Jeep Wagoneer/Commando/Cherokee 1984-1998

Carter YFA Feedback Carburetor

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The Carter model YFA feedback carburetor was used on the 2.5L engine.

DESCRIPTION



The Carter/Weber YFA carburetor consists of three main assemblies. The air horn contains the choke, vacuum break, choke plate duty cycle solenoid, float and assembly. The main body contains the pump diaphragm assembly, metering jet, low-speed jet, accelerator pump check ball and weight, pump bleed valve and wide open throttle switch. The throttle body contains the throttle plate, throttle shaft and lever, idle mixture screw with O-ring and a tamper-proof plug.

The duty cycle solenoid is an integral part of the YFA carburetor. The control unit operates the duty cycle solenoid to provide the proper air/fuel ratio by controlling the air flow. In open loop operation, the air supplied by the duty cycle solenoid is preprogrammed. In closed loop operation, the control unit signals the duty cycle solenoid to provide additional air to the air/fuel mixture depending upon the sensor inputs to the control unit. Air from the duty cycle solenoid is then distributed to the carburetor idle circuit and main metering circuit where it mixes with the fuel.

ADJUSTMENTS



Fast Idle Speed

See Figure 1

  1. Disconnect and plug the EGR valve vacuum hose at the valve.
  2.  
  3. Connect a tachometer to the ignition coil negative (TACH) terminal.
  4.  
  5. Place the automatic transmission in Park, or the manual transmission in Neutral, then start the engine and allow it to reach normal operating temperature.
  6.  
  7. Position the fast idle speed adjustment screw on the second step of the fast idle cam.
  8.  
  9. Turn the fast idle adjustment screw to obtain a fast idle speed of 2300 rpm (automatic transmission) or 2000 rpm (manual transmission). If the fast idle speed listed on the underhood emission sticker differs from the above, use the specification on the underhood sticker.
  10.  
  11. Allow the throttle to return to curb idle speed, then reconnect the EGR valve vacuum hose. Turn the ignition OFF and disconnect the tachometer.
  12.  



Click image to see an enlarged view

Fig. Fig. 1: Cater YFA fast idle adjustment screw (1)

Sole-Vac Vacuum Actuator

See Figure 2

  1. Connect a tachometer to the ignition coil TACH terminal.
  2.  
  3. Start the engine and allow it to reach normal operating temperature.
  4.  
  5. This adjustment is made with the automatic transmission in Drive or manual transmission in Neutral and all accessories turned OFF .
  6.  
  7. Disconnect the vacuum hose from the Sole-Vac vacuum actuator and plug. Connect an external vacuum source and apply 10-15 in. Hg (34-51 kPa) of vacuum to the actuator.
  8.  
  9. Adjust the idle speed to 850 rpm (auto. trans.), 950 rpm (manual trans.) using the vacuum actuator adjustment screw on the throttle lever. Use the specifications on the underhood sticker if they differ from the specifications.
  10.  
  11. Turn the ignition OFF and disconnect the tachometer and vacuum pump. The Sole-Vac curb idle speed should be adjusted following this procedure.
  12.  



Click image to see an enlarged view

Fig. Fig. 2: Sole-Vac adjustment screw location (2)

Curb Idle Speed

See Figure 3

  1. Connect a tachometer to the ignition coil TACH terminal.
  2.  
  3. Place the automatic transmission in Drive, or the manual transmission in Neutral.
  4.  
  5. Start the engine and allow it to reach normal operating temperature.
  6.  
  7. Disconnect and plug the vacuum hose from the actuator.
  8.  
  9. Adjust the hex head curb idle speed adjustment screw to 700 rpm (auto. trans.) or 750 rpm (manual trans.). Use the specifications on the underhood sticker if they differ from the above specifications.
  10.  
  11. Turn the ignition switch OFF , then disengage the tachometer and reconnect the vacuum actuator hose.
  12.  



Click image to see an enlarged view

Fig. Fig. 3: Curb idle speed adjustment screw location (3)

Float Level

See Figure 4

  1. Remove and invert the air horn assembly and check the clearance from the top of the float to the surface of the air horn with a T-scale.
  2.  
  3. The air horn should be held at eye level when gauging and the float arm should be resting on the needle pin.
  4.  
  5. Do not exert pressure on the needle valve when measuring or adjusting the float. Bend the float arm as necessary to adjust the float level.
  6.  


