The best way to diagnose a bad carburetor is to eliminate all other possible sources of the problem. If the carburetor is suspected to be the problem, first perform all of the adjustments given in this section. If this doesn't correct the difficulty, then check the following. Check the ignition system to make sure that the spark plugs, breaker points, and condenser are in good condition and adjusted to the proper specifications. Examine the emission control equipment to make sure that all the vacuum lines are connected and none are blocked or clogged. See the first half of this section. Check the ignition timing adjustment. Check all of the vacuum lines on the engine for loose connections, slips or breaks. Torque the carburetor and intake manifold attaching bolts to the proper specifications. If, after performing all of these checks and adjustments, the problem is still not solved, then you can safely assume that the carburetor is the source of the problem.
Float and Fuel Level
- Remove the carburetor.
- Remove the float bowl cover.
- Place a 23 / 32 in. feeler gauge between the float arm and inlet needle and invert the carburetor.
- Tighten the seat screw to set the fuel level.
- Remove the feeler gauge.
- With the carburetor inverted, place an 11 / 64 in. gauge between the top of the float and the inside surface of the float chamber. The gauge should pass lightly between the float and the chamber. If not, bend the tab on the float arm to adjust it.
- Upright the carburetor. Slide a 3 / 16 in. gauge between the bottom of the float and float chamber. The gauge should pass lightly between the float and chamber. If not, adjust the float by bending the upright tang on the float lever.
- Install the float bowl cover using a new gasket.
- Install the carburetor using a new mounting gasket.
- Run the engine and check for leaks.
- Remove the carburetor air horn and gasket from the carburetor.
- Invert the air horn assembly, and check the clearance from the top of the float to the bottom of the air horn. Hold the air horn at eye level when gauging the float level. The float arm (lever) should be resting on the needle pin. Do not load the needle when adjusting the float. Bend the float arm as necessary to adjust the float level (clearance). Do not bend the tab at the end of the float arm, because it prevents the float from striking the bottom of the fuel bowl when empty.
- Turn the air horn over and hold it upright and let the float hang free. Measure the maximum clearance from the top of the float to the bottom of the air horn with the float gauge. Hold the air horn at eye level when gauging the dimension. To adjust the float drop, bend the tab at the end of the float arm.
- Install the carburetor air horn with a new gasket.
- Operate the engine until it reaches normal operating temperature. Place the vehicle on a level surface and stop the engine.
- Remove the carburetor air cleaner assembly.
- Remove the air horn attaching screws and the carburetor identification tag. Temporarily, leave the air horn and gasket in position on the carburetor main body and start the engine. Let the engine idle for a few minutes, then rotate the air horn out of the way and remove the air horn gasket to provide access to the float assembly.
- While the engine is idling, use a scale to measure the vertical distance from the top machined surface of the carburetor main body to the level of the fuel in the fuel bowl. The measurement must be made at least 1 / 4 in. (6mm) away from any vertical surface to assure an accurate reading, because the surface of the fuel is concave, being higher at the edges than in the center. Care must be exercised to measure the fuel level at the point of contact with the float.
- If any adjustment is required, stop the engine to minimize the hazard of fire due to spilled gasoline. To adjust the fuel level, bend the float tab contacting the fuel inlet valve upward in relation to the original position to raise the fuel level, and downward to lower it. Each time the float is adjusted, the engine must be started and permitted to idle for a few minutes to stabilize the fuel level. Check the fuel level after each adjustment, until the specified level is obtained.
- Assemble the carburetor in the reverse order of disassembly, using a new gasket between the air horn and the main carburetor body.
To perform a preliminary dry float adjustment on both the primary and secondary fuel bowl float assemblies, remove the fuel bowls and invert them allowing the float to rest on the fuel inlet valve and set assembly. the fuel inlet valve and seat can be rotated until the float is parallel with the fuel bowl floor (actually the top of the fuel bowl chamber inverted). Note that this is an initial dry float setting which must be rechecked with the carburetor assembled and on the engine to obtain the proper wet fuel level.
This carburetor has an externally adjustable needle and seat assembly which allows the fuel level to be checked and adjust without removing the carburetor from the engine.
