a) Connect a speed meter to the engine.
b) Open the throttle, close the diaphragm completely, then release the throttle. The suction speed adjusting screw should be on the uppermost tooth of the suction speed cam (figure 3.23).
Figure 3.23. Zehith 2B5 carburetor
1 - adjusting screw; 2 cam.
c) Without pressing the gas pedal, start the engine and record the value of the rotation speed at the suction.
[The original can be seen on the portal www.vwmanual.ru]
d) This speed should be 3600 rpm. If it is different, it must be adjusted by removing the safety plug and turning the adjusting screw 1.
2. The position of the adjusting screws is shown in Figure 3.24.
Figure 3.24A. Carburetor - 2B5
1 - exhaust gas composition adjusting bolt.
Figure 3.24B. Carburetor - 2B5
2 - idle speed adjusting bolt.
a) Remove the water chamber cover and the bimetallic spring assembly of the starting equipment. It is not necessary to disconnect the heater wire and the elastic water pipes from the cover assembly.
b) Rotate the throttle to set the speed cam on the intake so that the limiting bolt is on the highest tooth of the cam. Use a screwdriver to press the diaphragm rod 1 to its limiter. Use rubber band 2 to support the diaphragm control lever pressed to its limiter.
3 a) Remove the water chamber cover and the bimetallic spring assembly of the starting equipment. It is not necessary to disconnect the heater electrical cable and the elastic water pipes from the cover assembly.
b) Rotate the throttle to set the intake speed cam so that the limiting bolt is on the highest tooth of the cam. Use a screwdriver to press the diaphragm rod 1 to its limiter (figure 3.25). Use rubber band 2 to support the diaphragm control lever, pressed against its stop
Figure 3.25. Zenith 2B5 carburetor
1 - diaphragm thrust, 2 - compression rubber.
c) Press the diaphragm lightly. Tilting and closing the diaphragm eliminates any gaps in the mechanism connections. Then check the gap between the lower edge of the diaphragm and the wall of the neck with a diameter of 3.7 mm.
d) If necessary to adjust this gap, turn the adjusting screw at the end of the diaphragm rod.
d) After completing the adjustment, install the starter equipment cover. The sign on the cover must match the corresponding sign on the starter equipment body.
4. Second pass carburetor thrust:
The second-pass throttle is controlled by the discharged air through a low-pressure servomotor, which is connected to the throttle lever by a short rod. In the 2B5 carburetor, this unit is made of artificial material and is not adjustable.
5. Fuel level:
To check the fuel level, it is necessary to remove the top cover of the carburetor. Since this requires disconnecting the connecting rod of the starting diaphragm, it is recommended to check the clearance of the starting diaphragm after installing the top cover of the carburetor to ensure that the cover is correctly positioned. Unscrew the top cover of the carburetor, as shown in Figure 3.26, it is impossible to measure the distance from the top of the float to the plane (without gasket). During the measurement, the float must not be pressed with the measuring instrument. Dimension a is shown in Figure 3.26.
Size A: for the first pass - 28 mm, for the second pass - 30 mm.
This check is best done using a template with a corresponding cutout made of hard cardboard or similar material. If adjustment is necessary, the float arms can be bent. To do this, the float must be removed.
6. Thermal switch:
On the 2B5 carburetor, the thermal switch unit, similar to that installed on the 1VZ carburetor, controls the current supply to the automatic intake heater unit and the drive manifold preheater. It is necessary to check the thermal switches, their required values, measured during the check, as well as for the 1VZ carburetor.
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