The Mazda Rotary Pick-Up uses a 4-barrel downdraft carburetor, while the piston engines use 2-barrel downdraft units.
ADJUSTMENTS Float and Fuel Level
1,586cc, 1,796cc AND 1,970cc ENGINES
See Figures 1, 2 and 3
- With the engine running, check the fuel level in the sight glass (in the fuel bowl).
- If the fuel level is not at the specified mark on the sight glass, remove the carburetor from the truck.
- Remove the fuel bowl cover.
- Invert the carburetor and lower the float until the tang on the float just contacts the needle valve.
Measure the clearance between the float and the edge of the bowl. Clearance should be:
1,586cc0.65mm (0.0256 in.)
- If the clearance is not as specified, bend the float seal lip until the proper clearance is obtained.
Turn the carburetor right side up and measure the clearance between the bottom of the float and the bowl. Clearance should be:
1,586cc and 1,796cc1.2mm (0.0472 in.)
- If not, bend the float stopper until the correct clearance is obtained.
- Install the fuel bowl cover.
- Reinstall the carburetor on the truck.
- Recheck the fuel level at the sight glass.
See Figures 4 and 5
- Remove the air horn from the carburetor.
- Turn the air horn upside down on a level surface. Allow the float to hang under its own weight.
- Measure the clearance between the float and the air horn gasket surface. The gap should be 11.5-12.5mm (0.4528-0.4921 in.). If not, bend the float seat lip to obtain the correct gap.
- Turn the air horn right side up and allow the float to hang under its own weight.
- Measure the gap between the BOTTOM of the float and the air horn gasket surface. The gap should be 46.0-47.0mm (1.811-1.850 in.). If not, bend the float stopper until it is.
Float LevelROTARY ENGINE
See Figures 6 and 7
- With the engine running, check the fuel level in the sight glass, using a mirror.
- If the fuel levels are not within the specified marks on the sight glass, remove the air horn with the floats.
- Invert the air horn and let the float hang so that it just contacts the needle valve.
- Measure the clearance between the float and the air horn gasket, which should be 1.1mm (0.0433 in.). Bend the float seat lip to adjust the clearance if necessary.
- Install the air horn and recheck the fuel levels in the sight glass.
Float DropROTARY ENGINE
See Figures 8 and 9
- Remove the air horn with the floats and allow the floats to hang free.
- Measure the clearance between the bottom of the float and the air horn gasket. The clearance should be 51.5-52.5mm (2.028-2.067 in.).
- If not, adjust the distance by bending the float stopper.
- Install the air horn and recheck the fuel level in the sight glass.
Fast Idle1,586cc ENGINE
See Figure 10
The fast idle can be adjusted by turning the fast idle adjusting screw. Check the choke plate for free operation.1,796cc ENGINE
See Figure 11
- Remove the air cleaner.
- With the choke plate fully closed, measure the clearance between the primary throttle plate and the wall of the throttle bore. The clearance should measure 1.6-1.7mm (0.0629-0.0669 in.) through 1976, and 1.8mm (0.0708 in.) in 1977-78, or 2.5mm (0.0984 in.) for 1977-78 California models.
- If the clearance is not as specified, bend the fast idle lever where it contacts the throttle lever tang until the proper clearance is obtained.
- Install the air cleaner.
See Figure 12
- Close the choke fully.
- Place the fast idle adjusting screw on the first step of the fast idle cam.
- Check the clearance between the throttle plate and the inside of the throttle wall (G) with a wire feeler gauge. It should measure 1.3-1.5mm (0.0512-0.0590 in.).
- If the clearance is incorrect, adjust by means of the fast idle screw, clockwise to increase or counterclockwise to decrease.
See Figures 13 and 14
- Set the fast idle cam so that the fast idle lever rests on the second step of the cam.
- Adjust the clearance between the air horn wall and the lower edge of the throttle plates, (G) by turning the fast idle adjusting screw. Clearance should be 0.75-1.13mm (0.0295-0.0445 in.)
See Figure 15
- Pull the choke knob all the way out.
- Measure the clearance between the primary throttle plate and the wall of the primary throttle bore. The clearance can be measured with a suitable drill bit.