- Run the engine with the vehicle resting on a level surface until the engine temperature has normalized.
- Remove the air cleaner assembly.
- Place a suitable container or an absorbent cloth below the fuel level sight plug in the fuel bowl.
- Stop the engine and remove the sight plug and gasket on the primary float bowl. The fuel level in the bowl should be at the lower edge of the sight plug hole, plus or minus 1 / 16 in.
- To adjust the fuel level, install the sight plug and gasket, loosen one on the lower fuel bowl retaining screws and drain the fuel from the bowl only if the level is too high. Loosen the lockscrew on top of the fuel bowl just enough to allow the adjusting nut to be turned. Turn the adjusting nut about 1 / 2 of a turn in to lower the fuel level and out to raise the fuel level. By turning the adjusting nut 5 / 32 of a turn, the fuel level will change 1 / 32 in. at the sight plug.
- Start the engine and allow the fuel level to stabilize. Check the fuel level as outlined in Step 4.
- Repeat the procedure for the secondary float bowl adjustment.
- Install the air cleaner assembly if no further adjustments are necessary.
- Remove the carburetor.
- Remove the air horn assembly and remove the gasket.
- Invert the air horn.
- Use a T-scale, made for 4300 series carburetors, to measure the distance between the flat surface of the free end of each float pontoon and the air horn casting surface.
- The float pontoons should just touch the T-scale. If one float is lower than the other, twist the float and lever assembly slightly to correct the condition.
- To adjust the float level, bend the tab which contacts the needle and seat assembly.
If a T-scale is not available, you can make your own adjusting tool. The accompanying illustrations show you exactly what to do. The fabrication illustration also shows you how to make a tab bending tool. To use the bending tool:
- To raise the float: insert the open end of the tool to the right side of the float lever tab and between the needle and float hinge. Raise the float lever off of the needle and bend the tab downward.
- To lower the float: insert the bending tool to the left of the float lever tab, between the needle and float hinge. Support the float lever and bend the tab upward.
- Remove the carburetor.
- Hold the secondary throttle plates closed.
- Turn the secondary throttle shaft lever stop screw out until the secondary throttle plates seat in the throttle bores.
- Turn the screw back in until the screw just touches the lever, then 3 / 8 turn more.
HOLLEY 1904 1-BBL., FORD 1100 AND 1101 1-BBL.
The fast idle is controlled by the idle adjusting screw bearing against the bottom of the choke cam and lever during idle or closed throttle conditions. The choke cam and lever opens the throttle slightly, through contact of the idle adjusting screw with the cam, as the manual choke position is selected. Higher engine idle speeds are automatically provided through contact of the idle adjusting screw with the cam. The curb idle must be adjusted correctly for the fast idle to be proper during application of the choke.CARTER YF 1-BBL.-1963-74 ENGINES
- Position the fast idle screw on the kickdown step of the fast idle cam against the shoulder of the high step.
- Adjust by bending the choke plat connecting rod to obtain the specified clearance between the lower edge of the choke plate and the carburetor air horn. Use a drill bit inserted between the lower edge of the choke plate and the carburetor air horn.
- With the engine at operating temperature, air cleaner removed and a tachometer attached according to the manufacturer's instructions, manually rotate the fast idle cam to the top or second step as specified while holding the choke plate fully open. Turn the fast idle adjustment screw inward or outward as required to obtain the specified speed.
- When setting the fast idle speed, all distributor vacuum and EGR controls must be disconnected and plugged to insure proper speeds during cold operation.
- Run the engine to normal operating temperature.
- Remove the air cleaner and attach a tachometer to the engine according to the manufacturer's instructions.
- Manually rotate the fast idle to the top step while holding the choke plate fully opened.
- Rotate the cam until the fast idle adjusting screw rests on the cam step specified on the underhood emissions sticker.
- Turn the fast idle speed adjusting screw to obtain the speed specified in the Tune-Up Charts.
AUTOLITE (MOTORCRAFT) 2100 AND 2150 2-BBL.
The fast idle speed adjustment is made in the same manner as for the Model YF carburetor, starting at Step 3.
To adjust the model 2100 fast idle cam clearance, follow the procedure given below:
- Rotate the choke thermostatic spring housing 90° in the rich direction.
