Stromberg PS Carburetor The PS series carburetor is a low-pressure, single-barrel,  injection-type carburetor. The carburetor consists basically  of the air section, the fuel section, and the discharge nozzle  mounted together to form a complete fuel metering system.  This carburetor is similar to the pressure-injection carburetor;  therefore, its operating principles are the same. In this type carburetor, metering is accomplished on a mass  airflow basis.  [Figure 2-28]  Air flowing through the main  venturi creates suction at the throat of the venturi, which  is transmitted to the B chamber in the main regulating part  of the carburetor and to the vent side of the fuel discharge  nozzle diaphragm. The incoming air pressure is transmitted  to a chamber A of the regulating part of the carburetor and  to the main discharge bleed in the main fuel discharge jet.  The discharge nozzle consists of a spring-loaded diaphragm  connected to the discharge nozzle valve, which controls the  flow of fuel injected into the main discharge jet. Here, it is  mixed with air to accomplish distribution and atomization  into the airstream entering the engine. In the PS series carburetor, as in the pressure-injection  carburetor, the regulator spring has a fixed tension, which  tends to  hold the poppet valve open during idling speeds  or until the D chamber pressure equals approximately 4  psi. The discharge nozzle spring has a variable adjustment  which,  when tailored to maintain 4 psi, results in a balanced  pressure condition of 4 psi in chamber C of the discharge  nozzle assembly and 4 psi in chamber D. This produces a  zero drop across the main jets at zero fuel flow. At a given airflow, if the suction created by the venturi is  equivalent to  1 ⁄ 4 pound, the pressure decrease is transmitted  to chamber B and to the vent side of the discharge nozzle.  Since the area of the air diaphragm between chambers A  and B is twice as great as that between chambers B and D,  the  1 ⁄ 4 pound decrease in pressure in chamber B moves the  diaphragm assembly to the right to open the poppet valve.  Meanwhile, the decreased pressure on the vent side of the  discharge nozzle assembly causes a lowering of the total  pressure from 4 pounds to 3 3 ⁄ 4 pounds. The greater pressure  of the metered fuel (4 1 ⁄ 4 pounds) results in a differential across  Figure 2-28.  Schematic of the PS series carburetor. Throttle valve Venturi Discharge air bleed Impact air (chamber A) Unmetered fuel Metered fuel  Inlet fuel pressure  Venturi suction (chamber B)  Pressure above throttle Intake air Vapor vent Poppet valve Fuel pressure connection Idle cutoff cam Manual mixture control needle valve Fuel inlet Idle cutoff plunger Impact air Venturi suction Fuel strainer Venturi drain Discharge nozzle Discharge nozzle needle valve Main metering jet Accelerating pump suction channel Accelerating pump Relief valve Manual idle control rod Idle needle valve Vacuum channel reducer A B D C 2-20