CAUTION
Do not bend the tab at the end of the float arm as it prevent the float from striking the bottom of the fuel bowl when empty and keeps the needle in place.



Click image to see an enlarged view

Fig. Fig. 4: Carter YFA carburetor float level measurement

Float Drop
  1. Hold the air horn upright and let the float hang freely.
  2.  
  3. Measure the maximum clearance from the toe end of the float to the casting surface.
  4.  
  5. Hold the air horn at eye level when measuring To adjust, bend the tab at the end of the float arm.
  6.  

Metering Rod

See Figure 5

  1. Remove the air horn. Back out the idle speed adjusting screw until the throttle plate is seated fully in its bore.
  2.  
  3. Press down on the upper end of the diaphragm shaft until the diaphragm bottoms in the vacuum chamber.
  4.  
  5. The metering rod should contact the bottom of the metering rod well. The lifter link at the outer end nearest the springs and at the supporting link should be bottomed.
  6.  
  7. Turn the rod adjusting screw until the metering rod just bottoms in the body casting. For final adjustment, turn the screw one additional turn clockwise.
  8.  
  9. Install the carburetor air horn and replacement gasket on the carburetor, then set the curb idle speed to specifications.
  10.  



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Fig. Fig. 5: Carter YFA metering rod adjustment

Fast Idle Cam Index

See Figure 6

  1. Put the fast idle screw on the second highest step of the fast idle cam, against the shoulder of the high step.
  2.  
  3. Measure the clearance between the lower edge of the choke valve and the air horn wall. It is not necessary to remove the air cleaner bracket when measuring clearance between the choke valve and air horn wall, position the gauge next to the bracket.
  4.  
  5. Adjust by bending the choke plate connecting rod to obtain the specified clearance between the lower edge of the choke plate and the air horn wall.
  6.  



Click image to see an enlarged view

Fig. Fig. 6: Fast idle cam index adjustment. (D) is the adjusting screw; (E) is the second step of the cam (F)

Choke Unloader

See Figure 7

  1. Hold the throttle lever fully open and apply pressure on the choke valve toward the closed position.
  2.  
  3. Measure the clearance between the lower edge of the choke valve and the air horn wall. See the Specifications Chart.
  4.  

DO NOT bend the unloader tang DOWN.

  1. Adjust by bending the unloader tang which contacts the fast idle cam. Bend toward the cam to increase clearance, away to decrease.
  2.  
  3. Ensure the unloader tang is at least 0.070 in. (1.8mm) from the main body flange when the throttle is open.
  4.  
  5. Check for full throttle opening when throttle is operated from inside vehicle.
  6.  



Click image to see an enlarged view

Fig. Fig. 7: Choke unloader adjustment. (H) is the throttle lever; (J) is the unloader tang; (K) is the cam; (L) is the gap

Automatic Choke

See Figure 8

  1. Loosen the choke cover retaining screws, then turn the choke cover so that the index mark on the cover lines up with the specified mark on the choke housing.
  2.  



Click image to see an enlarged view

Fig. Fig. 8: Choke cover assembly

Choke Plate Pulldown
PISTON-TYPE CHOKE

See Figure 9

  1. Remove the air cleaner assembly.
  2.  
  3. Check choke cap retaining ring rivets to determine if mandrel is well below the rivet head. If mandrel appears to be at or within the rivet head thickness, drive it down or out with a 1 / 16 in. (1.5mm) diameter punch.
  4.  
  5. Use a 1 / 8 in. (3mm) diameter drill for drilling the rivet heads. Drill into the rivet head until the rivet head comes loose from the rivet body.
  6.  
  7. After the rivet head is removed, drive the remaining portion of the rivet out of the hole with a 1 / 8 in. (3mm) diameter punch.
  8.  

This procedure must be followed to retain the hole size.