- Position the idle speed screw on the high step of the cam.
- Depress the choke pulldown diaphragm against the diaphragm stop screw to place the choke in the pulldown position.
- While holding the choke pulldown diaphragm depressed, open the throttle slightly and allow the fast idle cam to fall.
- Close the throttle and check the position of the fast idle cam. The screw should contact the cam at the V mark on the cam.
- Adjust the fast idle cam adjusting screw to obtain the proper setting.
- Remove the spark delay valve, if so equipped, from the Distributor vacuum advance line, and route the vacuum line directly to the advance side of the distributor.
- Trace the EGR signal vacuum line from the EGR valve to the carburetor and if there is EGR/PVS valve or temperature vacuum switch located in the vacuum line routing, disconnect the EGR vacuum line at the EGR valve and plug the line.
- If not equipped with an EGR/PVS valve or temperature vacuum switch do not detach the EGR vacuum line.
- Trace the purge valve vacuum line from the purge valve located on the canister, to the first point where the vacuum line can be detached from the underhood hose routing. Disconnect the vacuum line at that point, cap the open port, and plug the vacuum line.
- With the engine running at normal operating temperature, the choke plate fully opened and the manual transmission in Neutral and the automatic transmission in Park, place the fast idle level on the 2nd or kickdown step of the fast idle cam.
- Adjust the fast idle screw to within 100 rpm of the specified speed given on the Vehicle Emission Control Decal.
- Reconnect all vacuum lines.
- Set the parking brake, put the transmission in Park or Neutral and run the engine up to operating temperature.
- Turn off the air conditioning and heater controls.
- Disconnect and plug the vacuum hoses at the air control valve and EGR valve and purge control valve.
- Place the transmission in the position specified on the underhood decal.
- If necessary, check and adjust the curb idle rpm.
- Place the transmission in Neutral or Park and rev the engine. Place the transmission in the specified position according to the underhood decal and recheck the curb idle rpm. Readjust if necessary.
- Connect an external vacuum source which provides a minimum of 10 in. Hg (33.8 kPa) of vacuum to the Vacuum Operated Throttle Modulator (VOTM) kicker.
- Place the transmission in the specified position.
- Adjust the VOTM (throttle kicker) locknut if necessary to obtain the proper idle rpm.
- Reconnect all vacuum hoses.
- Remove the air cleaner.
- Loosen the anti-stall dashpot locknut.
- With the choke plate open, hold the throttle plate closed (idle position), and check the clearance between the throttle lever and the dashpot plunger tip with a feeler gauge.
Choke Plate Pull-Down Clearance
- Insert a drill or gauge of the specified size between the choke plate and the inside of the air horn, and place the choke linkage in the full choke position.
- While maintaining the full choke position, adjust the nut on the choke connector (pulldown) rod to just contact the swivel on the cam lever.
- Remove the air cleaner. Remove the choke thermostatic spring housing from the carburetor.
- Bend a 0.026 in. (0.66mm) diameter wire gauge at a 90° angle approximately 1 / 8 in. (3mm) from one end. Insert the bent end of the gauge between the choke piston slot and the right hand slot in the choke housing. Rotate the choke piston lever counterclockwise until the gauge is snug in the piston slot.
- Exert a light pressure on the choke piston lever to hold the gauge in place, then use a drill gauge with a diameter equal to the specified clearance between the lower edge of the choke plate and the carburetor bore to check clearance.
- To adjust the choke plate pulldown clearance, bend the choke piston lever as required to obtain the specified setting. Remove the choke piston lever for bending to prevent distorting the piston link, causing erratic choke operation.
- Install the choke thermostatic spring housing and gasket. Set the housing to specifications.
- Remove the air cleaner.
- With the engine at normal operating temperature, loosen the choke thermostatic spring housing retainer screws and set the housing 90° in the rich direction.
- Disconnect and remove the choke heat tube from the choke housing.
- Turn the fast idle adjusting screw outward one full turn.
- Start the engine, then check for the specified clearance between the lower edge of the choke plate and the air horn wall.
- If the clearance is not within specification the diaphragm stop screw (located on the underside of the choke diaphragm housing) clockwise to decrease or counterclockwise to increase the clearance.
