Chrysler Full-Size Vans 1967-1988 Repair Guide

Carter Thermo-Quad

Print

ADJUSTMENTS



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Float level adjustment for the Thermo-Quad carburetor

Float Setting
  1. Remove the bowl cover and invert it.
  2.  
  3. Place the gasket on the cover and, with the floats resting on the needle check the distance from the gasket surface to the float bottom (now upside) on each float. The distance should be 27 / 32 ".
  4.  
  5. If not, bend the float lever arm.
  6.  

Never allow the float lever to depress the needle when measuring or adjusting!

Secondary Throttle Linkage

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Secondary throttle linkage adjustment for the Thermo-Quad carburetor

  1. Remove the carburetor.
  2.  
  3. Hold the fast idle lever in the curb idle position and invert the carburetor.
  4.  
  5. Slowly open the primary throttle plates. The primary and secondary levers should both contact the stops at the same time.
  6.  
  7. If an adjustment is necessary, bend the secondary throttle operating rod at the angle.
  8.  

Secondary Air Valve Opening

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: Secondary air valve opening adjustment on the Thermo-Quad carburetor

  1. With the air valve in the wide open, the gap between the air valve at the short side and the air horn should be 1 / 2 ".
  2.  
  3. If not, the corner of the air valve is notched for adjustment. Bend the corner with a needle-nosed pliers for proper adjustment.
  4.  

Secondary Air Valve Spring Tension

See Figure 4



Click image to see an enlarged view

Fig. Fig. 4: Secondary air valve spring tension adjustment on the Thermo-Quad

Hold the air valve adjustment plug with a screwdriver while loosening the lock plug to avoid the spring's snapping out of position. If the spring snaps out, you'll have to disassemble the carburetor!

  1. Loosen the air valve lock plug and allow the air valve to position itself in the wide open position.
  2.  
  3. Using a long screwdriver and tool C-4152 on the plug, turn the plug counterclockwise until the air valve contacts its stop lightly, then give it 1 1 / 4 turns more.
  4.  
  5. Hold the adjustment plug securely and tighten the lock plug with tool C-4152.
  6.  

Accelerator Pump Stroke

See Figure 5



Click image to see an enlarged view

Fig. Fig. 5: Accelerator pump stroke adjustment on the Thermo-Quad carburetor

FIRST STAGE
  1. Be sure that the throttle connector rod is in the center hole of the pump arm, or, on 2-hole arms, the inner hole.
  2.  
  3. Measure the height of the accelerator pump plunger link at curb idle. On trucks with a solenoid idle stop, the ignition switch should be in the ON position.
  4.  
  5. The height should be 1 / 2 ". If not, bend the throttle connector rod at the second angle from the top.
  6.  

SECOND STAGE
  1. Open the choke, then open the throttle until the secondary lockout latch is [cf2]just applied. Downward travel of the plunger stops at this point.
  2.  
  3. Measure the height of the pump plunger link. The height should be 5 / 16 ". If not, bend the tang at the bottom of the throttle lever.
  4.  

Choke Control Lever

See Figure 6



Click image to see an enlarged view

Fig. Fig. 6: Choke control lever adjustment on the Thermo-Quad

  1. Remove the carburetor.
  2.  
  3. Place the carburetor on a clean, flat surface with the surface flush with the bottom of the flange and extending out under the choke control lever.
  4.  
  5. Close the choke by pushing the lever with the throttle partially open.
  6.  
  7. Measure the vertical distance from the top of the rod hole in the control lever, down to the flat surface on which the carburetor is resting. The distance should be 3 3 / 8 ".
  8.  
  9. If not, bend the link connecting the two choke shafts at the upper angle.
  10.  

If you change this adjustment, you'll have to reset the vacuum kick, fast idle cam and choke unloader adjustments.

Choke Diaphragm Connector Rod

See Figure 7



Click image to see an enlarged view

Fig. Fig. 7: Thermo-Quad choke diaphragm connector adjustment

  1. Using a vacuum source, or by hand, fully depress the diaphragm stem.
  2.  
  3. With light opening pressure on the air valve connector rod, check the gap between the air valve and its stop. The gap should be 0.040".
  4.  
  5. If not, bend the diaphragm control rod at its angle.
  6.  

