Omit Step No 3 if this type lever is used 4 File off the riveted or peened end of the throttle plate screws 7 NOTE When such screws are riveted or peened the threaded e
3. is gradually increased and as the idle system begins to diminish the velocity through the venturi 17 is high enough to create a pres sure at the tip of the nozzle 14 slightly less than the pressure in the fuel bow chamber 9 and the accelerating well 16 Fuel therefore feeds from the fuel bowl 1 through the open ing between the power load adjusting needle 18 and the power adjusting needle seat 19 through the power jet 20 and out the nozzle 14 to be discharged into the air stream at the 5 8 nozzle air bleeds 15 to mix with the fuel passing through the nozzle 14 The amount of air that can enter into the nozzle 14 is limited by the size of the nozzle air vent 21 The result of air bleed ing into the nozzle 14 is to help atomize or break up the fuel into finer par ticles to regulate the quan tity and the rate of dis charge of the fuel fed from the accelerating well 16 during acceleration and to provide the correct mixture proportions for full throttle operation ANUAAALAAARAAY As the throttle valve is opened toward the wide open position the velocity through the ven turi 17 continues to increase lowering the air pressure at the nozzle 14 and resulting in additional fuel being supplied to the engine as the speed is increased When the throttle valve 6 is opened sud denly from slow or just off slow idle position the fuel stored in the accelerating well 16 is forced ou
4. and dirt Do not use wire or small drills to clean out small holes as a slight change in size of these holes will affect the carbureter operation To assure a successful overhaul always replace all worn or damaged parts and any parts that are questionable Always use all new gaskets S 14 R1 258 2 54 Rl 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM 19 Install Economizer Jet 20 Install Idle Jet 21 Install Idle Adjusting Needle and Spring Set approximately one turn from seat for preliminary setting 22 Install Float Valve Seat and Gasket Use new Float Valve and Seat Assembly 23 Assemble Bowl Cover Gasket and Venturi in Casting Install float valve 24 Install Float and Lever Assembly and Float Lever Pin Set floats 14 from gasket face to nearest edge of float keeping edge of float parallel with gasket Ad just by using bending tool M 8 25 Install Choke Shaft Packing Retainer and H anvet Packing fe we SCHEBLEA Install retainer as shown in illustrations below Note On some carbureter models the packing is re tained by choke bracket in place of packing retainer 25A On carbureters counter bored to deep in stall retainer with cup facing towards casting Tap hghtly until flush with casting face 25B On carbureters counter bored 35 to 14 deep in stall
5. car buretor employs choke shaft packing wash ers 39 and packing washer retainers 38 in the choke shaft holes around the choke shaft The disassembly of these packing washers and retainers should be performed in the same manner as the disassembly of the throttle shaft packing washers and re tainers which is described in detail in the disassembly of the throttle body NOTE Do not disassemble the choke assembly bracket 28 lever 35 shaft 40 and plate 43 unless there is damage to any one of the above mentioned parts or damage to any of the other component parts of the choke assembly CLEANING AND INSPECTION OF PARTS A CLEANING PARTS a b Clean all metal parts thoroughly with cleaning solution and rinse in solvent Blow out all passages in the air intake and fuel bow casting 49 and throttle body 2 NOTE Be sure all carbon deposits have been removed from throttle bore and idle port It is advisable to re verse flow of compressed air in all passages to insure that all dirt has been removed Never use a wire or drill to clean out jets B INSPECTION OF PARTS a b c d e f g h i j a Float Assembly Replace float assembly 21 if loaded with gasoline damaged or if float axle bear ing is worn excessively Inspect top side of float lever for wear where it contacts fuel valve needle NOTE Such wear can affect the float level Float Axle Replace if a
6. float valve and seat results in a high fuel level in the fuel bow and flooding trouble Both faults can be easily observed by the service man and corrected by replacing worn parts with new ones The proper function ing of the carbureter is obtained by a series of holes drilled to exact size and location which do not wear or change location in service It must be realize that if the carbureter worked correctly at first when passed by the inspectors at the tractor factory it will always function the same provided these passages are all free from dirt On a carbureter complaint from the field the only thing a service man can do to the carbu reter is to disassemble it BE SURE that the passages are open and free from dirt that there is no wear on the throttle shaft and bushings that float valve and seat are O K that the float height is correct and that a good air tight seal exists around the bowl gasket If such carbureter service does not correct the complaints a com plete check of the engine must again be made To check the float setting the casting must be held in an inverted position so that the float lever is in contact with the float valve and the float valve seated Factory Carbureter Model Setti etting Where to Measure Shee tee ay al eee ee Lh pene Jom From the gasket to the nearest surface of the float NOTE Changing the float setting from our standard in an effort to improve the operation of the carbu
7. oil Any adjustments that are necessary on the carbureter should never be attempted until the engine has obtained its normal operating tem perature and the choke valve 25 has been placed in the wide open position Rl 258 2 54 Rl 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM Model TSX Carbureter IDLE ADJUSTING NEEDLE FUEL IDLE ADJUSTING NEEDLE AIR 4 4 i hy NOZZLE k N p a i POWER JET h Na A UN POWER ADJUSTING NEEDLE Fig S 18 BOWL DRAIN Idle and Power Fuel Feed Systems The Marvel Schebler Model TSX Carbureter is manufactured in three S A E nominal sizes inch 1 inch and 114 inch In addition to these vari ations in size there are also variations necessitated by the specific require ment of the engines on which the car bureters are used Many engines for instance require special throttle and choke operating levers and for pur pose of calibration they may have dif ferent size jets nozzles venturi ete For this reason when ordering parts refer to the individual carbureter serv ice parts list for the engine on which the carbureter is installed The Model TSX Carbureter consists of only two major castings 1 The throttle body casting which forms the cover for the fuel bowl 2 The fuel bowl casting which con tains the air inlet ECONOMIZER ORIFICE Cast iron material is used for rug gedness It will be noticed Fig S 18 that all pas
