- Mixture control solenoid travel should be checked before adjustment. Stop engine and remove air cleaner. Insert thin metal scale in "D" shaped hole in air horn. Press down to determine travel of solenoid. Total movement should be 1/8".
NOTE:
If solenoid movement is not correct, see appropriate Rochester Carburetor article in FUEL SYSTEMS Section for adjustment procedures.
- To adjust idle air bleed valve, set parking brake and block rear wheels. Disconnect and plug hoses as directed on Emission Control Decal in engine compartment. Check ignition timing and adjust if necessary.
- Connect dwell meter to lead wire from mixture control solenoid in carburetor, then set dwell meter to 6 cylinder scale. Start engine and run at idle until normal operating temperature is reached and a varying dwell is noted on dwell scale.
NOTE:
It is absolutely essential that engine is operated for sufficient length of time to ensure that engine coolant sensor, and oxygen sensor in exhaust, are at full operational temperature.
- Adjust curb idle speed, if necessary. With engine idling, observe dwell reading. If within, or varying between 10-50° range, no further adjustment is necessary. If dwell does not vary, or falls outside the 10-50° range, perform the following:
- With engine off, cover primary and secondary bore inlets with a shop towel or tape. Align a number 35 drill on the rivet head holding air bleed valve cover. Drill only enough to remove rivet head, then drive rivet out with small punch. Remove and discard air bleed valve cover.
- Restart engine and allow to idle, using a screwdriver that fully fits in valve. Slowly turn valve up or down until dwell reading varies and falls within the 25-35° range, attempting to be at or as close to 30° as possible.
CAUTION:
Perform this carefully. The idle air bleed valve is very sensitive in controlling air/fuel ratios and the valve should be turned only in 1/8 turn increments.
- If after performing this adjustment, the dwell reading does not vary and is not within the 25-35° range, it will be necessary to remove carburetor to gain access to plugs covering the idle mixture needles and adjust the idle mixture as follows:
- Turn mixture screws in until lightly seated, then back screws out the specified number of turns.
Preliminary Idle Mixture Screw Adjustment
| Application |
Turns Out |
| 4.3L (260") |
1 |
| 4.4L (267") |
1 |
| 5.0L (305") |
1 |
| 5.0L (307") |
1 |
| (1) - 3 turn preset, make final adjustment on vehicle. |
- Reinstall carburetor (without air cleaner and gasket). Start engine, run until fully warm, and repeat Idle Air Bleed Adjustment until dwell reading is varying and within specified limits.
- If unable to set to 25-35° dwell reading, turn mixture screws out 1 turn (if dwell is below 25°) or in 1 turn (if above 35°). Then reset idle air bleed valve to obtain correct dwell reading.
- If necessary, reset curb idle speed and fast idle speed to specifications. Disconnect dwell meter and tachometer. Unplug and reconnect vacuum hoses, reinstall air cleaner and gasket.