If you change this setting, you'll have to adjust the vacuum kick.

Choke Vacuum Kick

See Figure 8



Click image to see an enlarged view

Fig. Fig. 8: Choke vacuum kick adjustment on the Thermo-Quad carburetor

  1. Remove the carburetor.
  2.  
  3. Using a vacuum source, or by hand, fully depress the vacuum diaphragm plunger.
  4.  
  5. Using a 0.160" drill bit for 49 states and Canada, or 0.100" for California, measure between the lower edge of the choke plate and the air horn wall at a point close to the outboard end.
  6.  
  7. Adjustment will be necessary if a slight drag is not felt. Bend the tang on the diaphragm rod operating lever to adjust the gap.
  8.  

Fast Idle Cam Position

See Figure 9



Click image to see an enlarged view

Fig. Fig. 9: Fast idle cam position adjustment on the Thermo-Quad carburetor

  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position with light pressure on the choke linkage.
  2.  
  3. Insert a 0.100" drill bit between the lower edge of the choke plate and the wall of the air horn.
  4.  
  5. If adjustment is necessary, bend the fast idle link at the angle until the specified drill fits between the choke plate and the wall of the air horn.
  6.  

When this adjustment is made, the choke unloader adjustment and secondary throttle lockout adjustment must be reset.

Choke Unloader

See Figure 10



Click image to see an enlarged view

Fig. Fig. 10: Choke unloader adjustment on the Thermo-Quad carburetor

  1. Hold the throttle valves in the wide open position.
  2.  
  3. Insert a 0.310" drill bit between the lower edge of the choke valve and the wall of the air horn.
  4.  
  5. With a finger pressing lightly against the choke plate, a slight drag should be felt as the drill is being withdrawn.
  6.  
  7. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  8.  

Secondary Throttle Lockout

See Figure 11



Click image to see an enlarged view

Fig. Fig. 11: Secondary throttle lockout adjustment on the Thermo-Quad carburetor

  1. Move the fast idle control lever to the open choke position.
  2.  
  3. Measure the clearance between the lockout lever and the stop. The gap should be 0.060-0.090".
  4.  
  5. If not, bend the tang on the fast idle control lever.
  6.  

Fast Idle Speed

See Figure 12



Click image to see an enlarged view

Fig. Fig. 12: Fast idle speed adjustment on the Thermo-Quad

  1. Run the engine to normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly. Remove the air cleaner and disconnect the vacuum lines to the heated air control and the OSAC (Orifice Spark Advance Control) valve. If there is no OSAC valve, disconnect the distributor vacuum advance line. Disconnect the EGR hose. Cap all carburetor vacuum fittings.
  4.  
  5. Close the throttle plates until the fast idle screw can be positioned on the second highest speed step of the cam.
  6.  
  7. Start the engine. Adjust the idle speed and mixture, if necessary.
  8.  
  9. Turn the fast idle speed screw in or out until 1,700 rpm is obtained.
  10.  
  11. Stopping the engine between adjustments is not necessary. However, be sure to position the fast idle speed screw on the cam after each speed adjustment.
  12.  

Vacuum Throttle Positioner
  1. Run the engine to normal operating temperature.
  2.  
  3. With the transmission in Neutral and the brakes applied, accelerate the engine to above 2,000 rpm. Note that the vacuum positioner unit operates and can withstand a hand-applied load in the operating position. If not, replace the positioner.
  4.  
  5. Accelerate the engine, by hand-moving the linkage, to 2,500 rpm.
  6.  
  7. Loosen the positioner adjustment locknut and rotate the positioner assembly until the positioner just contacts the throttle lever.
  8.  
  9. Release the throttle lever and slowly adjust the positioner to decrease the engine speed until a sudden drop in engine speed occurs, above 1,000 rpm. At this point, continue turning the positioner, in the decreasing direction, an additional 1 / 4 turn. Hold the positioner and tighten the locknut.
  10.  
  11. Accelerate the engine, by hand, to 2,500 rpm and release the throttle. The engine should return to normal idle.
  12.  

 
label.common.footer.alt.autozoneLogo