MODELS B,BC,BV - MANUAL
Contents
1. BULLETIN 9D 2 MODELS B BC BV PR United W Delco LACES BULLETINS IN D SECTION MODELS B BC BV SERVICE MANUAL rr 1 DIES Pelo ae e Rochester BULLETIN 9D 2 MODELS B BC BV PAGE 2 P Delco W Rochester TYPICAL MODELS B BC BV B The basic Model B carburetor is a single bore downdraft type It is equipped with a manually op erated choke and is mainly used on truck applica tions The Model BC is the same basic unit except it has a fully automatic choke mounted on the air horn and is used for both passenger car and truck applications The Model BV unit uses a fully automatic choke however instead of the conventional choke piston and housing a vacuum operated diaphragm plunger is used The thermostatic coil is mounted on the ex haust manifold instead of the choke housing and is connected to the carburetor choke shaft by connect ing linkage Design features included in all of the above car buretor models are as follows A concentric type float bowl is used which allows fuel in the float bowl to completely surround the u B C GENERAL DESCRIPTION H Bv main carburetor bore and venturi The concentric float bowl design plus the centrally located main fuel discharge nozzle prevents fuel spill over during ab normal car maneuvers such as sharp turns quick starts and stops The main assembly is a detachable unit which con tains the main metering parts of the carburetor I2. Check floats for fuel leaks by shaking C Check throttle shaft bores for wear and out of round in the throttle bore area D Inspect idle adjusting needle for burrs or grooves and misalignment Such a condition requires replacement E Inspect pump plunger cup replace if worn or damaged F Inspect pump well in bowl for wear or scor ing G Check pump shaft and lever for excessive wea Always use new gaskets in reassembly Check filter element for dirt or lint Clean and if it is distorted or remains plugged replace If for any reason pressed in parts have become loose or damaged in the castings they must be replaced Check power piston stem for alignment replace if bent ASSEMBLY PROCEDURE Throttle Body Assembly Fig 14 I 2 If removed install throttle stop screw in throttle lever Screw idle mixture adjusting needle and spring into throttle body until it is finger tight Back needle out 114 turns as a temporary idle mixture adjustment using two screws and lockwashers Tighten screws evenly and securely Note Make sure holes in gasket line up with holes in throttle body Float Bowl Assembly Fig 13 e Install 3 16 steel ball into pump discharge cavity Carefully insert pump discharge spring and guide on top of ball Tap the discharge guide lightly to seat flush with the float bow casting Note The pump discharge guide is installed correctly when it is at right angles with the pum
3. choke system consists of a choke valve located in the air horn a vacuum break diaphragm unit fast idle cam choke linkage and a thermostatic coil which is located on the engine ex haust manifold The thermostatic coil is connected to the choke valve by a rod The choke operation is controlled by a combination of intake manifold vacuum the off set choke valve atmospheric tem perature and exhaust manifold heat The thermostatic coil located on the engine mani fold is calibrated to hold the choke valve closed when the engine is cold When starting the engine air velocity against the off set choke valve causes the valve to open slightly against the torque of the thermostatic coil When the engine is started manifold vacuum applied to the vacuum diaphragm unit mounted on the carburetor air horn will open the choke valve to a point where the engine will operate without loading or stalling The choke valve will remain in this position until the engine begins to warm up and the heat from the exhaust manifold warms the thermostatic coil to relax its tension and allows the choke valve to gradually open Open ing of the choke valve is controlled by air flow through the carburetor air horn past the off set choke valve and manifold heat acting upon the ther mostatic coil The operation of the BV choke system is the same as the Model BC choke system other than the features described MODELS B BC BV MAJOR SERVICE OPERATIONS Disassem
