PUMP ROD ADJUSTMENT

To check this adjustment, the primary throttle valves must be completely closed.

Back out idle stop screw on bowl away from stop tang on throttle lever. Disconnect end of secondary throttle valve actuating rod from primary throttle lever. Some models do not have an attaching clip so it will be necessary to bend the secondary throttle closing tang away from primary lever. The closing tang must then be readjusted after pump adjustment.

With throttle valves completely closed and pump rod in specified hole in pump lever, measure the distance from top of choke valve wall, next to vent stack, to top of pump stem with adjustable T-scale. Dimension should be as specified. Bend the pump lever as shown to adjust.

IDLE VENT VALVE ADJUSTMENT

After pump rod adjustment has been made, open the primary throttle to a point where the vent valve just closes.

With the adjustable T-scale, measure the distance from the top of the choke valve wall, next to vent stack, to stop of pump plunger stem. Bend the vent valve actuating wire until vent valve just closes at the dimension specified.

THERMOSTATIC TYPE

Some later models have a thermostatically operated idle vent valve. When adjusting this type valve, use the following procedure.

After the pump rod adjustment has been made, hold the vent valve closed and open the primary throttle to a point where the vent valve arm just contacts the bi-metal strip next to the rubber valve.

With adjustbale T-scale, measure the distance from the top of the choke valve wall next to vent stack to the top of pump plunger stem. Bend the vent valve actuating wire as shown to obtain specified setting dimension.

AIR VALVE ADJUSTMENT

(Early models only)

To check adjustment, hold air valve wide open against stop tang. Measure the distance between upper inside edge of air valve and the back side of choke valve wall on torsion spring side, as shown. Dimension should be as specified. Bend the top tang on dashpot lever as shown, to adjust.

FAST IDLE ADJUSTMENT

(This is a preliminary setting only, reset fast idle to correct RPM setting on car)

Place fast idle cam follower on highest step of fast idle cam. Back out fast idle screw until the primary throttle valves are completely closed and cam follower is away from highest step of cam. Then turn fast idle screw inward until the cam follower just contacts highest step of cam; from this point, turn screw two more complete turns. This presets the fast idle screw so that the following choke settings can be made accurately.

CHOKE ROD ADJUSTMENT

(Models 4MV and 4MC)

With the fast idle adjustment made, place the fast idle cam follower on the second step of the fast idle cam and against the rise to the highest step. Rotate the choke valve towards closed choke by pushing counter-clockwise on the vacuum break lever (model 4MV) or thermostatic coil tang in choke housing (model 4MC).

Measure the dimension with plug gauge between the lower edge of choke valve, at choke lever end and inside air horn wall.

To adjust, bend the choke rod at the point shown.

VACUUM BREAK ADJUSTMENT

4MV (Early models without air valve dashpot combination)

Some early models use a torsion spring to delay choke opening. On these units make sure tail of spring is located in top notch on choke bracket before adjustment.

To adjust the vacuum break, proceed as follows:

1. Place fast idle cam follower on highest step of fast idle cam.
2. Using vacuum source, connect to vacuum break diaphragm and set diaphragm.
3. Using light finger pressure, rotate vacuum break lever towards closed choke (Do not strech tension spring on Oldsmobile models as vacuum break link must stay in the end of slot away from diaphragm unit for proper adjustment). With the vacuum break lever held in this position, use specified plug gauge and insert between lower edge of choke valve and air horn wall (choke side).
4. To adjust to specified dimension, bend the vacuum break link at point shown. Use care to prevent distortion of vacuum break lever and fast idle cam pick-up pin. If small pick-up pin is bent, the choke bracket will have to be replaced.

VACUUM BREAK ADJUSTMENT

Model 4MC (Choke housing on bowl)

With choke cover and coil assembly and inside baffle plate removed, make the vacuum break adjustmnet as follows:

Step “A”

1. Place fast idle cam follower on highest step of fast idle cam.
2. Rotate choke coil lever inside choke housing until choke valve is completely closed.
3. Align choke coil pick-up tank on inside choke lever directly over index tab on inside of choke housing. If alignment is necessary, bend lever sideways at point shown.
4. After coil tang is aligned, adjust vacuum break tang to specified clearance between tang and vacuum break pin - choke valve held closed as in step 2. Bend vacuum break tang at point shown to obtain specified clearance.

Step “B”

1. Hold vacuum break diaphragm adjustment screw down against diaphragm cover and vacuum break tang on inside choke lever against diaphragm plunger pin.
2. Measure the distance between lower edge of choke valve and inside air horn wall (choke lever side) with plug gauge.
3. Make sure choke rod is in bottom of slot in choke shaft lever.