Contents: Float chamber ↡ Automatic starting system ↡ Idle system ↡ Main dosing system 1st stage ↡ Full load system ↡ 2nd stage transition system ↡ Accelerator pump ↡ Check valve ↡
Float chamber
The float chamber includes a float, a float shaft, a holder and a needle valve. The valve movement is limited by a wire bracket. Fuel from the fuel pump passes through the fuel filter and the open needle valve into the float chamber. When a certain fuel level is reached, the float rises and presses on the needle valve to stop the fuel flow. When the fuel level drops, the float drops and releases the needle valve, the valve rises until it stops against the bracket by fuel pressure and opens the fuel access to the float chamber. The float chamber is ventilated through the air filter in the carburetor cover. The carburetor has an internal ventilation system.
Automatic starting system
The starting automation is switched on automatically on a cold engine after pressing the fuel pedal once. The heating unit with a bimetallic plate is controlled by the coolant and the electric heater. The coolant heater is installed to prevent the starting automation from switching on again after a short-term engine shutdown. In addition to the starting automation, a TN-starter was installed during the production period of engines of this series (thermally controlled shunt starter). The composition of the working mixture during engine warm-up is regulated bypassing the throttle (shunt device), which speeds up engine warm-up. The step heater built into the starter cover heats the starting automation depending on the engine oil temperature and is controlled by a temperature switch, relay and additional resistance that regulates the voltage.
Idle system
The idle system is located in stage 1. Fuel is taken into the idle system behind the main jets. The vacuum that occurs when the throttle is closed sucks fuel from the float chamber into the fuel channel. Air, passing through the air jet, mixes with fuel, forming an emulsion that passes down through the open idle valves and outlet holes into the mixing chamber. The mixture composition is regulated by the idle adjusting screw, the screw movement is limited by a projection on the plastic cap. To ensure a smooth transition when turning on the main metering system of the 1st stage, the fuel-air mixture is additionally supplied through bypass holes. To quickly stop the engine after turning off the ignition, the windings of the idle electromagnetic valves are de-energized and the ball valves, under the action of springs, close the channels. The idle valves are positioned so that they block all channels for the passage of the mixture in the idle system.
Main dosing system 1st stage
Fuel from the float chamber enters the mixing chamber through the main jet. When the vacuum is high enough, fuel is sucked into the mixing chamber through the sprayer. When the rotation speed increases, the fuel level in the emulsion channel decreases and the holes of the emulsion tube open. Air passes through the air jets with a modified cross-section into the emulsion tube and, mixing with the fuel, forms an emulsion.
Full load system
The full load system is located in the 1st stage and changes the flow sections of the air jets using two calibrated needles controlled by the vacuum in the intake pipe. When the throttles are opened, the vacuum acting on the needle control piston decreases. The spring moves the piston upward and it lifts the calibrated needles, the ends of the larger diameter needles enter the jets. The annular gap between the holes of the jets and the needles decreases, the air flow through the gap decreases, which leads to enrichment of the fuel emulsion. There is an adjusting screw on the piston, the position of which is set at the manufacturer, during operation no additional adjustment of the screw is required.
2nd stage transition system
To ensure smooth activation of the main metering system of the 2nd stage, a transition system drilling is located directly under the air damper. When the air damper is opened, under the action of vacuum, fuel is sucked into the reserve chamber through the transition system drilling. Through a calibrated hole, fuel flows from the float chamber into the reserve chamber and is sucked in through the pressure tube. The mixture is formed directly in the gap of the slightly open throttle.
Damping of the 2nd stage air damper The damper is controlled by a vacuum and is designed to prevent the sudden opening of the air damper. The damper body is connected by drilling to a vacuum, which counteracts the vacuum in the air damper area. The drilling position of the transition system and the dimensions of the diaphragm are selected in such a way that the vacuum acting on the air damper tends to open it.
Accelerator pump
The accelerator pump is of the diaphragm type. Fuel is injected through a calibrated hole or jet in the carburetor cover.
Fuel is sucked into the pump chamber through the inlet valve from the float chamber. The pump chamber is covered with a layer of heat-insulating plastic. When steam locks occur, they are led out into the float chamber through the ventilation hole. When the diaphragm is pressed, fuel is injected into the mixing chamber through the discharge valves and the calibrated hole. Two discharge valves prevent air from entering the pump chamber when fuel is sucked in.
Check valve
The check valve is controlled by the vacuum in the intake pipe. At idle speeds and partial load modes, the diaphragm moves downwards under the vacuum, overcoming the force of the springs, and opens the valve, the fuel in the return pipe is drained into the fuel tank. In acceleration and full load modes, the vacuum decreases, the diaphragm moves in the opposite direction and the valve closes the drain channel.