4. long nosed pliers remove pump discharge guide Pump discharge spring and Lei PI Ger steel ball may now be removed by inverting bowl T P RETAINER 3 Remove clips from pump link and then remove MAIN WELL GER FLOAT pump link from throttle lever and pump plunger ASSEMBLY rod POWER 4 Remove the pump plunger from the float bowl PISTON by pulling straight upward AIR HORN 5 Remove pump return spring from bottom of pum AIR HOR aa pring m of pump AIR HORN 6 Place carburetor bowl with suction tube if equipped over edge of flat surface and remove two throttle body attaching screws Throttle body and gasket may now be removed FILTER Throttle Body Disassembly Fig 14 FIGURE 12 6 Remove hex head power valve check ball retainer THROTTLE from bottom of support then remove power valve STOP SCREW spring and ball Note Use care when removing power valve so as not to lose small spring and ball 7 Remove screw at base of main well support then remove the main well support from the air horn 8 Remove power piston and power piston spring from air horn Note Do not remove idle pick up tube from air IDLE MIXTURE AD JUSTING horn as it is pressed in place If unit is gt NEEDLE AND SPRING equipped with anti bubble screen in main well support it should not be removed Clean and blow out with compressed air FIGURE 14 only 1 Remove idle mixture adjusting needle and spring 9 Remove air horn gasket 2 If necessary
5. moves up ward in its cylinder allowing fuel to flow through CHECK BALL PUMP DISCHARGE PASSAGE FIGURE 6 a slot in the side of the pump well into the pump well through the vapor check ball passage by passing the plunger head and on into the bottom of the pump well The pump discharge ball is seated at this time to prevent fuel and air from draining into the pump well from the pump discharge passage When the pump plunger is moved downward for acceleration the force of the stroke seats the vapor check ball in the pump plunger head to prevent fuel flow back into the float bowl Downward motion of the pump plunger forces fuel up through the dis charge passage and lifts the pump discharge check ball from its seat and then passes on through the pump jets into the venturi area where it strikes the side of the boost venturi atomizing the fuel with the air and is delivered to the engine The check ball inside the pump plunger head provides relief for any vapors which might form in the pump well during hot idle or hot soak The check ball is designed so that it can move up and down in its passage Normally the ball is down or unseated by gravity and fuel vapors forming in the bottom of the pump well are automatically vented into the fuel bowl and out the air horn vent Choke System Model BC Fig 7 The purpose of the choke system is to provide a richer mixture for cold engine starting and operation Mixture enrichmen
6. through the main metering BULLETIN 9D 2 MODELS B BC BY Delco I PAGE 4 Rochester Idle System Cont jet into the main well The fuel then travels up through the idle pick up tube and through the cross bar in the air horn Air is then bled into the idle fuel at the center of the cross bar through the two top bleeds and the main nozzle The air fuel mix ture then is picked up by the horizontal idle tube in the cross bar and metered through a calibrated restriction then passes on into the vertical down channel where it is further bled with air by an in ternal air bleed in the vertical channel in the top of the float chamber The air fuel mixture con tinues downward past the off idle discharge port where more air is picked up to mix with the fuel mixture and then passes out the idle needle hole below the throttle valve Here the fuel mixture mixes with air coming past the slightly open throttle valve and passes into the engine as a combustible idle mixture On some applications an anti bubble screen is used inside of the main fuel well The purpose of the anti bubble screen is to break up any vapor bubbles which might form in the main well during hot engine idle and disrupt proper fuel metering Off Idle Operation Fig 3 AIR BLEEDS IDLE VENT IDLE PASSAGE ANTI BUBBLE INTERNAL IDLE AIR BLEED TUBE OFF IDLE DISCHARGE PORT IDLE NEEDLE IDLE NEEDLE HOLE FIGURE 3 As the throttle valve is opened slig