8. supplied through the main jet to a well directly below the main discharge jet The pick up passage is connected to this well by a restricted drilling at the bottom of this passage The fuel travels through this channel to the idle jet calibration The air for the idle mixture originates back of or from behind the main venturi The position of the idle adjusting needle in this passage controls the suction on the idle jet and thereby the idle mixture Turning the needle in closer to its seat results in a greater suction with a smaller amount of air and there fore a richer mixture Turning the needle out away from its seat increases the amount of air y lt car Ty om THROTTLE PLATE 4 IDOLE POSITION PRIMING PLUG _ i IOLE ADJUSTING By NEEOLE ad fi y IDLE AIR li FROM SEWING ETUR Pd iY IDLE JETA IDLE FUEL 7 PICKUP PAS tome i E Yi p Men Willa Ws ts I x _ IDLE SYSTEM Fig S 24 and reduces the suction and a leaner mixture is delivered The fuel is atomized and mixed with the air in the passage leading to the discharge port or priming plug and enters the air stream at this point HIGH SPEED SYSTEM The high speed system controls the fuel mix ture at part throttle speeds and at wide open throttle This system consists of a venturi con trolling the maximum volume of air admitted into the engine the main jet which regulates the flow of fuel from the float chambe
9. the carbure tor The following list of Zenith special tools and general hand tools will best perform the service job b Zenith Special Tools C161 1 Main Jet Wrench C161 10 Plug Wrench C161 25 Main Discharge Wrench C161 71 1 Line Reamer C161 72 1 Bushing Driver C161 73 1 Counter Bore Reamer C161 82 Fuel Valve Seat Wrench C161 83 Main Jet Wrench c General Hand Tools 7 16 Open End Wrench 1 2 Open End Wrench 1 4 Blade Screw Driver Long Nosed Pliers 6 Depth Gage 1 4 Round File Light Hammer Long Rod or Punch S 21 d b c GROUP II ENGINE SECTION S FUEL SYSTEM The basic repair parts kit for the 61 or 161 carbure tor except model 61A8SRD is No K501 A proper repair job cannot be performed however by using the basic kit as such The basic kit must be tail ored to fit the particular outline of the carburetor being serviced by the addition of the parts listed in large print on the label of the basic kit container Fig S 28 D SEPARATE CARBURETOR BODIES a Remove the hex plug or filter screen 15 from side of throttle body 2 using a 7 16 wrench Remove the four assembly screws 52 and lock washers 51 which attach the throttle body 2 to the fuel bowl 49 using a screwdriver Separate the throttle body 2 from the fuel bowl assembly 49 E DISASSEMBLE THROTTLE BODY a b c d 022 Remove float axle as follows
10. E SECTION S FUEL SYSTEM The Idle System D THROTTLE Yy Yy VALVE 6 A Ds Ny BY SECONDARY pe IDLE ORIFICE 8 GA Ka 3 VASO gw PRIMARY IDLE ORIFICE 7 the throttle valve 6 since this valve must be slightly open to permit the engine to idle The resultant mix ture is correct for operat ing engine at idle speed provided the idle adjust IDLE ADJUSTING NEEDLE 13 Pee ere a a a C L LLL LLG Whur A l ing needle 13 is prop IDLE NE TE A y Q FUEL BOWL A erly adjusted CHAMBER 9 N S NEEDLE SEAT 12 w N 1 IDLE JET 11 Wis 7 7 ee eas a IDLE FUEL PASSAGE 10 ky Fig S 14 The idle system controls the flow of fuel at idle speed and at slow speeds until the throttle is opened wide enough to allow the power fuel feed system to function When the throttle valve 6 is in the idle posi tion the edge of the valve is between the primary idle orifice 7 and the secondary idle orifice 8 With the valve in this position the air pres sure manifold vacuum at the primary idle orifice 7 is lower than the air pressure in the fuel bow chamber 9 and fuel is forced from the fuel bowl 1 into the idle fuel passage 10 As the fuel travels through the idle fuel passage 10 it passes through the metering orifice of the idle jet 11 tothe point where it is combined with air entering through the idle adjustin
11. GROUP II ENGINE SECTION S FUEL SYSTEM NOTE A lathe may be substituted for the drill press in performing the counter boring and line reaming operations Install the two new throttle shaft packings 4 and retainers 5 in throttle body 2 as follows Use bushing driver tool Zenith C161 72 1 1 Assemble packing 4 and retainer 5 and place completed assembly on bushing driver tool with packing facing small end of tool 2 Insert small end of tool into throttle shaft hole start retainer 5 into counter bore in body 2 and lightly drive retainer 5 into body 2 until it is flush with machined surface NOTE The packing retainer 5 must be flush with machined surface or slightly below to avoid striking throttle lever 18 Install the throttle shaft and stop lever assembly 14 throttle plate 1 screws 7 and lockwashers 8 as follows 1 Insert the throttie shaft and stop lever assem bly 14 in throttle body 2 2 Rotate throttle shaft 6 to wide open position insert throttle plate 1 and rotate to closed position holding the plate in position with fin gers 3 Start throttle plate screws 7 and lockwashers 8 and tighten with small screwdriver being sure that the throttle plate 1 is properly cen tered in the throttle body bore NOTE The screw holes in the throttle plate are off center Start the side of the throttle plate with the shortest distance between the screw holes and beveled edge i
12. adjusting and regulating the power fuel mixture ratio as well as the idle Now in service con sider that the compression ignition and timing have been checked and found to be 100 in this engine If the air intake temperature and the water temperature is held constant then the only variable we have that affects maximum horsepower is the fuel mixture ratio If compression ignition and timing which are variable are first properly checked by a service man and set to factory specifications very little difficulty will be experienced in ad justing the carbureter to give the maximum horsepower and economy A great deal has been said regarding the im portance of engine tune up and the reasons for service men being exact in their service work on engines The reasons why a carbureter may not S 17 GROUP II ENGINE SECTION S FUEL SYSTEM function properly when everything else has been checked and set to factory standards will now be covered With the present type carbureter construction used on Marvel Schebler tractor and industrial carbureters not very much can go wrong with the possible exception that it may foul with dirt There are only two places that are subject to wear the throttle shaft and bushings and the float valve and seat The wear on the throttle shaft and bushings and resultant air leak there from results in a lean idle and to compensate for the air leak more fuel must be turned on for idle Wear on the
