SECONDARY AIR VALVE SETTING (PRE 1970)

A pre-determined load on the air valve plates is necessary to prevent them from fluttering under changing load conditions. Should they be allowed to flutter, the engine would develop an unwanted surge.

The following adjusting procedure is suggested:

1. Loosen the air valve spring housing retainer.
   1. Let the housing rotate to a no-load position.
2. Hold the air valve plates in the closed position.
   1. Note the plastic housing position in relation to the index line of the casting.
   2. Rotate the housing counterclockwise 135* (six knobs).
3. Tighten the housing retainer.

ACCELERATOR PUMP STROKE AND FUEL BOWL VENT VALVE ADJUSTMENTS

It often becomes necessary to alter the accelerator pump stroke adjustment to meet requirements for different ambient conditions. The pump stroke on this carburetor has been calibrated to inject a predetermined quantity of fuel into the air stream with the pump pivot pin in the center (#2) hole. The amount may be altered by inserting the pivot pin in:

The LEFT (#1) hole to decrease the fuel quantity

The RIGHT (#3) hole to increase the fuel quantity.

The following adjusting procedure is suggested:

1. Remove the pump rod-to-pump arm retainer. Remove the rod from the arm.
2. Remove the pump pivot pin retainer. Remove the pivot pin.
3. Insert the pivot pin into the desired hole. The holes in the fuel bowl vent lever, main body casting and the pump lever must be in line.
4. Install the pivot pin retainer. Position the pump rod end into the pump arm and install the retainer.

The fuel bowl vent valve is adjusted to a specified clearance to support carburetor calibration. The adjustment can be made with the carburetor on or off the engine. If adjustment is necessary, refer to the preceding illustration, and follow the following suggested procedure:

1. Set the throttle plates in the closed position.

2. Check the clearance between the vent valve and the valve seat on the air horn casting

3. To achieve the specified clearance, bend the end of the vent valve lever:

   Downward to decrease the clearance

   Upward to increase the clearance

NOTE: Beginning with 1970 production, the vent valve has been eliminated on all Ford Motor Company vehicles, except the Thunderbird, Lincoln-Continental and Continental Mark III.

IDLE SPEED AND MIXTURE ADJUSTMENTS

A preliminary idle adjustment can be made with the carburetor on or off the engine.

Turn the idle mixture adjusting screw clockwise (inward) until they lightly seat.

Turn the mixture adjusting screws counter-clockwise (outward) 1 1/2 turns.

NOTE: Final adjustments are made on the vehicle after engine temperatures are normalized. Then, install an engine tachometer and measure the engine curb idle speed. Adjust to specification as follows.

Turn the idle air bypass screw clockwise (inward) to decrease the idle rpm, and counter-clockwise (outward) to increase idle rpm.

Turn the idle mixture screw clockwise (inward) until the rpm begins to drop, then, turn the screw counter-clockwise (outward) 1/4 turn.

Repeat the above step for the second idle mixture screw.

Touch-up (slightly rotate in either direction) idle mixture screws for smoothest idle quality. The screws should be withing 1/8 turn of each other. It may be necessary to readjust the idle air bypass screw to maintain specified idle rpm.

To adjust the idle air bypass screw (Pre-1970) the following procedure is suggested:

1. Turn the idle air bypass screw clockwise (inward) until it lightly seats.
2. Turn the screw counter-clockwise (outward) 3 1/2 turns.

NOTE: Beginning with 1970 production, the idle air bypass is no longer used.

On carburetors in which the idle air bypass screw has been eliminated, a throttle stop screw has been added. This is the method by which the throttle plate is “cracked” open to establish the idle rpm, and a method employed by carburetor manufacturers for many years.

Also note in the above illustration, that the idle mixture screws use a plastic idle limiter. This limiter permits only about a 3/4” turn on the mixture adjusting screws. As ou will recall, this reduces the possibility of an improper air-fuel ratio adjustment by unqualified personnel.