7. to replace remove throttle stop screw from throttle lever Float Bowl Disassembly vg 13 Note Due to close tolerance fit of the throttle If unit has tube pressed into power piston vacuum valve in the bore of the throttle body do passage remove small O ring seal from around not remove the throttle valve or shaft from vacuum tube the throttle body o BULLETIN 9D 2 Delco WY MODELS B BC BV Rochester PAGE 9 Cleaning and Inspection 3 Using a new gasket attach throttle body to bowl Dirt gum water or carbon contamination in the carburetor moving parts are often responsible for unsatisfactory performance For this reason efficient carburetion depends upon careful cleaning and in spection while servicing L Thoroughly clean carburetor castings and metal parts in clean cleaning solvent CAUTION Pump plunger plastic parts and gaskets should never be immersed in carburetor cleaner Wash in clean Stoddard Solvent or equivalent Blow out all passages in castings dry with com pressed air and blow off all parts until they are dry Make sure all jets and passages are clean Do not use wires or drills for cleaning fuel pas sages or air bleeds Check all parts for wear If wear is noted defective parts must be replaced NOTE ESPECIALLY THE FOLLOWING A Check float needle and seat for wear If wear is noted the assembly must be replaced B Check float hinge pin for wear and float for dents or distortion
8. bly Cleaning Inspection and Assembly Procedure Disassembly of Choke BC Fig 9 CHOKE HOUSING 3 FITTING 3 RETAINING SCREWS FIGURE 9 1 Loosen 14 fitting on choke vacuum tube Push fitting and gasket seal downward on the tube 2 Remove three choke cover attaching screws and retainers Remove choke cover cover gasket and thermostatic coil assembly from carburetor 3 Remove baffle plate inside choke housing 4 Remove choke piston and lever assembly from inside choke housing by removing lever attach ing screw from center of choke shaft NOTE On older model carburetors the attach ing screw may be on opposite end of shaft On these units it will be necessary to remove the choke shaft as outlined in paragraph 2 of BC BV choke disassembly 5 The choke piston may be removed from the choke piston lever by shaking out the choke piston pin 6 Remove two choke housing attaching screws in side choke housing then remove choke housing from the air horn rr Delco W Rochester Disassembly of Vacuum Break Unit BV Fig 10 1 Remove vacuum hose from vacuum break housing at diaphragm unit and from pipe in throttle body 2 Remove choke shaft lever screw diaphragm side remove two diaphragm bracket screws and remove vacuum break diaphragm lever and link assembly RETAINING SCREW VACUUM BREAK UNIT INLET FILTER VACUUM HOSE FIGURE 10 Completion of Choke Disassembly BC an
9. d BV Fig 11 1 Remove fast idle cam attaching screw Then the fast idle cam and choke rod can be removed from the upper choke lever and collar assembly 2 To remove choke valve remove stake on the end of the choke valve screws with a file Then re move the two choke valve attaching screws from the choke shaft and pull upward on choke valve to remove from shaft Choke shaft and levers assembly can now be removed from air horn Note position of choke trip lever tang in relation to choke lever and collar assembly tang for ease in reassembly CHOKE HOUSING CHOKE VALVE INTERNAL VENT CHOKE CLEAN AIR TUBE CHOKE LEVER AND COLLAR CHOKE TRIP LEVER CHOKE ROD FAST IDLE CAM FIGURE 11 BULLETIN 9D 2 MODELS B BC BV PAGE 7 BULLETIN 9D 2 PR MODELS B BC BY uo Delco W Rochester Air Horn Disassembly Fig 12 PUMP PLUNGER 1 On units using fuel inlet filter remove fuel filter inlet nut and gasket Then remove filter filter PUMP DISCHARGE spring and gasket GUDE SPRING ei AND BALL 2 Remove four air horn attaching screws Lift air horn straight up from bowl so as not to damage float Place air horn inverted on a flat surface 3 Remove float hinge pin and lift float assembly from air horn Float needle may now be re moved 4 Remove float needle seat and gasket with tool POWER BT 3006 5 Remove main metering jet from bottom of main PASSAGE well support FIGURE 13 2 Using a pair of
10. d vacuum rises above a specific point the power piston is drawn to the up position and the spring loaded ball of the power valve closes There is no adjustment required for the power system The vacuum break passage which is drilled from the bore of the air horn to the power piston chamber serves to relieve any vacuum build up around the piston This vacuum if unrelieved will draw vapors rom the float bowl past the piston and down the vacuum passage into the manifold resulting in an overly rich mixture Pump System Fig 6 Extra fuel for smooth quick acceleration is sup plied by a double spring pump plunger Rapid open ing of the throttle valve as in the case where ac celerating from low speed causes an immediate in crease in air velocity in the carburetor venturi Since fuel is heavier than air it requires a short period of time to catch up with the air flow To avoid a leanness during this momentary lag the accelera tor pump furnishes a quantity of liquid fuel sprayed into the air stream to mix with the incoming air and Aa BULLETIN 9D 2 Delco W Rochester MODELS B BC BV PAGE 5 maintain the proper air fuel mixture The pump is operated by the combined action of two springs which are calibrated to move the plunger in such a manner that a sustained charge of fuel is delivered for smooth acceleration The pump is at tached by linkage to the throttle lever When the throttle valve is closed the pump plunger
