Idle Mixture Adjustment

WITH ROCHESTER E2SE CARBURETOR
The E2SE carburetor is used with electronic fuel control systems which control air/fuel mixture during all ranges of engine operation. Because of this system control, special preliminary checks and adjustment procedures are required. Procedures must be followed exactly, in sequence, to insure correct mixture adjustment.

The dwell reading from the Mixture Control (MC) solenoid is used as an adjustment calibration. While it is normal for dwell readings to fluctuate over a 5 degree range, temporary mixture variations may cause dwell readings to fluctuate as much as 10 to 15 degrees. Dwell readings specified for adjustment are the average of the most consistant variation.

Pre-set Procedure
1. Remove plug covering idle mixture adjusting screw as outlined in "Concealment Plug Removal" procedure in the Carburetor Section. Turn metal screw in (clockwise) until lightly seated, then back screw out 5 turns.

Fig. 5 Rochester ES2E carburetor mixture control adjustments (typical):

2. If idle air bleed valve plug, Fig 5, has been removed, turn air bleed valve screw in (clockwise) until lightly seated, then back screw out 3 turns. If plug is in place, do not adjust idle air bleed valve screw in (clockwise) until lightly seated, then back screw out 3 turns. If plug is in place, do not adjust idle air bleed valve screw.
3. Remove vent stack screen to gain access to lean-mixture screw in bottom of float bowl, Fig. 5.
4. Turn lean mixture screw in (clockwise) until lightly seated, then back screw out 2 1/2 turns.
5. Install carburetor on engine with air cleaner off and related vacuum fittings plugged.
6. Disconnect bowl vent hose at carburetor. Disconnect and plug vacuum hoses at EGR valve and T fitting in bowl vent hose. Disconnect canister purge hose at carburetor and plug vacuum fitting.
7. Remove secondary vacuum break thermal vacuum switch from air cleaner, then disconnect hose to thermostatic air cleaner from switch, and plug fitting on switch. Leave all other vacuum hoses connected to switch.
8. Connect dwell meter to test lead (green wire) in MC solenoid harness and set meter on 6 cylinder scale. Connect tachometer to engine following manufacturer's instructions.
9. Start engine and run at fast idle until engine cooling fan cycles and engine enters "closed loop" mode of operation, indicated by a fluctuating dwell reading.

Mixture Adjusting Procedure
Perform adjustments with automatic transmission in neutral, unless otherwise noted.

1. Run engine at 3,000 RPM and adjust lean mixture screw, as needed to obtain a dwell reading of 35 degrees. If reading is too low, turn screw counterclockwise; if reading is too high, turn screw clockwise.

NOTE: Make adjustments in small increments, allowing time between adjustments for engine and dwell meter to stabilize.

2. Return engine to idle and adjust idle speed to 700 RPM with engine cooling fan off.
3. Adjust idle mixture screw, as needed, to obtain a dwell reading of 25 degrees, with engine cooling fan off. If reading is too low, turn screw counterclockwise; if reading is too high, turn screw clockwise.

NOTE: Make adjustments in small increments, allowing time between adjustments for engine and dwell meter to stabilize. Make final check with mixture adjustment tool removed.

4. With engine cooling fan off, disconnect wiring harness connector to MC solenoid. Engine speed should change at least 50 RPM. If not check for restriction, leak, etc., in idle air bleed circuit.
5. Run engine at 3,000 RPM while observing dwell meter. Meter should indicate fluctuating dwell with an average reading of 35 degrees. If reading is not within specifications, repeat steps 1-5.
6. Reinstall vent screen stack, reconnect vacuum hoses to proper fittings, and reinstall air cleaner. Check and adjust curb idle speed to specifications, as needed.