Contents: Basic information ↡ Precautionary measures ↡
Basic information
On all carburetor models, the main parts of the fuel system are a Stromberg or Pierburg type carburetor, a gas tank, a mechanical fuel pump, metal and rubber supply and return fuel lines, an air cleaner and a cartridge type fuel filter (non-separable), fixed in the gas tank.
The gas tank is located in the front of the luggage compartment inside the vehicle.
The fuel pump supplies fuel from the fuel tank through the fuel filter. It flows through the fuel supply line to the carburetor float chamber, where the float and needle valve regulate the fuel level maintained in the chamber. Excess fuel is sent back to the fuel tank through the return fuel line.
Depending on the model, the air cleaner is located either on top of the camshaft cover or directly on top of the carburetor inlet. It contains replaceable paper and mesh filters. All models contain a thermostatic flap installed on the air cleaner. It allows outside air to be mixed with warm air from the exhaust manifold, which optimizes the temperature of the air entering the carburetor.
The type of carburetor installed on the car depends on the year of manufacture and the market of distribution of the car. Carburetors of the Stromberg CDT 175 or Pierburg 2E-E type can be installed.
On the Stromberg SOT 175 carburetor, the fuel supply when starting a cold engine and the increased idle speed are regulated by a temperature-delayed valve. It is a bimetallic plate that controls the supply of discharge to the diaphragm of the air damper starting device. When the cold engine starts, the valve cuts off the discharge supply to the diaphragm and the air damper is kept closed. As the bimetallic plate of the delay valve heats up when the current flows when the ignition is turned on, the discharge supply to the trigger diaphragm is gradually restored and the air flap opens. At the same time, the engine speed and the quality of the mixture return to the normal value. A fuel supply shut-off valve is also installed; it prevents the engine from running when the ignition is turned off and does not allow the engine speed to exceed a preset threshold.
For certain markets, the vehicles are equipped with electronically controlled Pierburg 2E-E carburetors. Idle speed (i.e.) and mixture quality are controlled by actuators of the throttle and air valves, respectively.
The engine operating parameters are monitored by a set of sensors and the entire system is controlled by an electronic control unit (ECU). At engine speeds above idle speed, the mixture quality is maintained by the choke actuator, which changes the position of the choke and, consequently, the amount of air entering the carburetor. At idle speed or near idle speed, the actuator controls the mixture by changing the position of the needle inside the idle speed correction air jet. This allows the mixture entering the engine through the idle speed correction jet to be either leaner or richer. Idle speed is monitored by the ECU and compared with data stored in the electronic memory of the unit. With the help of the ECU, idle speed is maintained at an optimal level under all engine operating conditions. The unit regulates the position of the throttle valve using the actuator. Feedback is implemented using the throttle valve potentiometer (position sensor). Secondary functions performed by actuators are engine braking when the shut-off valve is turned on, limiting the maximum engine speed and preventing the engine from running when the ignition is turned off.
Precautionary measures
Many of the operations described in this chapter involve disconnecting fuel lines, which may cause some fuel to leak. Before beginning work, carefully read the warnings stated above and the information handed out in the "Safety First!" section at the front of this book.
Warning: Gasoline is a very dangerous and volatile liquid, so no precautions are too much when working with it. Ventilate the premises well when working with gasoline - open windows and doors to create a draft. Do not smoke and do not allow open flames or uncovered lamps near the work area. Remember that household appliances such as heaters, kettles, hair dryers also pose a potential gasoline fire hazard. Always have fire extinguishers on hand and familiarize yourself with the rules for their use before starting work. Protect your eyes when working with the fuel system and immediately wash off gasoline that comes into contact with your skin with soap and plenty of water. Remember that gasoline vapors are just as dangerous as liquid gasoline; the canister from which gasoline is drained contains gasoline vapors and is potentially dangerous.
Caution: When working with fuel system components, pay special attention to cleanliness - dirt entering the fuel system can block the pipes, which will lead to interruptions in engine operation.