13. alve for any signs of wear If it is not absolutely true or is grooved and hasn t a perfect taper a new float valve and also a new float valve seat must be used These float valves and seats are supplied in match ed sets and are tested at the factory for leaks Always use a new float valve seat gasket to make sure of a perfect seal 2 Examine float for any signs of failure To test metal float submerge float in pan of hot water and if air bubbles are observed replace with new float Examine cork float for bare places or cracks in coating If either are found or if float shows evidence of having been soggy replace with new one Do not attempt to recover float with shellac or varnish set float height to the proper specification for the particular model carbureter being serviced Make certain that the entire assembly works free and that there is no binding Wash fuel strainer assembly in gasoline and clean screen with air under pressure If the screen or the threads on the strainer are not in good condition install a new assembly When re installing fuel strainer assembly always use a new strainer gasket if a gasket is used to obtain a seal It has been proven with few exceptions that with a float system in good order carbureter flooding only occurs when dirt or foreign matter becomes lodged between the float valve 3 and float valve seat 4 R1 258 2 54 R1 258 2 54 GROUP Ii ENGIN
14. as a fuel ad justing idle needle It is important to remember in setting the idle mixture the air adjusting idle needle must be turned in or clockwise to enrich the idle mixture and the fuel adjusting idle needle must be turned out or counter clockwise to enrich the idle mixture A dual float mechanism Fig S 20 is used in a fuel bowl that almost com pletely surrounds the nozzle This de sign and construction is such that the tractor or engine can be operated at any angle up to 45 degrees without seriously affecting the fuel and air ratio and without flooding because the mean level at the nozzle tip is practi cally constant at any angle of opera tion Some carbureters are equipped with a spring loaded governor control lever to permit manual closing of the throttle to an idle position for engines equipped with certain type governors An example of this type lever is shown in Figure 4 however there are other variations of this type dependent upon the particular application While there are many variations produced by combining the different types and sizes into a specific application all Model TSX carbureters incorporate the same engineering principles and are alike from a functional standpoint Fig S 21 Spring Loaded Governor Lever RI 258 2 54 Rl 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM Service Instructions for Model TSX Carbureters MARVEL Type A Fixed Jet SCHEBLER Ty
15. dle assembly 56 and fibre washer 55 from bottom of fuel bowl body 49 using a 12 wrench NOTE Some models will have a plug hex in place of the adjustment Remove the drain plug hex 50 from outside bottom of fuel bowl 49 using Zenith Tool No C161 10 Remove main jet 54 and fibre washer 53 from threaded passage in bottom side of fuel bowl 49 with Zenith Tool No C161 1 Remove main discharge jet 25 and fibre washer 26 from center of large opening in machined sur face of fuel bowl 49 with Zenith Tool No C161 25 Remove well vent jet 27 from center of large opening in machined surface of the fuel bowl 49 with a small screwdriver Disassemble choke as follows 1 Remove the bracket spring 37 from the choke lever 35 and choke bracket 28 2 Make match marks with a file on air shutter bracket 28 air intake body 49 and lever 35 to act as a guide to reassemble these parts in the same position as removed 3 Remove the choke shaft nut 33 and lock washer 32 using Zenith Tool No C161 25 4 Remove the choke lever 35 5 Remove the choke bracket screw 36 using a 1 open end wrench and remove choke bracket 28 6 Remove the shaft hole plug 44 and fibre washer 45 using a open end wrench 7 Remove the choke plate screws 42 and lock washers 41 and remove the choke shaft 40 and choke plate 48 NOTE Some models of the Zenith 161 J Series
16. e distributor cap which causes corrosion and weak spark The spark timing of the engine is most im portant and should also be checked very care fully and set exactly on the mark as called for in factory standard specifications In fact all of the above items must be checked very care fully to factory standards and not just given a casual inspection with the common expression Everything looks O K You can KNOW defi nitely that the tractor is up to the standards set by the manufacturer POWER AND ECONOMY LOW Complaints are received from the field that the engine will not pull or develop its maximum horsepower or that it develops good power but uses far too much fuel Too often a service man will at once change the carbureter to correct these complaints but by so doing he may not be successful in overcoming the difficulty It must be clearly understood by all service men that when a new engine is designed and developed the management first decides what horsepower they want this engine to produce at a definite rated speed The engineering depart ment develops the new engine to pull the re quired horsepower In the design there are cer tain fixed dimensions that never change For instance the bore and stroke the displacement compression ratio diameter of valves lift of valves diameter of intake passage The carbu reter engineer works out the diameter of throttle bore venturi size and provides for means of
17. e has been run sufficiently to bring up to operating temperature throughout see that choke is returned to wide open position LOW SPEED OR IDLE ADJUSTMENT Set throttle or governor control lever in slow idle position and adjust throttle stop screw for the correct engine idle speed On a new stiff engine this speed must be slightly higher than required for a thoroughly run in engine Turn idle adjusting needle until engine begins to falter or roll from richness then turn needle in the opposite direction until the engine runs smoothly NOTE It is better that this adjustment be slightly too rich than too lean IDLE ADJUSTING NEEDLE AIR ADJUSTING To richen the idle mixture turn the idle adjusting needle to the right or clockwise IDLE ADJUSTING NEEDLE FUEL ADJUSTING To richen the idle mixture turn the idle adjusting needle to the left or counter clockwise POWER OR LOAD ADJUSTMENT TYPE B TYPE C With the engine running at governed speed under load turn power adjusting needle to the right or clockwise a little at a time until the power drops appreciably Then turn the needle to the left or counter clockwise until the engine picks up power and runs smoothly This will give an economical part throttle mixture and due to the economizer action the proper power mixture for full throttle operation Due to variations in temperature or fuels it may be necessary to richen up this mixture by backing out the power adjus
