The carburetor used is a 2-barrel down-draft type with a low speed (primary) side and a high speed (secondary) side.
An electrically operated anti-dieseling solenoid is used on all engines. When the ignition switch is turned OFF, the valve is de-energized, shutting off the supply of fuel to the idle circuit.
All 1984 and later USA carbureted models are equipped with the ECC. System (Electronic Controlled Carburetor). The ECC control unit consists of a microcomputer, connectors for signal input and output and power supply, and an exhaust gas sensor monitor lamp. The control unit senses and controls various carburetor operations.
On all non-California models, the conventional choke valve and fast idle cam has been replaced with a duty-controlled solenoid valve for fuel enrichment and an idle speed control actuator (ISCA). These devices are controlled according to the engine speed, amount of intake air, and objective engine speed. Also, the air-fuel ratio and ignition timing are controlled according to the engine water temperature, atmospheric pressure, vehicle speed and transaxle gear position. In addition, this system controls the ignition timing and the idle speed according to applied electric loads such as a cooler, thereby achieving better emission control, fuel economy etc.
On California models the carburetor is equipped with an air-fuel ratio control on-off valve instead of a power valve. This on-off valve opens or closes the compensating air bleed and main jet to compensate for rich/lean air-fuel ratio, depending on varying conditions, such as acceleration, deceleration, low coolant temperature, low voltage, etc. These varying conditions are detected by various sensors which transmit corresponding signals to provide air-fuel ratio compensation.
- Disconnect the negative battery cable.
- Remove the air cleaner.
- Open the automatic choke valve by hand, while turning the throttle valve by pulling the throttle lever, then set the choke valve in the open position.
If equipped with a vacuum controlled throttle positioner, use a vacuum hand pump to retract the throttle positioner rod.
- Adjust the throttle cable at the carburetor bracket, so that 1.0-2.0mm of pedal free-play exists.
See Figures 1 and 2
A dashpot is used on carburetors of automatic transaxle equipped vehicles, as well as some manual transaxle models. The dashpot slowly closes the throttle on automatic transaxle equipped vehicles 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 2,300-2,500 rpm (E15) engines, 1,900-2,100 rpm (E16, automatic transaxle) or 2,250-2,450 (E16, manual transaxle).
Before attempting to adjust the dashpot, make sure the idle speed, timing and mixture adjustments are correct.
- Loosen the locknut (turn the dashpot, if necessary) and make sure the engine speed drops smoothly from 2,000 rpm to 1,000 rpm in 3 seconds.
- If the dashpot has been removed from the carburetor, it must be adjusted when installed. Adjust the gap between the primary throttle valve and the inner carburetor wall, when the dashpot stem comes in contact with the throttle arm. The dashpot gap is 0.66-0.86mm (manual transaxle) or 0.49-0.69mm (automatic transaxle).
See Figure 3
All carburetors discussed in this information 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 5.7-6.9mm between the throttle valve and the carburetor body. The easiest way to measure this is to use a drill bit. Drill bits from sizes H to P (standard letter size drill bits) should fit. if an adjustment is necessary, bend the connecting link between the two linkage assemblies.
The carburetor is equipped with a tang on the adjusting link, bend the tang to adjust the clearance.Float Level
See Figure 4
The fuel level is normal if it is within the lines or dot 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
See Figure 5
- Remove the carburetor from the vehicle.
On some California engines, disconnect the harness cover from the automatic choke heater cover, the vacuum hose from the vacuum break diaphragm (install a plug after pushing the vacuum break stem toward the diaphragm), then move the throttle lever counterclockwise (fully). Go to Step 4.
Remove the choke cover, then place the fast idle arm on the 2nd step of the fast idle cam. Using the correct wire gauge, 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:
1982-88 Sentra with manual transaxle-0.80-0.87mm
The first step of the fast idle adjustment procedure is not absolutely necessary.
- Install the carburetor on the engine.
- Start the engine, warm it to operating temperatures and check the fast idle rpm. The cam should be at the 2nd step.
1984-87 Sentra E16-
- 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.
See Figure 6
With the carburetor removed from the engine, turn the throttle arm until the adjusting plate comes in contact with the lock lever at point A and check clearance G . The clearance should be 0.25 in. (6.3mm).Choke Unloader
The choke must be cold for this adjustment. This adjustment does not apply to 1984 and later non-California USA models, nor to 1987 California/Canada models.
- 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.
The unloader cam is located next to the choke plate adjusting lever.
Adjustment is made by bending the unloader tongue. Gauge the gap between the choke plate and the carburetor body to:
See Figure 7
- With the engine cold, close the choke completely.
- Pull the vacuum break stem straight up as far as it will go.
- Check the clearance between the choke plate and the carburetor wall.
Clearance should be:
- Adjustment is made by bending the tang at the choke plate lever assembly.
Remove the choke cover, then connect a rubber band to the choke lever to hold it shut.Accelerator Pump
See Figure 8
If a smooth, constant stream of fuel is not injected into the carburetor bore when the throttle is opened, the accelerator pump needs adjusting.
- Remove the carburetor from the engine.
- Check the gap between the primary throttle valve and the inner wall of the carburetor when the pump lever comes in contact with the piston pin. This is the stroke limiter gap. It should be 1.3mm. If not, bend the stroke limiter.
- Fill the carburetor bowl with fuel.
- Fully open the choke.
- Place a calibrated container under the throttle bore. Slowly open and close the throttle (full open to full closed) ten times keeping the throttle open 3 seconds each time. Measure the amount of fuel in the container. The amount should be 0.3-0.5 ml. If not, and the stroke limiter gap is correct, replace the accelerator pump unit.
Check this valve if the engine continues to run after the key has been turned off.
- Run the engine at idle speed and disconnect the lead wire at the anti-dieseling solenoid. The engine should stop.
- If the engine does not stop, check the harness for current at the solenoid. If current is present, replace the solenoid. Installation torque for the solenoid is 13-16 ft. lbs. (18-22 Nm).
REMOVAL & INSTALLATION
- Remove the air cleaner.
- Disconnect the electrical connector(s), 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 torque the carburetor mounting nuts to 9-13 ft. lbs. (11-18 Nm).
- Install the throttle lever.
- Connect the electrical connector(s), the fuel and the vacuum hoses to the carburetor.
- Install the air cleaner.
- Start engine, warm engine and adjust as necessary.
See Figures 9, 10, 11, 12 and 13
Efficient carburetion depends greatly on careful cleaning and inspection during overhaul, since dirt, gum, water and/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 the 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, be sure that there are no restrictions or blockages. Never use wire or similar tools for cleaning purposes; clean the jets and valves separately, to avoid accidental interchange.
Check all the 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/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 level when reassembling.