11. eassembly ls Install air horn on bowl assembly being careful to lower the air horn straight down so that the BULLETIN 9D 2 A MODELS B BC BV PAGE 10 Delco M Rochester Carburetor Reassembly Cont 12 Install the choke rod to the fast idle cam and carefully insert the upper end of the choke rod floats will not be bent during installation into the upper choke lever The dog leg of the 2 Install four air horn to float bowl attaching rod must face towards the idle mixture adjust screws and tighten evenly and securely ing needle 3 On units equipped with fuel inlet filter install 13 Attach the fast idle cam to the throttle body filter gasket inside fuel inlet nut then install fil ter and relief spring filter element retaining in place with the fuel inlet nut and gasket Tighten securely Choke Assembly Model BC Fig 9 amp 11 d a ks Install choke housing to air horn with two Phillips screws Tighten screws evenly and securely Note Install choke vacuum tube fitting and packing over choke vacuum tube Engage tube in choke housing before assembling housing to air horn Tighten choke housing vacuum tube fitting Install choke lever and collar assembly on choke shaft Tang on choke lever should point towards air horn casting Assemble choke shaft into air horn from the throttle lever side Tang on the trip lever should be above the tang on the upper choke lever Install choke valve into the
12. g conditions As shown in Figure No 1 components of a typical float system are the inlet fitting and gasket fuel filter and gasket pressure relief spring needle valve and seat and the float It should be noted that the fuel filter design is not used on all applications On units using the inlet filter the fuel filter element is spring loaded This feature provides a pressure relief so that in the event the filter should become plugged the restriction will cause fuel pump pressure to over come the spring and allow fuel to by pass the filter As fuel is used from the float bowl the float drops downward and allows the float needle to come off its seat This allows fuel to flow into the float bowl from the fuel pump The fuel flow continues until the fuel level reaches the correct height set by the float level adjustment At this point the needle again seats and fuel flow ceases While the engine is running the float needle is continuously unseating and seating as fuel from the float bowl is used for engine operation m BULLETIN 9D 2 Delco W Rochester MODELS B BC BV PAGE 3 Float System Cont As shown in Figure No 1 three air vents are used for transmitting air pressure to the fuel in the float bowl Two external vents located in the air horn just beneath the air cleaner supply atmospheric pressure to the fuel in the float bowl and are used to remove fuel vapors which might disrupt engine operation during pr
13. htly and engine speed increases extra fuel is needed to combine with the additional air going by the throttle valve into the engine This fuel is supplied by the off idle discharge port This supplies the fuel to the engine until air velocity is high enough in the venturi area to obtain efficient metering from the main metering system Further opening of the throttle valve causes in creased air flow through the carburetor bore which causes pressure drop in the boost venturi sufficient to cause fuel delivery from the main nozzle It should be remembered however that idle port discharge does not cease at this transfer point but rather di minishes as the main nozzle discharge increases Thus the two systems interact and produce a smooth fuel flow at all engine speeds Main Metering System Fig 4 MAIN NOZZLE BOOST MAIN METERING JET FIGURE 4 When air flow is high enough to create enough pressure differential in the boost venturi for fuel flow to start from the main nozzle the transfer point has been reached and the carburetor starts metering from the main metering system The fuel passes through the main metering jet into the main well where it rises in the main well passage and idle pickup tube The fuel continues up the main well tube to the horizontal crossbar in the air horn and to the main discharge nozzle At this point air is bled into the fuel by the two air bleeds in the top of the crossbar channel The m