18. el bowl This system allows economical fuel mixture ratios for part throttle operation while still per mitting the richer mixture ratios that are needed for full load operation The economizer system performs its function by establishing a back suction on the fuel in the fuel bowl during most of the part throttle range of operation This back suction is created by manifold vacuum through the channels con necting the throttle bore with the fuel bowl This retards the flow of fuel through the metering systems and thus permits the carburetor to oper ate on leaner part throttle mixture ratios The rotation of the throttle shaft controls the economizer system During part throttle oper ation from about one quarter to three quarters throttle the passages are open and the pressure in the fuel bowl is lowered This retards the flow through the main jet and a leaner mixture is supplied n full throttle opening the passages are closed and the main jet flows to full capacity to supply the richer mixture required CHOKE SYSTEM The choke system consists of a valve mounted on a shaft located in the air entrance and oper ated externally by a lever mounted on the shaft The choke valve is used to restrict the air enter ing the carburetor This increases the suction on g ay CHOKE j CLOSED POSITION ka f 4 f E m F POPPET VALVE Y Wy K i PARTIALLY OPEN Wj CHOKE SYSTEM Fig S 27 the jets when starting
19. el bowl throughout the oper ating range of the engine When the fuel bowl 1 is empty the float and lever 2 and float valve 3 drop and fuel under pressure from the fuel pump or gravity feed is forced through the float valve seat 4 around the float valve 8 and into the fuel bowl 1 As the fuel in the bowl approaches the correct operating level it raises the float and lever 2 with enough force to raise the float valve and cut off the flow of fuel into the bowl As fuel feeds through the carbureter jets into the engine the fuel level 5 drops allowing additional fuel to enter the fuel bowl Under actual operating conditions the fuel level 5 and float and lever 2 automatically position themselves so that the inward flow of gasoline to the carbureter is equal to the out ward flow of gasoline to the engine As can readily be seen the float system under the most favorable of operating conditions is subjected to a certain amount of wear Under severe conditions or conditions that result In ex cessive vibrations being transmitted to the carbu reter float valve and float valve seat wear is accelerated S 6 Ears LIZZIE FLOAT re eee N aes pepee FUEL LEV EL i 3 ie oe oe m a os ra PE DHO a 4 3 A SSS FUEL BOWL 1 It should be an estab lished policy that when ever the carbureter is dis assembled for whatever aa Cause the service man HH make following checks A AAA D 1 Examine float v
20. er orifice machined in the carbureter throttle body regulates the fuel sup plied to the engine In addition there are engine and carbureter combinations that do not require the back suction economizer system In these carbureters the economizer orifice has not been machined in the throttle body casting To provide additional economy in addition to the back suction economizer system some carbu reters are provided with two adjusting needles the low speed or idle adjusting needle and the power or load adjusting needle However the power adjusting needle is not always required and for applications of this nature the fixed jet type carbureter is used in which the power jet controls the amount of fuel that is supplied to the engine There are two variations in carbureters hav ing the power adjusting needle commonly called the adjustable jet type carbureter In Fig S 18 is shown these two arrangements The adjust ment of either type is accomplished in the same manner A large percentage of the Mode TSX Carbu reters are provided with an idle adjusting needle which alters the fuel and air proportions of the mixture which enters the carbureter bore from the idle passage This is known as an S 12 FLOAT VALVE SEAT air adjusting idle needle The upper inset in Fig S 18 shows an idle adjust ing needle which alters the amount of fuel and air mixture which enters the carbureter bore from the idle passage This is commonly known
21. f the carbureter manifold valves piston and rings combustion chamber and cam shaft It can be readily seen that carburetion is a far deeper subject than consideration of the car bureter alone and expecting the carbureter to cure faulty ignition compression valves etc will only result in wasted time and effort on the part of the service man and added expense to the customer It must be remembered that the function of the carbureter does not extend beyond deliver ing the proper mixture of fuel and air to the manifold and the other factors which effect power and economy cannot be changed or cor rected by the carbureter Inability to understand all the factors that effect engine operation is the reason many service mechanics change from fac tory standards and attempt to improve on the engine set up by their own methods or stand ards All that any service mechanic should ever try to do is to make the particular engine he is working on as good as the manufacturer in tended it to be but he can make it a lot worse Far too many engines are running below their standard of performance in service today For the carbureter to accomplish its function it must be able to vary the mixture strength de pendent upon the engine demands It must supply a mixture strength that will allow the en gine to give maximum horsepower whenever the throttle is fully opened while at part throttle conditions it must lean out the
