Pic. 9-15. Exhaust gas recirculation scheme: 1 - vacuum supply hose to the recirculation valve; 2 - hose for draining fluid from the carburetor heating unit; 3 - air filter; 4 - carburetor; 5 - air filter element; 6 - thermostat; 7 - engine; 8 - recirculation tube; 9 - recirculation valve; 10 - exhaust manifold; 11 - inlet pipe; 12 - thermal vacuum switch of the recirculation valve; 13 - carburetor heating block; A - to the vacuum ignition timing controller, B - to the coolant pump
When the engine coolant temperature is above 40-48°C, the thermal vacuum switch 12 is activated, a vacuum is applied to the recirculation valve 9, the valve opens, part of the exhaust gases from the exhaust manifold 10 is sucked into the intake pipe and the engine.
Checking the performance of the exhaust gas recirculation system
Press the carburetor throttle actuator lever and plan to increase the engine speed to 2500-3000 min-1. At a coolant temperature of 30-38°C, the recirculation valve 9 should be closed, and at a liquid temperature of 40-48°C, it should be open, as can be seen from the rise of the recirculation valve stem. If the recirculation valve does not open, check the valve and thermal vacuum switch 12.
To check, disconnect the recirculation valve 9 from the thermal vacuum switch 12 and apply vacuum using a manual vacuum pump to the diaphragm cavity of the valve. At a vacuum of 9.3 kPa (70±5 mm Hg) the valve must be closed At a vacuum of more than 59.9 kPa (450±5 mmHg Art.) the valve must be fully open, which is checked by a sharp removal of vacuum, the valve will close with a sharp click. Air leakage in both modes is not allowed within 5 s.
When checking the thermal vacuum switch 12, disconnect the hose from it and the recirculation valve 9. Use a manual vacuum pump to apply a vacuum of 13.3 kPa (100±5 mmHg Art.) to the thermal switch. At a coolant temperature of not more than 30-38°C, vacuum leakage is not allowed (thermal vacuum switch closed). At a liquid temperature of less than 40-48°C, vacuum should not be created (thermal vacuum switch open).