14. idle cam should face towards the idle speed screw Choke Assembly Model BV Fig 108 11 le Install upper choke lever and collar assembly on choke shaft Tang on the choke lever should point towards air horn casting Assemble choke shaft into air horn from the throttle lever side Tang on the trip lever should be above the tang on the choke lever and collar assembly Install choke valve into slot in the choke shaft RP trade mark should face upward Install two choke valve attaching screws To insure proper end clearance between the choke trip lever and choke rod lever move the choke shaft horizontally to obtain 020 clearance be tween the two levers Then tighten the two choke valve attaching screws securely and stake in place Install vacuum diaphragm unit and bracket to side of air horn retaining with two attaching screws Tighten securely Install choke shaft lever to end of choke shaft diaphragm side aligning flats on lever with flats on choke shaft Large side of lever will hang downward Install retaining screw in end of choke shaft and tighten securely Install connecting rod to vacuum break dia phragm plunger by rotating end of rod so squirt on rod enters notch in plunger ends of rod face inward Install other end of rod into slot in choke lever Install new clip in groove in rod end and pinch together Install the choke rod to the fast idle cam then carefully insert the upper end of the choke rod in
15. ix ture is then discharged through the main discharge nozzle into the boost venturi Here the air fuel mix ture mixes with additional air and moves to the main venturi of the carburetor and into the intake mani fold The calibration of the main metering jet and air bleeds in the crossbar maintain economical air fuel ratios throughout the main metering range There fore no adjustments are necessary in the main meter ing system Power System Fig 5 A vacuum operated power system is used in the carburetor to provide additional fuel for high speed operation or increased road load A direct manifold vacuum passage within the carburetor to the engine intake manifold connects to the power piston Under Power System Cont heavy engine load the manifold vacuum drops de creasing the vacuum pull on the power piston and the piston is forced downward by a spring above the power piston The power piston spring is cali brated to force the power piston downward at a given manifold vacuum approx 9 Hai POWER PISTON sPmNG POWER PISTON NNVACUUM PASSAGE PISTON POWER RESTRICTION POWER VALVE MAIN METERING JET FIGURE 5 The downward motion of the power piston un seats the spring loaded ball in the power valve as sembly Fuel passes around the ball in the base of the main well support A calibrated power restriction meters the fuel prior to joining the fuel from the main metering jet As the manifol
16. n opening of the choke valve Through application of exhaust manifold heat the thermo static coil relaxes gradually until the choke valve is fully open As the engine is accelerated during warm up the corresponding drop in manifold vacuum on the choke piston and reduced air flow against the off set choke valve allows the thermostatic coil to momentarily close the choke providing a richer mixture During warm up it is necessary to provide a faster idle to prevent engine stalling This is accomplished by a fast idle cam which is connected by a rod to a lever on the choke shaft The idle screw on the throttle lever contacts graduated steps on the fast idle cam to provide a faster idle than normal to prevent engine stalling during the warm up period When the engine is fully warm and the choke valve is wide open the fast idle cam rotates so the idle screw rests on the low step on the fast idle cam where normal curb idle is obtained If the engine becomes flooded during the starting period the choke valve can be partially opened manually to allow increased air flow through the car buretor This is accomplished by depressing the accelerator pedal to the floor The unloader pro jection on the throttle lever contacts the edge of the fast idle cam and in turn partially opens the choke valve The extra air leans out the fuel mixture enough so the engine will start Model BV Choke System Fig 8 ENGINE FIGURE 8 The Model BV
