Carburetor Zenith 1B3 (VW Golf 2)

1. Adjusting the engine speed on the suction side:

a) Remove the air filter assembly.

b) Connect a speed meter to the engine.

c) Turn the intake speed cam 1 so that the adjusting bolt 2 is on the highest tooth of the cam (figure 3.19).



d) Start the engine without pressing the gas pedal and record the suction speed.

d) If the suction speed does not correspond to the technical data, remove the safety cap and adjust the speed by turning the adjusting bolt 2 (figure 3.19).

2. The position of the adjusting screws is shown in Figure 3.20A and 3.20B.





3. Adjusting the starting diaphragm gap.



a) Remove the water chamber cover and the bimetallic spring assembly of the starting equipment. There is no need to disconnect the electrical wire and elastic water pipes from the cover assembly,

b) Rotating the throttle, set the intake speed cam 1 so that the adjusting bolt 2 is on the highest tooth (figure 3.19).

c) Pressing the adjusting screw 1 of the diaphragm gap with a screwdriver, move the diaphragm control lever towards the low pressure servomotor unit to the stop (figure 3.21).



d) In this position of the lever, check the gap between the edge of the diaphragm and the wall of the carburetor neck using a drill with a diameter of 4.3 mm.

d) If necessary, adjust the gap by turning screw 1.

e) After completing the adjustment, install the starter equipment cover. The marking on the cover must match the corresponding marking on the starter equipment body.

4. Launch equipment servomotor unit.

The operation of the low pressure servomotor unit can be checked as follows:

a) With the air filter assembly removed, start the engine at idle speed.

b) Manually close the start diaphragm and observe the operation of the servomotor. If the diaphragm can be easily closed to a gap of approximately 4 mm, and then a certain resistance is felt, then the servomotor is working correctly. If the diaphragm can be completely closed without any resistance, this indicates damage to the diaphragm of the servomotor or a leak in the low-pressure system.


c) If the diaphragm is ruptured or torn, it must be replaced.

d) If the diaphragm is normal, it is necessary to check the reduced pressure at the entrance to the servomotor.

5. Pre-heater in the drive manifold:

6. There is a pre-heater in the drive manifold. It serves to pre-heat the fuel-air mixture flowing through the manifold. This is done to facilitate the evaporation of fuel at low temperatures. Its operation can be checked as follows:

a) Disconnect the preheater assembly electrical wire from the connection near the carburetor. This is the wire that goes to the drive manifold below.

b) Check the resistance between the end of the pre-heater wire and ground. It should be 0.25-0.50 Ohm. If the resistance is different, the pre-heater unit must be replaced with a new one (figure 3.22).



6. Thermal switch:

Two thermal switches screwed into the engine cooling system control the current supply to the automatic suction heater unit and the pre-heater in the drive manifold depending on the coolant temperature. The red one controls the automatic suction, and the transparent one controls the pre-heater in the manifold.

The operation of the thermal switches can be checked using a test light (figure 3.22)

a) Before removing the switch on a cold engine, disconnect the wiring connections and connect a test lamp in series between the end of the electrical wire supplying the thermal switch and the end of the thermal switch. With the ignition on, the test lamp should light. If the lamp does not light, the switch is faulty and must be replaced. If the lamp lights, remove the switch and hang it in a container of water. The test lamp should be connected to the positive terminal of the battery and the end of the thermal switch, and the negative terminal of the battery to the body of the thermal switch. Heat the water, the lamp should go out when the temperature is between 30-40°C (red switch) or between 50-55°C (transparent switch), otherwise the corresponding switch must be replaced.