- Connect the choke heat tube and set the choke thermostatic spring housing to specifications. Adjust the fast idle speed to specifications.
- Set throttle on fast idle cam top step.
- Note index position of choke bimetallic cap. Loosen retaining screws and rotate cap 90° in the rich (closing) direction.
- Activate pulldown motor by manually forcing pulldown control diaphragm link in the direction of applied vacuum or by applying vacuum to external vacuum tube.
- Measure vertical hard gauge clearance between choke plate and center of carburetor air horn wall nearest fuel bowl.
Pulldown setting should be within specifications for minimum choke plate opening.
If choke plate pulldown is found to be out of specification, reset by adjusting diaphragm stop on end of choke pulldown diaphragm.
If pulldown is reset, cam clearance should be checked and reset if required.
After pulldown check is completed, reset choke bimetallic cap to recommend index position as specified in the Carburetor Specifications Chart. Check and reset fast idle speed to specifications if necessary.HOLLEY 4180C
- Remove the choke thermostat housing, gasket and retainer.
- Insert a piece of wire into the choke piston bore to move the piston down against the stop screw.
- Measure the gap between the lower edge of the choke plate and the air horn wall.
- Turn the adjustment screw to specifications.
- Reinstall the choke thermostat housing, gasket and retainer.
EXCEPT HOLLEY 4180C
Loosen the choke cap retaining screws just enough to turn the cap. Turn the cap until the notch in the cap aligns with the specified index line on the choke housing. See the charts in this section or your underhood specifications sticker.HOLLEY 4180C
This adjustment is preset and should not be changed.Accelerator Pump Lever
- Insert the roll pin in the lower hole (HI position in the lever stop hold).
- Position the throttle and choke linkage so that the throttle plate will seat in the throttle bore. Hold the throttle plates in the closed position. Position a gauge or drill of the specified thickness between the roll pin and the cover surface. Bend the accelerating pump actuating rod to obtain the specified gauge or drill clearance between the pump cover and the roll pin in the pump lever.
- Hold the primary throttle plates in the wide open position.
- Using a feeler gauge, check the clearance accelerator pump operating lever adjustment screw head and the pump arm while depressing the pump arm with your finger. The clearance should be 1 / 64 in. (0.015 in. or 0.381mm).
- To make an adjustment, hold the adjusting screw locknut and turn the adjusting screw inward to increase, or outward to decrease, the adjustment. 1 / 2 turn will change the clearance by 1 / 64 in.
Acceleration requirements in various climates are satisfied by controlling the amount of fuel discharged by the accelerating pump. The pump stroke is controlled by changing the location of the roll pin in the lever stop hole.
For operation in ambient temperatures 50°F (10°C) and below, place the roll pin in the hole of the pump operating lever marked HI (lower hole). For best performance and economy at normal ambient temperatures and high altitude, specifically above 50°F (10°C) and/or above 5000 ft. (1524 m), place the roll pin in the LO (upper hole) of the lever.MOTORCRAFT 2150
The accelerating pump stroke has been factory set for a particular engine application and should not be readjusted. If the stroke has been changed from the specified hole reset to specifications by following these procedures.
- To release the rod from the retaining clip, lift upward on the portion of the clip that snaps over the shaft and then disengage the rod.
- Position the clip over the specified hole in the overtravel lever and insert the operating rod through the clip and the overtravel lever. Snap the end of the clip over the rod to secure.
This adjustment is preset and should not be changed.Dechoke
EXCEPT HOLLEY 4180C AND MOTORCRAFT 4350
- Remove the air cleaner.
- Hold the throttle plate fully open and close the choke plate as far as possible without forcing it. Use a drill of the proper diameter to check the clearance between the choke plate and air horn.
- If the clearance is not within specification, adjust by bending the arm on the choke trip lever. Bending the arm downward will increase the clearance, and bending it upward will decrease the clearance. Always recheck the clearance after making any adjustment.
- If the choke plate clearance and fast idle cam linkage adjustment was performed with the carburetor on the engine, adjust the engine idle speed and fuel mixture. Adjust the dashpot (if so equipped).
- Hold the throttle plates in the wide open position.