- The clearance should be 1.0-1.3mm (#61-#55 drill) for trucks with manual transmission, or 1.2-1.5mm (#55-#53 drill) for trucks with automatic transmission.
- If the clearance is not as specified, adjust the fast idle by bending the connecting rod to obtain the proper clearance.
Accelerator Linkage1,586cc ENGINE
Inspect the throttle linkage for free operation. Remove the air cleaner. With the accelerator fully depressed, the position of the throttle plates should be vertical.1,796cc AND 1,970cc ENGINES
- Loosen the locknuts on the longer linkage rod and rotate both ends in the sockets until the proper accelerator travel from idle to wide-open throttle is obtained.
- Tighten the locknuts to set the adjustment.
See Figures 16 and 17
- Check the cable deflection at the carburetor. Deflection should be 1.0-3.0mm (0.0394-0.1181 in.). If not, adjust it by turning the adjusting nut at the bracket near the carburetor.
- Depress the accelerator pedal to the floor. The throttle plates should be vertical. If not, adjust their position by turning the adjusting nut on the accelerator pedal bracket.
Secondary Throttle ValveALL MODELS
See Figure 18
The clearance between the primary throttle valve and the air horn wall, when the secondary throttle valve just starts to open should be:
If not, bend the fast idle link (1972-84) or the tab B (1986 illustrated).
Vacuum Pulldown1976-78 VEHICLES
See Figure 19
- On California Mazdas, unplug the electrical connectors from the water thermo switch and connect a jumper wire between the connectors. Turn the ignition switch on.
- Pull the choke knob out to fully close the choke.
- Disconnect the vacuum source to the pulldown diaphragm.
- Connect an external vacuum source to the pulldown diaphragm. Gradually apply vacuum. The pulldown should start to operate (open the choke) at 5.9-7.5 in.Hg.
- Increase the vacuum to 9.8-12.0 in.Hg. Check the clearance between the carburetor air horn wall and the choke plate using a wire gauge. The clearance should measure 1.5-2.0mm (0.059-0.787 in.) for 1976; 1.6-1.9mm (0.063-0.075 in.) for 1977-78.
- Adjust the clearance if necessary by bending the pulldown connecting rod.
Choke1,586cc AND 1,796cc ENGINES
See Figure 20
- Push the choke knob all the way in.
- Loosen the choke cable attaching screws at the choke lever and the choke cable bracket.
- Be sure that the choke plate is fully open.
- Insert the choke cable into the choke lever. Tighten the attaching screw.
- Pull the cable outward to remove all slack between the choke lever and choke cable bracket and tighten the attaching screw at the choke cable bracket.
- Operate the choke to be sure that there is no binding and that it is operating properly.
There are four adjustments to be made to the choke in these years; choke/throttle valve opening adjustment; choke diaphragm adjustment; choke unloader adjustment; and choke thermostat (bi-metal) adjustment.
Choke/Throttle Valve Opening Angle See Figure 21
- Adjust the fast idle cam as previously outlines before making this adjustment.
- Place the fast idle screw on the second step of the fast idle cam.
- Measure the clearance between the edge of the choke plate and the throttle bore with a wire gauge. Clearance should be 0.4-0.7mm (0.0157-0.0276 in.).
- If the clearance is incorrect, adjust by bending the starting arm. If a large adjustment is required, the choke rod can be bent slightly.
Choke Diaphragm See Figure 22
- Remove the vacuum hose from the choke diaphragm. Attach a vacuum pump to the diaphragm fitting and apply approximately 15.6 in. Hg to the diaphragm.
- Check to see that the fast idle screw is on the first step of the fast idle cam.
- Press on the choke plate slightly to settle it. Measure the clearance between the edge of the choke plate and the throttle bore. Clearance should be 1.2-1.7mm (0.047-0.067 in.).
- If the clearance is incorrect, adjust by bending the choke lever.
Choke Unloader See Figure 23
- Close the choke plate fully. Open the throttle plate fully.
- Measure the clearance between the edge of the choke plate and the throttle bore with a wire gauge. Clearance should be 2.0-2.5mm (0.0787-0.9843 in.).
- If the clearance is incorrect, bend the choke unloader adjusting nail (tang).
