Carburetor

GENERAL INFORMATION

Carburetor components on vehicles without a catalytic converter

1. Secondary chamber emulsion tube

2. Idle speed correction solenoid valve

3. Choke thermal actuator

4. Choke valve housing

5. Float chamber gasket

6. Accelerator pump lever

7. Bracket

8. Bracket

9. Secondary chamber venturi

10. Economizer jet

11. Idle mixture jet

12. Primary chamber main air jet

13. Primary chamber booster venturi

14. Economizer valve

15. Primary chamber main fuel jet

16. Body

17. Float chamber sight glass

18. Secondary chamber main fuel jet

19. Primary chamber idle jet

20. Needle valve

21. Float

22. Shaft

23. Accelerator pump piston

24. Primary chamber emulsion tube

25. Accelerator pump check valve

26. Accelerator pump valve

27. Fuel cut-off solenoid valve

28. Secondary chamber diaphragm

29. Accelerator pump coil

30. Gasket

31. Adjusting screw

32. Throttle damper

33. Body

34. Adjusting screw

35. Choke rod

36. Throttle lever

37. Accelerator pump rod

38. Mixture adjusting screw

39. Limiter sleeve

VEHICLES WITHOUT CATALYTIC CONVERTER. Nikki 21L carburetors are two-barrel, downdraft, with automatic choke. The secondary throttle valve is opened by a pneumatic actuator.

The carburetor body consists of three sections; the middle section is separated from the throttle valve section by a heat insulating spacer.

Idle speed is adjusted by a screw with a conical tip. Fuel cut-off is provided by a solenoid valve.

An economizer jet is provided for additional mixture enrichment at full engine load.

The mixture preparation system for normal engine operation includes the main fuel jet, emulsion tube, air jet and booster venturi.

An accelerator pump is provided for additional fuel injection during rapid acceleration; it is actuated by a rod connected to the throttle lever. Fuel dose of the accelerator pump depending on engine temperature is controlled by a solenoid valve operated by a thermal switch.

The idle speed adjusting screw is covered by a limiter sleeve.

Automatic increase of idle speed under additional engine load (for example when headlights or air conditioning are switched on) is provided by a bypass solenoid valve.

The choke valve is equipped with an electric thermal actuator, which is a spiral bimetallic spring heated by the flowing current.

VEHICLES WITH CATALYTIC CONVERTER. The carburetors of these vehicles are equipped with a fast-acting solenoid valve to maintain the stoichiometric air-fuel mixture, which is controlled by the control unit (this unit also controls ignition timing).

Signals from sensors are sent to the control unit.

The main control signals are from the air flow pressure sensor and the crankshaft angle sensor (the angle sensor is mounted in the ignition distributor).

Additional sensors whose signals are used to control the mixture composition are: – engine coolant temperature sensor; – throttle switch; – transmission neutral position switch; – clutch release switch; – vehicle speed sensor; – exhaust gas sensor.

The control unit compares incoming information and generates signals controlling ignition timing, mixture stabilization valve, idle speed, etc., ensuring optimal conditions for starting and operation of the engine at various temperature conditions.

To reduce exhaust emissions and maintain driveability of a cold engine, an electric heater is installed between the manifold and the carburetor. After the engine has warmed up, the control unit closes the cut-off valve, which improves fuel economy and reduces emissions into the atmosphere.

Some vehicles are equipped with exhaust gas recirculation and additional air intake systems.