Accelerator Pump and Bowl Vent
- Back off the idle speed screw and open the choke valve so that when the throttle valves are closed the fast idle adjustment screw does not contact the fast idle cam.
- Be sure that the pump operating rod is in the medium stroke hole (long hole for the BBS-4340S and BBS-4341S) in the throttle lever and that the bowl vent clip on the pump stem is in the center notch (lower notch on the BBS-4340S and BBS-4341S).
- Close the throttle valves tightly. It should just be possible to insert a 1 / 16 " drill bit between the bowl vent and the air horn ( 27 / 32 " on the BBS-3277S pump plunger travel).
- If an adjustment is necessary, bend the pump operating rod at the lower angle.
Fast Idle Cam PositionAUTOMATIC CHOKE ONLY
- Adjust the fast idle speed as described later.
- Place the fast idle screw on the second highest step of the fast idle cam.
- Move the choke valve towards the closed position with light pressure on the choke shaft lever.
- Insert a #48 drill bit between the choke valve and the wall of the air horn. If an adjustment is necessary, bend the fast idle rod at the upper angle.
- If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
- If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 10 in.Hg (15 in.Hg for 1976 and later models).
- Insert a #35 drill bit between the choke valve and the wall of the air horn.
- Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
- Remove the drill bit. If a slight drag is not felt as the drill bit is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
- Refit the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
- With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
The choke unloader adjustment is a mechanical device that partially opens the choke valve at wide open throttle. It should be adjusted as follows:
- Hold the throttle valve in the wide open position.
- Insert a 3 / 16 " drill bit between the upper edge of the choke valve and the wall of the air horn.
- With a finger pressing lightly against the choke plate, a slight drag should be felt as the drill is being withdrawn.
- If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
Fast Idle Speed
- Warm the engine by driving at least five miles.
- With the engine off and the transmission in Park or Neutral, open the throttle slightly.
- On models without the Clean Air Package, close the choke plate about 20°, then allow the throttle plates to close. The fast idle screw should now rest on the slowest speed step of the cam.
On models with the Clean Air Package, close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
- Start the engine.
- Turn the fast idle speed screw in or out until the specified speed is obtained.
- Stopping the engine between adjustments is not necessary. However, be sure to position the fast idle speed screw on the cam after each speed adjustment.
Spring Staged Choke
- Push on the choke hub lever with your finger, at the closed position. A small opening should exist between the shaft and hub levers.
- Using a drill bit, measure the opening. The opening should be 0.010-0.040".
- If not, bend the hub lever tang until the correct opening is reached.
- With the idle speed and mixture properly set and a tachometer installed, position the throttle lever so that the actuating tab on the lever contacts the stem of the dashpot but does not depress it.
- The engine speed should be 1,00 rpm. To adjust the setting, if necessary, loosen the locknut and screw the dashpot in or out as required. When the correct setting has been obtained, tighten the locknut against the bracket.
This procedure can be performed without removing the carburetor from the engine.
- Remove the accelerator pump operating rod.
- Remove 2 of the long air horn screws and 2 of the short screws. Install the 2 short screws in place of the 2 long screws. This will hold the main body to the throttle body. Tighten the screws securely.
- Remove the remaining air horn screws.
- Tilt the air horn far enough to disengage the fast idle cam link from the fast idle cam. Remove the air horn and gasket.
- Seat the float fulcrum pin by pressing on the fulcrum pin retainer. There should be enough fuel in the bowl to raise the float so that the lip bears firmly against the needle. Additional fuel may be entered by slightly depressing the float. If there is not enough pressure in the line to enter more fuel, you'll have to add some from a clean container.
- With the fuel level holding the tip of the float against the inlet needle, check the gap between the gasket surface of the bowl (gasket removed) and the center crown of the floats. The gap should be 1 / 4 " on BBS models 4177S, 4342S and 4341S; 7 / 32 " on models 4340S and 3277S.
- If adjustment is necessary, hold the float on the bottom of the bowl and bend the float tip toward or away from the needle as required. Recheck the gap.
Do not allow the float lip to depress the needle, as this will give you a false reading. When correctly set, the float lip should be perpendicular to the needle+-10°.
- Assemble the air horn.
- Check the idle speed.