Thermostat See Figure 24
- The index mark on the thermostat cover should be aligned with the center mark on the choke housing.
- Adjust by loosening the thermostat cover retaining screws slightly and shifting the position of the cover. Tighten the screws after adjustment.
Three choke related adjustments are performed on these units.
Choke Diaphragm See Figure 25
- Disconnect the vacuum line from the choke diaphragm unit.
- Using a vacuum pump, apply 15.7 in. Hg to the diaphragm.
- Using light finger pressure, close the choke valve. Check the clearance at the upper edge of the choke valve. Clearance should be 1.6-2.1mm (0.063-0.083 in.).
- If not, bend the tab on the choke lever to adjust it.
Choke Valve Clearance See Figure 26
- Position the fast idle lever on the second step of the fast idle cam.
- The leading edge of the choke valve should be 0.60-1.0mm (0.024-0.039 in.) from fully closed. If not, bend either the tab on the cam or the choke rod to adjust. The tab will give smaller adjustment increments.
Choke Unloader See Figures 27 through 33
- Open the primary throttle valve all the way and hold it in this position.
- The leading edge of the choke valve should be 2.74-3.60mm (0.1079-0.1417 in.) from fully closed. If not, bend the tab on the throttle lever.
REMOVAL & INSTALLATION
Label all vacuum and fuel lines to avoid confusion.
- Remove the air cleaner and duct.
- Disconnect the accelerator linkage from the throttle lever.
- Disconnect and plug the fuel supply and fuel return lines and plug these.
- Disconnect the leads from the throttle solenoid and deceleration valve at the quick-disconnects.
- Disconnect the carburetor-to-distributor vacuum line.
- Disconnect the throttle return spring.
- Disconnect the choke cable, and, if equipped, the cruise control cable.
- Remove the carburetor attaching nuts from the intake manifold studs and remove the carburetor. The attaching nuts are tucked underneath the carburetor body and are difficult to reach; a small socket with an "L" shaped hex drive, or a short, thin wrench sold for work on ignition systems will make removal easier.
- Install a new carburetor gasket on the manifold.
- Install the carburetor and tighten the carburetor attaching nuts.
- Connect the throttle return spring.
- Connect the accelerator shaft to the throttle shaft.
- Connect the electrical leads to the throttle solenoid and deceleration valve.
- Connect the distributor vacuum line.
- Connect the fuel supply and fuel return lines.
- Connect and adjust the choke cable and, if equipped, the cruise control cable.
- Install the air cleaner and duct.
- Start the engine and check for fuel leaks.
- Remove the air cleaner assembly, complete with its hoses and mounting bracket.
- Detach the choke and accelerator cables from the carburetor.
- Disconnect the fuel and vacuum lines from the carburetor.
- Remove the oil line which runs to the metering oil pump, at the carburetor.
- Unfasten the idle sensor switch wiring, if so equipped.
- Remove the carburetor attaching nuts and/or bolts, gasket or heat insulator, and remove the carburetor.
- Installation is performed in the reverse order of removal. Use a new gasket. Fill the float bowl with gasoline to aid in engine starting.
See Figures 34 through 39
The following instructions are general overhaul procedures. Most good carburetor rebuilding kits come replete with exploded views and specific instructions.
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 your carburetor in a clean, dust-free area. Carefully disassemble 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 parts in the solvent any longer than is necessary to sufficiently loosen the 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 airdry. Wipe clean all cork, plastic, leather, and fiber parts with a 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.
Check all parts for wear or damage. If wear or damage is found, replace the defective parts. Especially check 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.
Throttle shafts and bushings are not included in overhaul kits. They can be purchased separately.
- Inspect the idle mixture adjusting needles for burrs or 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 if necessary. If the valve is satisfactory, wash the valve again to remove breath moisture.
- Check the bowl cover for warped surfaces with a straightedge.
- Closely inspect the valves and seats for wear or 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 that deteriorate most rapidly. Failure to replace all parts supplied with the kit (especially gaskets) can result in poor performance later.
Some carburetor manufacturers supply overhaul kits of three basic types: minor repair; major repair; and gasket kits. Basically, they contain the following:Minor Repair Kits:
Major Repair 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 tight in their seats, but do not overtighten as the tips 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 lever when reassembling.