17. ng Pump Discharge Ball Pump Discharge Spring Pump Return Clip Choke Rod Choke Rod Pin Choke Rod Screw Cam Altaching Cam Fast Idle Float Bowl Assembly Gasket Throttle Body Idle Needle Spring ldie Needle Packing Choke Tube Nut Choke Tube Throttle Body Assembly Screw Throttle Body Spring ldle Stop Screw Screw idle Stop Gasket Throttle Body Vacuum Break Diaphragm Assembly Model BV Screw Link lever Choke Shaft Retainer Pin Vacuum Break Assembly Hose Vacuum Idle Vent Valve Assembly Delco A United Delco Line
18. olonged hot engine operation An internal vent tube located inside the air horn bore extends upward from the float bow to the base of the air cleaner to provide a balance between ex ternal and internal air pressures acting upon the fuel in the float bowl On some applications the external vents are re placed by an idle vent valve as shown below in Fig ure No 2 The vent valve is located directly over the pump plunger When the throttle valve is closed the top of the pump plunger opens the vent valve and allows fuel vapors to vent from the float bowl dur ing hot idle operation The vent valve automatically closes after the throttle valve has moved from the idle position into the off idle range Idle System Fig 2 IDLE VENT IDLE PASSAGE ANTI BUBBLE SCREEN E IDLE PICKUP TUBE IDLE NEEDLE THROTTLE IDLE NEEDLE HOLE FIGURE 2 At idle speeds the throttle valve is nearly closed so there is not enough air flow through the venturi to lift fuel from the float bowl To supply enough fuel for idle and off idle requirements an idle sys tem is used To make fuel flow manifold vacuum is applied directly to the fuel in the bowl from the idle needle hole and the off idle port as the throttle valve is gradually opened The idle system con sists of the idle pick up tube idle tube idle passage e bleeds idle mixture needle and idle discharge ole Atmospheric pressure acting on the fuel in the float bowl forces fuel
19. p discharge jet and Hush with top of casting Place pump return spring in pump well and bottom spring in well Install pump plunger assembly in bowl making sure not to curl pump plunger cup during in stallation Attach pump link to pump plunger rod and throttle lever using new clips Note Dog leg on pump link will face away from throttle shajt when installed correctly If unit is equipped with vacuum tube in power piston passage install O ring seal around power piston vacuum tube on top of inner bowl parting surface Air Horn Assembly Fig 12 1 2 Install float needle seat and gasket with tool BT 3006 Place new air horn gasket on top of air horn check to be sure that all air horn and gasket holes are in line Install power piston spring and power piston in vacuum cavity Note Piston should ride free in cavity Attach main well support to air horn assembly and tighten attaching screws securely Install power valve ball small steel ball power valve spring and retainer in main well support Tighten power valve retainer securely Check for free motion of power piston Install main metering jet in main well support Place float needle in float needle seat Place float carefully in position with drop tang pointing downward tawards air horn and install float hinge pin Make float adjustments as outlined in specifica tions and adjustment section of Parts and Serv ice Manual Carburetor R
20. slot of the choke shaft RP trade mark should face upward Install two choke valve attaching screws To insure proper end clearance between the choke trip lever and choke rod lever move the choke shaft horizontally to obtain 020 clear ance between the two levers Then tighten the two choke valve attaching screws securely and stake in place Assemble choke piston to the choke piston lever with small piston pin If there is a flat on head of piston it should face downward when installed correctly Install choke piston and lever assembly into choke housing by placing choke piston into the choke piston bore Align flats on the choke shaft with the flats on the choke piston lever Install attaching screw into the end of the choke shaft and tighten securely to retain choke piston lever to the choke shaft Install baffle plate into the choke housing Place new choke cover gasket onto the thermostatic coil and cover assembly and then install the coi to the choke housing Rotate the thermostatic cover and coil assembly until the tang on the thermostatic coil picks up the tang on the choke piston lever and begins to close the choke valve Keep rotating in this direction until the marks are aligned as specified in the specifications and adjustment section Install three retainers and attaching screws to the choke cover and housing Tighten securely assembly with the fast idle cam screw and tighten securely The steps on the fast