22. g 1 023 or 1 Yg X7 g 1 023 or 1 lag XXT Yg 1 023 or 1 114 8 1 1 181 or 1 r FUEL SUPPLY SYSTEM The fuel supply system is made up of the threaded fuel inlet the fuel valve seat fuel valve float and fuel bowl The fuel supply line is connected to the thread ed inlet The fuel travels through the fuel valve seat and passes around the fuel valve and into the fuel bowl The level of the fuel in the fuel chamber is regulated by the float through its control of the fuel valve The fuel valve does not open and close alternately but assumes an open ing regulated by the float sufficient to maintain a proper level in the fuel chamber equal to the nn y A P iy FUEL INLET Y FUEL VALVE BOWL VENT SEAT PASSAGE Fi E RRGE FUEL e NEEOLE FLOAT ip ky FUEL BOWL FUEL SUPPLY SYSTEM Fig S 23 demand of the enyine according to its speed and load The inside bow vent as illustrated by the pas sage originating in the air intake and continuing through to the fuel bowl is a method of venting the fuel bow to maintain proper air fuel mixtures even though the air cleaner may become re stricted This balancing is frequently referred to as an inside bowl vent S 19 GROUP II ENGINE SECTION S FUEL SYSTEM IDLE SYSTEM The idle system consists of the idle discharge port idle air passage idle adjusting needle idle jet and fuel passage The fuel for idle is
23. g needle seat 12 The mixing of air with gasoline helps to atomize the fuel and this process is repeated at the secondary idle orifice 8 as the fuel travels through the idle fuel passage 10 As this rich mixture of fuel and air emerges from the primary idle orifice 7 it is reduced to cor rect proportions by the air which passes around NSS As the throttle valve 6 pore DANE sea ETna PeT EG tithe is slowly opened from the slow idle position it gradu ally subjects the second ary idle orifice 8 to in take manifold vacuum and the secondary idle orifice 8 no longer bleeds air to the idle fuel passage 10 but feeds an addi tional quantity of fuel into the engine This is proper since the throttle valve is now open wider and will admit a greater amount of air to blend with this additional fuel to maintain the correct proportions of fuel and air for the engine As the throttle valve 6 is opened still wider the idle fuel delivery begins to fade out how ever the throttle valve at this point is far enough open for the power fuel feed system to begin functioning The idle system as described above is the most positive and satisfactory of idle systems as it is working under very high suction and the mixture fiows through the small passages and orifices at very high velocities It is necessary to bear in mind however that there are times when these small holes may become plugged with particles of dirt o
24. ion of float assembly for correct measurement to obtain proper float level using a depth gage Obtain float setting measure ment from outline specification chart NOTE Do not bend twist or apply pressure on the float bodies 1 With bowl cover assembly 2 in an inverted position viewed from free end of float 21 the float bodies must be centered and at right angles to the machined surface The float set ting is measured from the machined surface no gasket of cover to top side of float bodies at highest point 2 Bending Float Lever To increase or decrease distance between float body and machined sur face use long nosed pliers and bend lever closa to float body NOTE Replace with new float if position is off more than 1 16 k Insert venturi 24 in throttle body bore large opening first C ASSEMBLE CARBURETOR BODIES a Assemble the two completed bodies 2 and 49 and four screws 52 and lockwashers 51 and tighten screws evenly and firmly b Install the hex plug or filter screen 15 in threaded passage in throttle body 2 C161 10 wrench c Hold the throttle lever 13 in a closed position and turn the throttle stop screw 9 in until it just contacts the stop on body 2 then turn screw 9 in 1 additional turns AVIATION CORPORATION S 25
25. l be enough light ends to combine with the air to form a com bustible mixture for starting the engine The function of the choke valve 25 is to restrict the amount of air that can enter the car bureter and to increase the suction on the nozzle 14 so that additional fuel will be drawn into the manifold As soon as the engine fires and runs the rich mixture must be rapidly reduced to prevent stalling This change in mixture is ac complished by the operator positioning the choke valve to provide the proper mixture However afew degrees movement of the choke valve 25 will make a big change in the mixture strength and to help reduce the sensitivity of the choke S 10 valve 25 position use is made of a spring loaded relief valve 26 in many applications This valve opens automatically with engine speed and load and eliminates a great deal of manipulation of the choke on the part of the operator When the engine has obtained normal oper ating temperature the choke valve 25 must be fully opened to assure maximum power and economy In addition extended use of the choke results in more gasoline being supplied to the engine than can be burned A large percentage of the unburned gasoline is lost through the ex haust system The remainder of the raw gasoline is forced between the pistons and cylinder walls washing away the protective oil film and increas ing engine wear and enters the crankcase where it dilutes the engine
26. mixture so that maximum economy can be obtained In addition it must have flexibility throughout the entire range of operating speeds from idle and part throttle to full power wide open throttle posi tion The carbureter must also have an acceler ating well with enough fuel capacity to start handling sudden maximum loads In other words the carbureter not only varies the volume of fuel and air that enters the engine but also varies the amount of fuel that goes in with a given amount of air in order to produce the proper mixture proportion for any condition under which the engine is operating at any time In order to understand the function and opera tion of the Marvel Schebler Tractor and Indus trial Carbureters it is well to consider the systems that make up each carbureter These systems are The Float System The Idle System The Power Fuel Feed System The Back Suction Economizer System and The Choke System A thorough knowledge of each system will help the service mechanic to quickly locate and correct legitimate carbureter complaints as well as to inspect repair and put back to standard any carbureter that requires an overhaul 3 5 GROUP II ENGINE SECTION S FUEL SYSTEM Float System K A Au PLAT VALVE L WSS LEVER 2 ULLLLLLILLILLLI LESS z ee ee ee P beat Ff Ppbm ee a8 op Lids Fig S 13 The float system controls the level and supply of gasoline in the fu