  1. Repeat Steps 1-4 for the remaining rivet.
  2.  
  3. Remove screw in the conventional manner.
  4.  
  5. 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 shut in the piston slot.
  6.  
  7. Apply light pressure on the choke piston lever to hold the gauge in place, then measure the clearance between the lower edge of the choke plate and the carburetor bore using a drill with the diameter equal to the specified pulldown clearance.
  8.  
  9. Bend the choke piston lever to obtain the proper clearance.
  10.  
  11. Install choke cap gasket.
  12.  
  13. Install the locking and indexing plate.
  14.  
  15. Install the notched gasket.
  16.  
  17. Install choke cap, making certain that bi-metal loop is positioned around choke lever tang.
  18.  
  19. While holding cap in place, actuate choke plate to make certain bi-metal loop is properly engaged with lever tang. Set retaining clamp over choke cap and orient clamp to match holes in casting (holes are not equally spaced). Make sure retaining clamp is not upside down.
  20.  
  21. Place a 1 / 8 in. diameter x 1 / 2 in. long x 1 / 4 in. diameter head (3mm x 12.7mm x 6mm) rivet into the rivet gun and trigger lightly to retain the rivet.
  22.  
  23. Press rivet fully into casting after passing through retaining clamp and pop rivet (mandrel breaks off).
  24.  
  25. Repeat this step for the remaining rivet.
  26.  
  27. Install screw in conventional manner. Tighten to 17-20 inch Ibs. (2-2.2 Nm).
  28.  



Click image to see an enlarged view

Fig. Fig. 9: Removing the choke connector link

DIAPHRAGM-TYPE CHOKE
  1. Activate the pull-down motor by applying an external vacuum source.
  2.  
  3. Close the choke plate as far as possible without forcing it.
  4.  
  5. Using a drill of the specified size, measure the clearance between the lower edge of the choke plate and the air horn wall.
  6.  
  7. If adjustment is necessary, bend the choke diaphragm link as required.
  8.  

Choke Plate Clearance (Dechoke)
  1. Remove the air cleaner assembly.
  2.  
  3. 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.
  4.  
  5. If the clearance is not within specification, adjust by bending the arm on the choke lever of the throttle lever. Bending the arm downward will decrease the clearance, and bending it upward will increase the clearance. Always recheck the clearance after making any adjustment.
  6.  

Mechanical Fuel Bowl Vent
  1. Start the engine and wait until it has reached normal operating temperature before proceeding.
  2.  
  3. Check engine idle rpm and set to specifications.
  4.  
  5. Check DC motor operation by opening throttle off idle. The DC motor should extend.
  6.  
  7. Release the throttle, and the DC motor should retract when in contact with the throttle lever.
  8.  
  9. Disconnect the idle speed motor in the idle position.
  10.  
  11. Turn engine OFF .
  12.  
  13. Open the throttle lever so that the throttle lever actuating lever does not touch the fuel bowl vent rod.
  14.  
  15. Close the throttle lever to the idle set position and measure the travel of the fuel bowl vent rod at point A. The distance measured represents the travel of the vent rod from where there is no contact with the actuating lever to where the actuating lever moves the vent rod to the idle set position. The travel of the vent rod at point A should be 0.100-0.150 in. (2.5-3.8mm).
  16.  
  17. If adjustment is required, bend the throttle actuating lever at notch shown.
  18.  
  19. Reconnect the idle speed control motor.
  20.  

Secondary Throttle Stop Screw

Back off the screw until it does not touch the lever. Turn the screw in until it touches the lever, then turn it an additional 1 / 4 turn.

Removal & Installation



  1. Remove the air cleaner.
  2.  
  3. Tag and disconnect all hoses leading to the carburetor.
  4.  
  5. Disconnect the control shaft from the throttle lever.
  6.  
  7. Disengage the inline fuel filter, pullback spring and all electrical connectors.
  8.  
  9. Remove the carburetor mounting nuts and lift off the carburetor.
  10.  
  11. Remove the carburetor mounting gasket from the spacer.
  12.  

To install:
  1. Clean all gasket mating surfaces on the spacer and carburetor.
  2.  
  3. Install a new gasket on the spacer, then install the carburetor and secure it with the mounting nuts.
  4.  
  5. Engage all vacuum hoses, fuel lines and electrical connectors.
  6.  
  7. Connect the control shaft and pullback spring.
  8.  
  9. Install the air cleaner and adjust the curb and fast idle speed, as previously described.
  10.  

 
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