Features of the device
Single-chamber with falling flow and variable diffuser cross-section, has a main metering system, an idle system, a diaphragm accelerator pump, an automatic starting device (since July 1983 a starting device with a manual drive on engines of all models except LPA) and an electromagnetic shut-off valve of the idle system (Fig. 2.77).
Fig. 2.77. Ford carburetor parts.
1 - throttle shaft; 2 - mixture quality screw; 3 - bypass channel adjustment screw; 4 - float; 5 - needle valve; 6 — fuel jet of the main metering system; 7 - air damper; 8 - dosing needle; 9 - Automatic starting device; 10 - bimetallic spring; 11 — control diaphragm of the valve; 12 — accelerator pump diaphragm.
The carburetor has a float chamber and a diffuser, the flow section of which depends on the vacuum above the pneumatic drive diaphragm. The vacuum in front of the throttle valve created by the engine determines the opening value of the diffuser valve. Depending on the established section of the diffuser, the metering needle regulates the flow section of the main fuel jet. The diffuser valve and the metering needle have a kinematic connection with each other. The flow section of the main fuel jet and the conical sections of the metering needle are manufactured with high precision. They are a matched pair and are not disassembled during operation.
Operating principle of the main dosing system
The main metering system includes the main fuel jet, the compensating jet and the conical needle. Fuel comes from the carburetor float chamber to the main fuel jet and through the annular section between the walls of the jet and the needle enters the diffuser. The air flow rate remains constant, providing the necessary atomization of gasoline in all engine operating modes. Improved fuel atomization ensures stable engine operation on a lean mixture while maintaining engine power and reducing the CO content in the exhaust gases. At low engine speeds, the metering needle, connected to the valve, almost completely closes the main fuel jet.
As the engine load increases, the vacuum in the diffuser and above the pneumatic drive diaphragm also increases, which increases the opening of the valve. The valve acts on the metering needle located in the main fuel and compensation jets. Moving the metering needle increases the opening of the main fuel jet, i.e. more fuel enters the engine. The metering needle is made in such a way and with such precision that under any engine load, a strictly defined amount of fuel enters it. Changing the shape of the needle is not allowed.
In idle mode, when the engine consumes small volumes of air, the valve is held in its original position by the return spring of the diaphragm, the throttle valve of the carburetor is closed. The control vacuum has a small value.
When the throttle valve opens, the vacuum increases, which acts on the diaphragm of the pneumatic drive (vacuum regulator), which, by compressing the return spring, opens the valve until equilibrium is established between the force of the return spring and the control vacuum.
Fig. 2.78. Operating principle of a carburetor with a variable diffuser cross-section.
1 - float; 2 - float chamber; 3 - bypass channel; 4 - dosing needle; 5 - main and auxiliary jets; 6 - air valve; 7 — throttle valve. The arrow indicates the air inlet.
Fig. 2.79. Fuel supply by the accelerator pump.
1 - diaphragm spring; 2 - diaphragm; 3 - discharge valve; 4 - inlet valve; 5 - removal of gasoline vapors; 6 - throttle valve; I — Air; II - Gasoline; III - Fuel-air mixture; IV - Fuel supply; V — Vacuum supply channel.
The article was taken in its entirety from the specified website Fordbook.ru