27. nd of the two screws must be filed flat before removal to avoid breakage or stripping of threads in the shaft In some cases it may be necessary to use a small 4 4 round file and cut slightly below the surface of the shaft because of a slight counter bore around the screw hole Be sure to avoid striking and cutting the side of the throttle body bore or the throttle plate when filing the screws 5 Remove the screws 7 and pull out the throttle plate 1 6 Remove the throttle shaft and stop lever assem bly 14 from the throttle body 2 Remove the throttle shaft packing 4 and packing retainer 5 from the throttle body shaft holes as follows 1 Screw a 5 16 fine thread taper tap into pack ing retainer 5 until it is firmly seated 2 Insert long punch or rod through opposite shaft hole and drive punch against the end of the tap until retainer 5 is free of the body Repeat operation for other packing and retainer NOTE Do not disassemble the throttle plate 1 throttle shaft and stop lever assembly 14 throttle packing 4 and packing retainer 5 from the throttle body 2 unless the throttle shaft is bent or otherwise damaged or unless there is damage to any of the other component parts of the throttle as sembly Ri 258 2 54 RI 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM F DISSASEMBLE FUEL BOWL BODY a b c d e Remove the main jet adjusting nee
28. nto the shaft first The throttle plates are made with two op posite edges beveled to fit the throttle body bore when the plate is closed The throttle plate will not close tightly if installed upside down To properly center the plate in the throttle body bore the screws should be started in the shaft and then with the plate closed it should be tapped on the mounting flange side Pressure on the plate must be maintained with the finger until the screws are tightened When properly installed the side of the throttle plate farthest away from the mounting flange will be aligned with the idle port when the plate is closed Install throttle clamp lever in same position as re moved Refer to match marks placed on lever and throttle body during disassembly step Install idle adjusting needle 17 and friction spring 16 in threaded passage on side of throttle body 2 Seat lightly with screwdriver and back out 1 full turns Install idle jet 18 in counter bored passage in machined surface Printed with permission of ZENITH CARBURETOR DIVISION g Install fuel valve seat 20 and fibre washer 19 using Zenith Tool No C161 82 h Place new throttle body to fuel bowl gasket 23 on machined surface of fuel bowl cover 2 i Install fuel valve needle 20 in seat 20 followed by float 21 and float axle 22 Fig S 29 The A dimension should be 1 5 32 plus or minus 3 64 j Float Level Check posit
29. ny wear can be visually detected on the bearing surface Fuel Valve Seat and Needle Assembly Always replace fuel valve seat and needle 20 because both parts wear and may cause improper float level Idling Adjusting Needle and Spring Inspect point of needle 17 This must be smooth and free of ridges Throttle Plate Inspect plate 1 for burrs or damaged edges Never clean a throttle plate with a buffing wheel or sharp instrument Choke Plate 48 damaged edges Inspect for bends burrs or Choke Shaft Check bearing surfaces for wear see that shaft 40 is straight Gaskets Replace all gaskets and fibre washers every time the carburetor is disassembled Throttle Shaft Replace if throttle shaft 6 shows evidence of wear on the bearing surfaces Check Specifications Use the outline specification chart and verify the correctness of the following parts Numbers shown on chart will be found on parts The following calibrated parts should be checked Venturi Main Jet Discharge Jet Well Vent Jet Idling Jet and Fuel Valve Seat REASSEMBLY A FUEL BOWL BODY Choke Assembly 1 Install the two choke shaft packings 39 and retainers 38 in fuel bowl body 49 as follows Use bushing driver tool Zenith C161 72 1 2 Assemble packing 89 and retainer 38 and place completed assembly on bushing driver tool with packing facing small end of tool 23 R1 258 2 54 b c d e f
30. ove Main Nozzle and Gasket Type A Type B De Remove Power Jet Type A Type B 12 Remove Power Adjusting Needle Assembly Type C Carbureters not having adjustable needle remove power jet 13 Remove Main Nozzle and Gasket Type C FUEL SYSTEM jae Remove Retainer Plug and Gasoline Drain Strainer Strainer can only be re placed on carbureters hav ing a curled hair or felt type strainer Only re place when impossible to clean with gasoline and compressed air Porous metal type strainer can not be replaced Clean only 15 Remove Choke Valve Screws Valve Choke Shaft amp Lever Assembly Choke Return Spring and Choke Bracket 16 Remove Choke Shaft Packing Retainer and Packing Foree out retainer with small screwdriver or punch ASSEMBLE 17 Install Throttle Shaft Packing and Retainer Assemble new retainer and packing on throtfle shaft Insert shaft in carbureter and tap lightly until retainer is flush with casting face 18 Install Throttle Valve and Screws Install valve with angle identification mark facing flange face of carbureter Tap valve lightly to cen ter in throttle bore Tight en screws securely MARVEL SCHEBLEA Before assembling carbureter clean castings channels and parts with carbureter cleaning fluid and air under pressure Make certain all small holes and channels are open and free from carbon
31. pe B Adjustable Jet Type C Adjustable Jet The following procedure for service of all Model TSX Carbureters is for a complete overhaul After removing carbureter from engine wash thoroughly with cleaning fluid such as gasoline to permit examination of external parts for damage For type carbureter being serviced see illustrations above Instructions apply to all types unless specified otherwise 1 Remove Power Adjusting Needle Assembly Type B 2 Remove Bowl Cover Screws and Lock Washers Separate Castings 3 Remove Float Valve Bowl Gasket and Venturi If Valve is grooved or damaged replace Valve and Float Valve Seat f ER Remove Float Valve Seat and Gasket B Remove Economizer Jet NOTE Not required in all carbureters Check service parts list or repair kit of earbureter being serviced 6 Remove Idle Jet NOTE Not required in all carbureters Check service parts list or repair kit of carbureter being serviced 7 Removing Idle Adjusting Needle and Spring Replace with new Needle if grooved or damaged g8g Remove Throttle Valve Screws Valve and Throttle Shaft and Lever Assembly Replace with new shaft and lever assembly if ex cessive looseness between shaft and throttle body GROUP II ENGINE SECTION S g Remove Throttle Shaft Packing Retainer and Packing Foree out Retainer with small serewdriver or punch 10 Rem
