Since the design of the 2700VV (variable venturi) carburetor differs considerably from the other carburetors in the Ford lineup, an explanation of the theory and operation is presented here.
In exterior appearance, the variable venturi carburetor is similar to a conventional carburetor and, like a conventional carburetor, it uses a normal float and fuel bowl system. However, the similarity ends there. In place of the normal choke plate and fixed area venturis, the 2700VV carburetor has a pair of small oblong castings in the top of the upper carburetor body where you would normally expect to see the choke plate. These castings slide back and forth across the top of the carburetor in response to fuel-air demands. Their movement is controlled by a spring-loaded diaphragm valve regulated by a vacuum signal taken below the venturis in the throttle bores. As the throttle is opened, the strength of the vacuum signal increases, opening the venturis and allowing more air to enter the carburetor.
Fuel is admitted into the venturi area by means of tapered metering rods that fit into the main jets. These rods are attached to the venturis, and, as the venturis open or close in response to air demand, the fuel needed to maintain the proper mixture increases or decreases as the metering rods slide in the jets. In comparison to a conventional carburetor with fixed venturis and a variable air supply, this system provides much more precise control of the fuel-air supply during all modes of operation. Because of the variable venturi principle, there are fewer fuel metering systems and fuel passages. The only auxiliary fuel metering systems required are an idle trim, accelerator pump (similar to a conventional carburetor), starting enrichment, and cold running enrichment.
Adjustment, assembly and disassembly of this carburetor require special tools for some of the operations. These tools are available (see the Tools and Equipment Section). Do not attempt any operations on this carburetor without first checking to see if you need the special tools for that particular operation. The adjustment and repair procedures given here mention when and if you will need the special tools.
The Motorcraft model 7200 variable venturi (VV) carburetor shares most of its design features with the model 2700VV. The major difference between the two is that the 7200VV is designed to work with Ford's EEC (electronic engine control) feedback system. The feedback system precisely controls the air/fuel ratio by varying signals to the feedback control monitor located on the carburetor, which opens or closes the metering valve in response. This expands or reduces the amount of control vacuum above the fuel bowl, leaning or enriching the mixture accordingly.Fast Idle Speed
See Figure 1
- Remove the air cleaner assembly, if necessary.
- Place the transmission in Neutral or Park and connect a suitable tachometer.
- Start the engine and bring it to normal operating temperature.
- Disconnect and plug the EGR vacuum line.
- Place the fast idle lever on the specified step of the fast idle cam. (Refer to the engine compartment sticker or the Carburetor Specifications chart for the proper setting.) If so equipped, make sure that the high speed cam positioner lever is disengaged.
- Turn the fast idle speed screw clockwise to increase or counterclockwise to decrease the fast idle speed.
- Rev the engine momentarily, place the fast idle lever on the specified step and recheck the fast idle rpm.
- Shut off the ignition. Disconnect and remove the tachometer.
- Remove the plug from the EGR vacuum line and connect the line.
- Install the air cleaner assembly, if no further adjustments are required at this time.
See Figure 2
You will need a special choke adjustment tool for this job: Ford calls it a stator cap (#T77L-9848-A or equivalent). It fits over the choke thermostatic lever when the choke cap is removed.
- Remove the choke coil cap. On 1980 and later California models, the choke cap is riveted in place. The top rivets will have to be drilled out. The bottom rivet will have to be driven out from the rear. New rivets must be used upon installation.
- Place the fast idle lever in the corner of the specified step of the fast idle cam, counting the highest step as first. (Refer to the engine compartment sticker or the Carburetor Specifications chart for the proper setting.) Be sure that the high speed cam positioner, if so equipped, is retracted.
- If the adjustment is being made with the carburetor removed, hold the throttle lightly closed with a rubber band to maintain cam position.
- Turn the stator cap clockwise until the lever contacts the fast idle cam adjusting screw.
- Turn the fast idle cam adjusting screw until the index mark on the cap lines up with the specified mark on the choke casting.
- Remove the stator cap and install the choke coil cap. Set it to the specified casting mark.
See Figure 3
- Place the high cam speed positioner in the corner of the specified cam step, counting the highest step as the first.
- Place the fast idle lever in the corner of the positioner.
- Hold the throttle firmly closed.
- Remove the diaphragm cover. Adjust the diaphragm assembly clockwise until it lightly bottoms. Turn it counterclockwise 1 / 2 -1 1 / 2 turns until the vacuum port and diaphragm hole line up.
- Replace the diaphragm cover.
See Figure 4
- Remove the carburetor from the engine.
- Remove the upper body assembly and the upper body gasket.
- Invert the upper body and measure the vertical distance between the cast surface of the upper body and the bottom of the float. (The normal range is 1.015-1.065 inches.)
- To adjust, bend the float operating lever away from the fuel inlet needle valve to decrease the setting, or toward the needle valve to increase the setting. Make sure that the float remains parallel to the gasket surface.
- Check the float drop and adjust, if necessary, as described below.
- Install a new upper body gasket and reinstall the upper body assembly.
See Figure 5
- Remove the carburetor upper body assembly and upper body gasket.
- Hold the upper body assembly upright and measure the vertical distance between the cast surface of the upper body and the bottom of the float. (The normal range is 1.435-1.485 inches.)