21. t is attached to the air horn and is easily removed for inspection and service It is suspended in the fuel in the float chamber which insulates it from heat which may be transmitted from the engine directly to the bottom of the float bowl This type design helps maintain more accurate fuel metering because less fuel vapors enter the main metering parts of the as sembly during hot engine operation The following text describes the functions of the six main carburetor systems for ease in trouble shooting and gives step by step procedures for proper servicing of the unit Copyright 1964 ROCHESTER PRODUCTS DIVISION GENERAL MOTORS CORP Printed in Canada a OPERATING SYSTEMS Float System Fig 1 SPRING FLOAT J FLOAT NEEDLE FLOAT FIGURE 1 All Model B carburetors use the conventional needle and seat to control fuel level in the float bowl With the concentric float bowl design dual pontoon floats are used to maintain a constant fuel level This is important as fuel level directly affects the air fuel ratio by determining the distance the fuel must rise to enter the nozzle for the idle and main metering systems A low fuel level will produce a leaner mix ture while a high fuel level will produce a richer mixture and possibly cause flooding The float bowl is designed so that the fuel is centrally located around the main well so that efficient carburetor metering can be maintained under all engine operat in
22. t is necessary because fuel vapor BULLETIN 9D 2 Es MODELS B BC BV Delco W Rochester Choke System Cont has a tendency to condense on cold engine parts such as the inside area of the intake manifold and cylinder head thereby decreasing the amount of combustible mixture available in the engine cylinder The Model BC choke system includes a thermo static coil choke housing choke piston choke valve fast idle cam and linkage It is controlled by a com bination of manifold vacuum air velocity against the offset choke valve and tension of the ther mostatic coil CHOKE COVER BAFFLE PLATE FIGURE 7 When the engine is cold tension of the ther mostatic coil holds the choke valve closed Starting the engine causes air velocity to strike the offset choke valve which tends to open it along with the action of intake manifold vacuum on the choke pis ton in the choke housing After the choke valve is opened to a predetermined position vacuum break the tension of the thermostatic coil balances against the force of air on the choke valve and the pull of the choke piston As the engine warms up the manifold vacuum which exists in the choke housing pulls hot air from the choke stove through an air passage in the choke housing to heat the thermostatic coil A baffle plate inside the choke housing next to the thermostatic coil serves to distribute heat evenly around the coil to prevent hot spots which would cause uneve
23. to the choke lever and collar assembly The dog leg of rod must face towards the idle mixture ad justing needle Attach the fest idle cam to the throttle body assembly with the fast idle cam screw and tighten securely The steps of the fast idle cam should face towards the idle speed screw Note Refer to specifications and adjustment sec tion of Parts and Service Manual or all adjust ment procedures and dimensions Mm Delco WY Rochester MODELS B BC BV TYPICAL ASSEMBLY 0 NO OC Q IM BULLETIN 9D 2 MODELS B BC BY PAGE 11 Screw Stat Cover Retainer Plain Retainer Toothed Stat Cover amp Coil Assembly Gasket Stat Cover Baffle Plate Screw Choke Housing Pin Choke Piston Choke Piston Choke Housing Fitting Fuel Inlet Gasket Fuel Inlet Gasket Fuel Inlet Filter Fuel Filter Spring Fuel Filter Screw Choke Lever Piston Lever amp Link Assembly Choke Shaft Assembly Choke Valve Screw Choke Valve Support Air Cleaner Screw Air Horn Air Horn Assembly Needle und Seat Assembly Spring Power Piston Piston Power Support Main Well Screw Main Well Support Main Metering Jet Power Valve Assembly Pin Float Hinge Float Assembly Gasket Air Horn Retainer Pump Assembly Spring Pump Duration Pump Plunger Assembly Retainer Pin Link Pump Guide Pump Discharge Spri
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