32. r foreign matter and will require clean ing At such times the passages jets and small drilled holes should only be cleaned with a cleaning fluid such as gasoline and air under pressure Never use drills or wires as a change in size of these small openings will change the entire calibration of the carbureter S 7 GROUP II ENGINE SECTION S FUEL SYSTEM Power Fuel Feed System AL THROTTLE VALVE 6 NOZZLE AIR VENT 21 LLM ALA MeL f z a a oy Peal VENTURI 17 W A T ee WEG Ss FUEL BOWL CHAMEBER Ww venturi 17 At the same time the fuel that is stored in the accelerating well 16 is also forced through the nozzle air bleeds 15 into the nozzle 14 But because the size of the power jet 20 and the position of the power ad justing needle 18 restrict the amount of fuel which can enter the nozzle 14 the fuel in the accelerat ing well 16 will soon be exhausted and air will then enter through the lt ACCELERATING WELL 1I6 Fr POWER JET 20 A POWER ADJUSTING NEEDLE 18 Fig S 15 With the throttle valve 6 in slow or just off slow idle position fuel rises up through the nozzle 14 and out the nozzle air bleeds 15 to fill the accelerating well 16 to approxi mately the height of the fuel level in the fuel bowl 1 As the engine speed is increased from the slow idle position the air flow through the venturi 17
33. r to the main discharge jet the well vent which maintains uniform mixture ratio under changing suction and engine speeds and a main discharge jet which delivers the fuel into the air stream The main jet controls the fuel delivery during the part throttle range from about one quarter S 20 bie o e VENTURI MAIN DISCHARGE JET a HIGH SPEED SYSTEM Fig S 25 to full throttle opening To maintain a proper mixture ratio a small amount of air is admitted through the well vent into the discharge jet through the air bleed holes in the discharge jet at a point below the level of fuel in the metering well The passage of fuel through the high speed system is not a complicated process The fuel flows from the fuel chamber through the main jet and into the main discharge jet where it is mixed with air admitted by the well vent and the air fuel mixture is then discharged into the air stream of the carburetor VACUUM PASSAGE Y z Ly ECONOMIZER e kea RESTRICTION ECONOMIZER CALIBRATION LLLA M BACK SUCTION ECONOMIZER SYSTEM Fig S 26 ECONOMIZER SYSTEM The economizer system consists of a milled slot in the throttle shaft which acts as a valve to open or close the system a vacuum passage from the throttle bore to the slot in the throttle R1 258 2 54 R1 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM shaft and a vacuum passage from the slot in the throttle shaft to the fu
34. retainer with cup facing away from casting Tap lightly until flush with casting face 26 Install Choke Bracket Choke Return Spring Choke Shaft and Lever Assembly Valve and Screws Center valve in casting before tightening screws 27 Install Power Jet Type A Type B 28 Install Main Nozzle and Gasket Type A Type B Use new gasket GROUP II ENGINE SECTION S FUEL SYSTEM 29 Install Main Nozzle and Gasket Type C Use new gasket 30 Install Power Adjusting Needle Assembly Type C Use new gasket Set approximately one turn from seat for preliminary setting lais Install Gasoline Drain Strainer amp Retainer Plug Stake retainer plug in place with center punch to insure secure locking 32 Assemble Castings Invert throttle body and lower fuel bowl over floats taking precaution that venturi guides bodies into position palace 73Aue 33 Install Bowl Cover Screws and Lock Washers Tighten screws gradually until all are tight RvEL psa 34 Install Power Adjusting Needle Assembly Type A Set approximately one turn from seat for preliminary setting Adjustment Instructions PRELIMINARY ADJUSTMENTS Set throttle stop screw so that throttle valve is open slightly Make certain that fuel supply to carbureter is open Close choke valve Start engine and partially release choke After the engin
35. reter or in an effort to prevent flooding will only result in faulty carbureter operation Printed with permission of Marvel Schebler Products Division Borg Warner Corporation RI 258 2 54 Rl 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM ZENITH 61 ak i ae Fig S 22 The Zenith 61 and 161 Series carburetors are of updraft single venturi design They are made in 59 and 7 S A E barrel sizes with 52 7 1 and 114 S A E flange sizes available They are made with selective fuel inlet with or with out a back suction economizer and a main jet adjustment They are balanced and sealed and the semi concentric fuel bow allows operation to quite extreme angles without flooding or starving This design makes them particularly adaptable to smaller farm tractors and a great variety of agricultural machines and industrial units MODEL DESIGNATION Ty pe Updraft Material Barrel and bowl castings cast iron Styles A Throttle and choke shafts parallel D Equipped with degasser assembly E Elbow air intake J Back suction economizer R Built in governor S Straight through air intake X Flange next size larger than stand ard XX Flange second size larger than standard AND 161 SERIES CARBURETORS Size Nominal Throttie Bore Flange Size Designation Size Diameter S A E Standard 5 y T8Tor 8 3 T Y
36. s or limits the amount of air that can enter the fuel bow chamber 9 The ECONOMIZER ORIFICE 24 RW ZA NAAANANANAANAAANNAANAANY amount of air that is drawn out of the fuel bowl chamber 9 is controlled by the size of the economizer jet 23 the economizer orifice 24 and the position of the throttle valve 6 as its position determines the manifold vacuum or suction on the econo mizer orifice 24 As the throttle valve 6 is opened from the fast idle position the economizer orifice 24 is gradually ex posed to manifold suction and air flows from the fuel bowl chamber 9 through the economizer jet 28 and out the econo mizer orifice 24 This air must be re placed by air entering through the bowl vent 22 but as the size of the bow vent 22 restricts the amount of air that can enter the resultant pressure in the fuel bowl chamber 9 will be lowered reduc ing the difference in air pressure between the nozzle 14 and the fuel bowl chamber 9 The flow of fuel will therefore be re tarded so that the exact economy mixture ratio will be delivered to the engine at this particular throttle opening Opening the throttle valve 6 further exposes the entire economizer orifice 24 to manifold suction resulting in additional air being removed from the fuel bowl chamber 9 again leaning out the mixture ratio to the correct proportions for this new throttle position After the econo mizer orifice 24 is fully expo