- To adjust, bend the stop tab on the float lever away from the hinge pin to increase the setting, or toward the hinge pin to decrease the setting.
- Install a new upper body gasket and reinstall the upper body assembly.
A dial indicator and stator cap (Ford part #T77L-9848-A or equivalent) are required for this adjustment.
- Remove the choke coil cap. See Step 1 of the Fast idle Cam Adjustment.
- Attach a weight to the choke coil mechanism to seat the cold enrichment rod.
- Install and zero-set a dial indicator with the tip of the top of the enrichment rod. Raise and release the weight to verify zero on the dial indicator.
- With the stator cap at the index position, the dial indicator should read the specified dimension. Turn the adjusting nut to correct it.
- Install the choke cap at the correct setting.
- Make sure the idle speed is correct.
- Using a 5 / 16 in. Allen wrench, turn the venturi valve diaphragm adjusting screw clockwise until the valve is firmly closed.
- Connect a vacuum gauge to the vacuum tap on the venturi valve cover.
- Idle the engine and use a 1 / 8 in. Allen wrench to turn the venturi bypass adjusting screw to the specified vacuum setting. You may have to correct the idle speed.
- Turn the venturi valve diaphragm adjusting screw counterclockwise until the vacuum drops to the specified setting. You will have to work the throttle to get the vacuum to drop.
- Reset the idle speed.
This adjustment is necessary only on non-feedback (2700VV) systems.
- Remove the carburetor. Remove the venturi valve diaphragm plug with a center-punch.
- If the carburetor has a venturi valve bypass, remove it by removing the two cover retaining screws; invert and remove the bypass screw plug from the cover with a drift. Install the cover.
- Install the carburetor. Start the engine and allow it to reach normal operating temperature. Connect a vacuum gauge to the venturi valve cover. Set the idle speed to 500 rpm with the transmission in Drive.
- Push and hold the venturi valve closed. Adjust the bypass screw to obtain a reading of 8 in. Hg on the vacuum gauge. Make sure the idle speed remains constant. Open and close the throttle and check the idle speed.
- With the engine idling, adjust the venturi valve diaphragm screw to obtain a reading of 6 in. Hg. Set the curb idle to specification. Install new venturi valve bypass and diaphragm plugs.
Venturi Valve Limiter
See Figure 6
- Remove the carburetor. Take off the venturi valve cover and the two rollers.
- Use a center punch to loosen the expansion plug at the rear of the carburetor main body on the throttle side. Remove it.
- Use an Allen wrench to remove the venturi valve wide open stop screw.
- Hold the throttle wide open.
- Apply a light closing pressure on the venturi valve and check the gap between the valve and the air horn wall. To adjust, move the venturi valve to the wide open position and insert an Allen wrench into the stop screw hole. Turn clockwise to increase the gap. Remove the wrench and check the gap again.
- Replace the wide open stop screw and turn it clockwise until it contact the valve.
- Push the venturi valve wide open and check the gap. Turn the stop screw to bring the gap to specifications.
- Reassemble the carburetor with a new expansion plug.
The cold enrichment metering rod adjustment must be checked and set before making this adjustment.
- After adjusting the cold enrichment metering rod, leave the dial indicator in place but remove the stator cap. Do not re-zero the dial indicator.
- Press down on the C.V.R. rod until it bottoms on its seat. Measure this amount of travel with the dial indicator.
- If the adjustment is incorrect, hold the 3 / 8 in. C.V.R. adjusting nut with a box wrench to prevent it from turning. Use a 3 / 16 in. Allen wrench to turn the C.V.R. rod; turning counterclockwise will increase the travel, and vice-versa.
REMOVAL & INSTALLATION
On vehicles with an automatic transmission, the transmission kickdown lever or the throttle valve lever must be adjusted whenever the carburetor assembly is removed for service or replacement.
- Remove the air cleaner assembly.
- Disconnect the throttle cable from the throttle lever.
- Disconnect the vacuum lines, emission hoses, fuel line and electrical connection.
- On EEC-equipped vehicles, disconnect the throttle position sensor connector at the loom.
- Remove the carburetor retaining nuts. Lift off the carburetor carefully, taking care not to spill any fuel. Remove the carburetor mounting gasket and discard it. Remove the carburetor mounting spacer, if so equipped, from the intake manifold.
- Prior to installation, clean the gasket mounting surfaces of the intake manifold, spacer (if so equipped), and carburetor. When using a spacer, use two new gaskets, sandwiching the spacer between the gaskets. If a spacer is not used, only one new carburetor mounting gasket is required.
- Install the spark and EGR port vacuum lines, if so equipped, before bolting the carburetor in place.
- On EEC-equipped vehicles, connect the throttle position sensor plug, and secure the wire loom.
- Place the new gasket(s) and spacer (if so equipped) on the carburetor mounting studs. Position the carburetor on top of the gasket and hand tighten the retaining nuts. Then tighten the nuts in a crisscross pattern to 12-15 ft. lbs.
- Connect the fuel line, throttle cable, and all vacuum lines and emission hoses which were removed.
- Install the air cleaner assembly.
- Check and adjust the engine idle speed settings, as outlined in Engine Electrical .
The 2700VV and 7200VV carburetors are part of the extremely sophisticated EEC system. Although various adjustments have been covered, it is recommended that these units not be overhauled.