MOTORCRAFT Model 7200 VV 2-Barrel: Description

Systems on the Motorcraft model 7200 carburetor include: fuel inlet, main metering, control vacuum, cold enrichment, accelerator pump and choke system. The fuel inlet system has an integral filter at the inlet. Fuel level in fuel bowl is maintained by the float and lever assembly acting on the inlet valve and seat.

The main metering system provides fuel for normal engine operation. Vacuum created by air flowing through the venturi draws fuel from fuel bowl, up main well tubes, through main metering jets and into venturi.

Fuel flow is controlled by tapered metering rods linked to a venturi valve in the main metering jets. Small springs position the metering rods against top of main metering jet orifices for closer fuel flow control. A change in throttle plate position the metering rods to provide the correct fuel flow required by the amount of air flowing through the venturi.

The control vacuum system consists of the venturi valve diaphragm which is connected to the venturi valve. The diaphragm contains a spring to close the venturi valve and control vacuum with a calibrated spring to open the venturi valve. Vacuum source to the diaphragm comes from between the venturi valve and throttle plates.

As the throttle plates open, increased vacuum between the venturi valve and throttle plates causes the diaphragm to open venturi valve. The calibrated spring in the vacuum diaphragm maintains a precise air/fuel ratio for all engine operating conditions, except wide open throttle and choke operation.

During wide open throttle, vacuum is not strong enough to overcome the venturi valve diaphragm spring and open the venturi valve. A venturi valve limiter lever on the throttle shaft manually opens the venturi valve during wide open throttle.

The cold enrichment system provides a rich air/fuel mixture for cold engine operation. The extra fuel flow is metered by a tapered cold enrichment rod (CER) suspended from the upper body through a jet in the bottom of fuel bowl. The enrichment rod height is regulated by the choke bi-metal and choke control diaphragm position.

Enrichment fuel flows through an internal passage to the venturi discharge nozzles. A control vacuum regulator (CVR) restricts control vacuum to the venturi valve diaphragm. The CVR is also regulated by choke bi-metal and choke control diaphragm.

When the bi-metal is wrapped (closed), the CVR is lowered to raise the CER and provide more fuel. As the bi-metal unwraps (opens), the CVR rises to lower the enrichment rod to shut off fuel enrichment. The CER has adjustable cold operation positions.

Accelerator pump system is a positive displacement, pump type which provides additional fuel for sudden acceleration and full load operation. The choke system is a dual stage, electric choke cap and a choke control diaphragm.

The choke cap consists of a 2-stage ceramic heating disc and bi-metal spring. The first stage of the heating disc is always energized when engine is running to open choke plate a calibrated amount. The second stage is energized when engine compartment temperature is 54-75°F (12-24°C). The choke control diaphragm controls the cold enrichment system and fast idle cam.

The control diaphragm has an internal delay mechanism (2-5 seconds) which retracts the choke pulldown rod after engine start-up. The choke pulldown rod allows the fast idle cam to position the fast idle lever on the lower step.

The cold enrichment system is controlled in the following manner: the choke bi-metal positions the CER, CVR and fast idle cam based upon temperature. At 0°F (- 18°C), choke control diaphragm overrides bi-metal control operation when manifold vacuum is sensed. As bi-metal temperature increases, the bi-metal gradually takes over control of the system. Above 75°F (24°C), the diaphragm overrides the bi-metal to ensure good warm engine starts. To improve low temperature operation, cool air from the carburetor inlet flows inside the choke cap.

All 7200 model carburetors are equipped with external fuel bowl vent system. A hot idle compensator in the air horn improves hot engine idle quality. Depending on vehicle application, the carburetor may be equipped with an anti-dieseling solenoid, idle speed solenoid (A/C equipped), dashpot, vacuum kicker or any combination of these throttle positioners.

The 7200 carburetor is equipped with a feedback control actuator motor and throttle position sensor. These components are computer-controlled to provide precise metering of the air/fuel ratio, based upon input from various engine sensors.