The carburetor used is a 2-barrel downdraft type with a low speed (primary) side and a high speed (secondary) side.
All models have an electrically operated anti-dieseling solenoid. As the ignition switch is turned off, the valve is energized and shuts off the supply of fuel to the idle circuit of the carburetor.
On all models, make sure the throttle is wide open when the accelerator pedal is floored. Some models have an adjustable accelerator pedal stop to prevent strain on the linkage.Dashpot
A dashpot is used on carburetor of all cars with automatic transmissions and many late model manual transmission models. The dashpot slowly closes the throttle on automatic transmissions to prevent stalling and serves as an emission control device on all late model vehicles.
The dashpot should be adjusted to contact the throttle lever on deceleration at approximately 1,900-2,100 rpm for automatic transmissions or 1,600-1,800 rpm for automatic transmissions with the L-series engines. The Z20S engine's dashpot contact point should be between 1,400-1,600 rpm for automatic transmissions.
Before attempting to adjust the dashpot, make sure the idle speed, timing and mixture adjustments are correct.Secondary Throttle Linkage
All Datsun/Nissan carburetors discussed in this guide are two stage type carburetors. On this type of carburetor, the engine runs on the primary barrel most of the time, with the secondary barrel being used for acceleration purposes. When the throttle valve on the primary side opens to an angle of approximately 50° from its fully closed position, the secondary throttle valve is pulled open by the connecting linkage. The 50° angle of throttle valve opening works out to a clearance measurement of somewhere between 6.5-8.0mm between the throttle valve and the carburetor body. The easiest way to measure this is to use a drill bit. Drill bits from size H to size P (standard letter size drill bits) should fit. If an adjustment is necessary, bend the connecting link between the two linkage assemblies.Float Level
The fuel level is normal if it is within the lines on the window glass of the float chamber (or the sight glass) when the vehicle is resting on level ground and the engine is off.
If the fuel level is outside the lines, remove the float housing cover. Have an absorbent cloth under the cover to catch the fuel from the fuel bowl. Adjust the float level by bending the needle seat on the float.
The needle valve should have an effective stroke of about 1.5mm. When necessary, the needle valve stroke can be adjusted by bending the float stopper.
Be careful not to bend the needle valve rod when installing the float and baffle plate, if removed.Fast Idle
- With the carburetor removed from the vehicle, place the upper side of the fast idle screw on the second step (first step for 1977-81 L and Z engines) of the fast idle cam and measure the clearance between the throttle valve and the wall of the throttle valve chamber at the center of the throttle valve. Check it against the following specifications:
1973-74 610, 1974 710:
1975-76 610, 710:
1977 710, 1978-79 510, 200SX:
The first step of the fast idle adjustment procedure is not absolutely necessary.
- Install the carburetor on the engine.
- Start the engine and measure the fast idle rpm with the engine at operating temperature. The cam should be at the 2nd step.
1974-76 710, 610:
1977 710, 1978-79 510, 200SX:
- To adjust the fast idle speed, turn the fast idle adjusting screw counterclockwise to increase the fast idle speed and clockwise to decrease the fast idle speed.
- With the engine cold, make sure the choke is fully closed (press the gas pedal all the way to the floor and release).
- Check the choke linkage for binding. The choke plate should be easily opened and closed with your finger. If the choke sticks or binds, it can usually be freed with a liberal application of a carburetor cleaner made for the purpose. If not, the carburetor will have to be disassembled for repairs.
- The choke is correctly adjusted when the index mark on the choke housing (notch) aligns with the center mark on the carburetor body. If the setting is incorrect, loosen the three screws clamping the choke body in place and rotate the choke cover left or right until the marks align. Tighten the screws carefully to avoid cracking the housing.
- Close the choke valve completely.
- Hold the choke valve closed by stretching a rubber band between the choke piston lever and a stationary part of the carburetor.
- Open the throttle lever fully.
- Adjust the gap between the choke plate and the carburetor body to:
L-series engines, 1980-81 Z20S engine:
Exc. 710: 2.4mm
REMOVAL & INSTALLATION
- Remove the air cleaner.
- Disconnect the electrical connector(s) if so equipped, the fuel and the vacuum hoses from the carburetor.
- Remove the throttle lever.
- Remove the four nuts and washers retaining the carburetor to the manifold.
- Lift the carburetor from the manifold.
- Remove and discard the gasket used between the carburetor and the manifold.
- Install carburetor on the manifold, use a new base gasket and tighten the carburetor mounting nuts to 9-13 ft. lbs.
- Install the throttle lever.
- Connect the electrical connector(s) if so equipped, the fuel and the vacuum hoses to the carburetor.
- Install the air cleaner.
- Start engine, warm engine and adjust as necessary.
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 to allow them to air dry. 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 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 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 level when reassembling.