- Rotate the choke plate downward towards the closed position until the pawl on the fast idle speed lever contacts the fast idle cam.
- Check the clearance between the lower edge of the choke plate and the air horn wall.
- Adjust the clearance as specified in the charts in this section, by bending the pawl on the fast idle speed lever forward to increase, or backward to decrease the clearance.
REMOVAL & INSTALLATION
- Remove the air cleaner.
- Remove the throttle cable or rod from the throttle lever. Disconnect the distributor vacuum line, EGR vacuum line, if so equipped, the inline fuel filter and the choke heat tube at the carburetor.
- Disconnect the choke clean air tube from the air horn. Disconnect the choke actuating cable, if so equipped.
- Remove the carburetor retaining nuts then remove the carburetor. Remove the carburetor mounting gasket, spacer (if so equipped), and the lower gasket from the intake manifold.
- Before installing the carburetor, clean the gasket mounting surfaces of the spacer and carburetor. Place the spacer between two new gaskets and position the spacer and gaskets on the intake manifold. Position the carburetor body flange, snug the nuts, then alternately tighten each nut in a crisscross pattern.
- Connect the inline fuel filter, throttle cable, choke heat tube, distributor vacuum line, EGR vacuum line, and choke cable.
- Connect the choke clean air line to the air horn.
- Adjust the engine idle speed, the idle fuel mixture and anti-stall dashpot (if so equipped). Install the air cleaner.
Efficient carburetion depends greatly on careful cleaning and inspection during overhaul since dirt, gum, water or varnish in or on the carburetor parts are often responsible for poor performance.
Overhaul the carburetor in a clean, dust free area. Carefully disassembly the carburetor, referring often to the exploded views. Keep all similar and look-alike parts segregated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.
When the carburetor is disassembled, wash all parts (except diaphragms, electric choke units, pump plunger and any other plastic, leather, fiber, or rubber parts) in clean carburetor solvent. Do not leave the parts in the solvent any longer than is necessary to sufficiently loosen the dirt and deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Rinse all parts in clean solvent and blow them dry with compressed air or allow them to air dry, while resting on clean, lint-free paper. Wipe clean all cork, plastic, leather and fiber parts with clean, lint free cloth.
Blow out all passages and jets with compressed air and be sure that there are no restrictions or blockages. Never use wire or similar tools to clean jets, fuel passages or air bleeds. Clean all jets and valves separately to avoid accidental interchange.
Examine all parts for wear or damage. If wear or damage is found, replace the defective parts. Especially, inspect the following:
- Check the float needle and seat for wear. If wear is found, replace the complete assembly.
- Check the float hinge pin for wear and the float(s) for dents or distortion. replace the float if fuel has leaked into it.
- Check the throttle and choke shaft bores for wear or an out-of-round condition. Damage or wear to the throttle arm, shaft or shaft bore will often require replacement of the throttle body. These parts require a close tolerance of fit; wear may allow air leakage, which could affect starting and idling.
- Inspect the idle mixture adjusting needles for burrs and grooves. Any such condition requires replacement of the needle, since you will not be able to obtain a satisfactory idle.
- Test the accelerator pump check valves. They should pass air one way, but not the other. Test for proper seating by blowing and sucking on the valve. Replace the valve as necessary. If the valve is satisfactory, wash the valve again to remove moisture.
- Check the bowl cover for warped surfaces with a straightedge.
- Closely inspect the valves and seats for wear and damage, replacing as necessary.
- After the carburetor is assembled, check the choke valve for freedom of operation.
Carburetor overhaul kits are recommended for each overhaul. these kits contain all gaskets and new parts to replace those which deteriorate most rapidly. Failure to replace all of the parts supplied with the kit (especially gaskets) can result in poor performance later.
Most carburetor manufacturers supply overhaul kits of three basic types: minor repair; major repair; and gasket kits.
After cleaning and checking all components, reassemble the carburetor, using new parts and referring to the exploded view. When reassembling, make sure that all screws and jets are right in their seat, but do not overtighten, as the tip will be distorted. Tighten all screws gradually, in rotation. Do not tighten needle valves into their seats; uneven jetting will result. Always use new gaskets. Be sure to adjust the float level.