37. sages whenever possible are drilled from the top face of the fuel bowl casting to prevent any fuel leaks to the outside of the carbureter because of shrunken gaskets or defec i BOWL VENT Fig S 19 Back Suction Economizer System tive hole plugs and also to prevent vapor lock or percolation of the fuel when the carbureter is operated under ex tremely hot conditions resulting in hard start ing or erratic engine op eration The Model TSX carbu reter is completely seal ed against dust or dirt All air entering the fuel bowl of the carbureter must first pass through the air cleaner The throttle shaft bearings and choke shaft bear ings are sealed to elimi nate dust and dirt enter ing at these points The back suction econ omizer system Fig S 19 is provided with a removable economizer jet The size of this jet has been carefully es tablished by engineer ing tests to provide the exact fuel requirements for maximum economy at part throttle opera tion Always use the economizer jet specified in the individual carbureter service parts list to assure proper engine operation On some carbu Bm ECONOMIZER JET GROUP II ENGINE SECTION S FUEL SYSTEM Model TSX Carbureter FLOAT VALVE CHOKE VALVE GASOLINE DRAIN STRAINER Fig S 20 Float and Choke Systems reter models the proper fuel requirements are established without the use of an economizer jet and the fixed economiz
38. sed to manifold suction the amount of air that is drawn out of the fuel bowl chamber 9 is controlled by the manifold vacuum or suction at any given throttle valve 6 position and as this suction decreases as the throttle approaches wide open position less air is drawn out of the fuel bowl chamber and additional fuel flows to the engine to provide the extra richness required for operation at heavy loads where maximum horsepower is necessary The Back Suction Economizer System as sures the proper metering of fuel to the engine throughout the service life of the carbureter as there are no moving parts to wear out or adjust ments to get out of order It is essential how ever that the system remain free of dirt and foreign matter because any foreign substance in the system will restrict the flow of air thereby creating improper pressures in the fuel bowl chamber and resulting improper fuel delivery to the engine 3 9 a GROUP II ENGINE SECTION S FUEL SYSTEM we ASSAS AAA 7AA iiiiiiiiii ll Fig S 17 The choke system is used during cold starting and the warm up period Under these cold con ditions it is necessary to supply an additional rich mixture of fuel and air as only the light ends or more volatile portions of the fuel will vaporize with the manifold and air tempera tures at these cold conditions Consequently it is necessary that a large quantity of fuel be available so that there wil
39. t through the nozzle air bleeds 15 very rapidly and serves to provide the extra richness required by the engine to meet the sudden load When the throttle valve 6 is closed fuel again fills the accelerating well 16 ready for the next acceleration Rl 258 2 54 Rl 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM Back Suction Economizer System THROTTLE VALVE 6 Fig S 16 The amount of fuel supplied to an engine is controlled by the size of the power jet the po sition of the power adjusting needle and the difference in air pressure between the fuel bowl chamber and the venturi However in many engines the mixture must be leaned out addi tionally during part throttle operation to obtain maximum economy To provide this leaner mixture Marvel Schebler Tractor and Industrial Carbureters make use of the Back Suction Economizer System With this method of meter ing fuel the air pressure in the fuel bowl chamber is regulated and controlled according to load conditions by a combination of bowl vent and economizer passages communicating with the throttle bore of the carbureter Through regulations of the air pressure in the fuel bowl chamber the fuel flow through the carbureter can be controlled to provide the prop er mixture proportions for the engine All the air that enters the fuel bowl chamber 9 must first pass through the air cleaner and the bow vent 22 The size of the bowl vent 22 control
40. the engine The choke valve is of a semi automatic type having a poppet valve incorporated in its design which is controlled by a spring The poppet valve opens automatically when the engine starts and admits air to avoid over choking or flooding of the engine The mixture required for starting is considerably richer than that needed to develop power at normal temperatures As the engine fires and speed and suction are in creased the mixture ratio must be rapidly re duced This change is accomplished through ad justment of the choke valve and the automatic opening of the poppet valve to admit more air when the engine fires SERVICE AND REPAIR PROCEDURE A IDENTIFY CARBURETOR a Check the numbers on metal identification disc riveted to top of float bowl cover against carburetor outline specification chart The inside number next to the rivet is the Zenith outline assembly number and the one next to the outer edge of the disc is the vehicle manufacturer s B DISASSEMBLED VIEW a The disassembled view will identify the various com ponent parts and show their relation to assembly Use the disassembled view with the identifying part numbers to identify and locate parts when perform ing the disassembly and reassembly operations C SELECTION OF TOOLS AND REPAIR PARTS KIT a The use of the proper Zenith tools and the proper repair parts kits is essential if the best service and repair procedure is to be preformed on
41. ting needle a small amount at a time until good acceleration is obtained NOTE Carbureters TSX 107 TSX 330 TSX 339 TSX 355 TSX 385 and TSX 398 use the fuel ad justing type idle needle All other Model TSX Carbureters use the air adjusting type idle needle Rl 258 2 54 RI 258 2 54 GROUP II ENGINE SECTION S FUEL SYSTEM Service Complaints IDLE UNEVEN IN OPERATION The idle construction used in Marvel Schebler Tractor and Industrial Carbureters 1s the most positive and satisfactorv of idle systems because it is working under very high suction and the mixture flows through the small passages at very high velocities It is necessary to bear in mind however that there are times when these small holes may become plugged with particles of dirt or lint but very seldom If idle trouble is experi enced first check the manifold to cylinder head gasket and the carbureter to manifold gasket for air leaks At slow idle an engine requires only approximately 20 to 25 lbs of air per hour and a slight leak will result in a very erratic or rough idling engine Other causes for a rough idling engine are uneven compression caused by sticky or leaking valves leaking valve seats tappets with im proper clearances leakage past pistons and rings cylinder head gasket leaking weak spark or spark plug points not spaced correctly ignition cable covering cracked and thus ground ing spark and cable not assembled properly in th
Download Pdf Manuals
Related Search