Main diaphragm block
Note: Before starting work, see Chapter 2. A new star bracket must be used when installing the diaphragm unit. Check the vacuum chambers as described in Chapter 16 point 1.
Removal
1. Proceed as described in Chapter 17, points 1 and 2.
2. Disconnect the vacuum tubes from the diaphragm assembly.
3. Use a punch to knock out the cylindrical pin securing the diaphragm block to the top cover of the carburetor.
4. Note the position of the bimetallic casing alignment marks, if necessary, make marks yourself to facilitate installation, then unscrew the three fastening screws and remove the bimetallic casing. Move the casing to the side, then be careful not to deform the coolant hoses or the electrical wiring of the throttle valve heater.
5. Remove the three screws securing the choke assembly to the carburetor body. Allow the choke assembly to drop down, but do not disconnect the choke linkage.
6. Remove the star bracket that secures the diaphragm assembly to the carburetor top cover and remove the diaphragm assembly.
Installation
7. Reinstall in reverse order, but use a new star-shaped clamp securing the diaphragm assembly to the carburetor top cover. Before installing the air box on top of the carburetor, check and, if necessary, adjust the pull-down valve as follows.
Vacuum pull-down
Adjustment
8. After removing the air filter or air block from the top of the carburetor as described in Chapter 17 point 2, proceed as follows.
9. Note the position of the bimetallic casing alignment marks to facilitate installation, if necessary, make marks yourself, then unscrew the three fastening screws, and remove the bimetallic casing. Move the casing to the side, then make sure that the coolant hoses or the throttle heater wiring are not deformed.
10. Place the fast idle speed adjusting screw at the highest notch of the fast idle cam and check that the choke is closed.
11. Move the pull-down lever toward the diaphragm block by pressing the adjustment screw until you feel resistance. Lock the lever in this position.
12. Using a drill of the appropriate diameter, measure the gap between the bottom of the valve and the wall of the primary chamber (see illustrations). Check that the clearance is as given for the "small" pull-down valve clearance in the Specifications.
13. If adjustment is necessary, turn the adjusting screw in the appropriate direction until the correct clearance is set.
14. Now push the pull-down lever towards the diaphragm block as far as it will go and lock the lever in this position.
15. As before, measure the gap between the underside of the throttle body and the primary chamber wall. Check that the gap is as given for the "large" pull-down throttle body clearance in the Specifications.
16. If adjustment is necessary, turn the adjusting screw in the appropriate direction until the correct clearance is set.
17. Connect the bimetallic spring to the throttle lever, place the bimetallic casing on the throttle casing, and loosely install the fastening screws. Align the marks on the bimetallic casing and the throttle casing as noted before removal, then tighten the fastening screws.
18. Install the air block on top of the carburetor.
Secondary pull-down winding
Removal
19. This unit works in conjunction with the main diaphragm unit.
20. To remove the winding, first proceed as described in Chapter 17 points 1 and 2.
21. Disconnect the diaphragm block vacuum tube.
22. Disconnect the wiring harness, then remove the mounting screw and remove the winding block and mounting bracket from the carburetor. Note that the mounting screw also secures the ground loop of the wiring harness connector (see illustration).
Installation
23. Perform the installation in the reverse order, but do not forget to secure the ground loop under the pull-down winding bracket mounting screw.
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