Tachometer (Lean Drop) Method

Warm engine to normal operating temperature. Place manual transmission in Neutral, automatic transmission in Drive ("2"). Turn on headlights and cooling fan.
Remove mixture screw limiter cap and turn screw counterclockwise (rich) until highest RPM is obtained. Adjust idle speed screw to obtain specified adjusting RPM (enriched RPM).
Now turn mixture screw clockwise (lean) until idle speed drops to idle RPM or RPM drop specified in applicable ENRICHED IDLE SPEED SPECIFICATIONS table. Replace limiter cap with point 180 degrees away from boss on carburetor body.

Fig 1: Accord & Prelude Idle Boost Diaphragm Adjustment
Courtesy of AMERICAN HONDA MOTOR CO., INC.

1974 ENRICHED IDLE SPEED SPECIFICATIONS

1975-76 ENRICHED IDLE SPEED SPECIFICATIONS

1977 ENRICHED IDLE SPEED SPECIFICATIONS

Application

Adjusting RPM

RPM Drop

Accord

Federal & Calif.

Man. Trans.

850

Auto. Trans.

710

High Alt.⁽¹⁾

Man. Trans.

920/970

120/170

Auto. Trans.

760/780

80/100

Civic

Man. Trans.

850

100

Auto. Trans.

800

Civic CVCC

Federal & Calif.

Man. Trans.

860

Auto. Trans.

740

High Alt.⁽¹⁾

Man. Trans.

920/970

120/170

Auto. Trans.

780/800

80/100

⁽¹⁾	First RPM reading (before slash) is at high altitude; second reading is at sea level.

1978 ENRICHED IDLE SPEED SPECIFICATIONS

1979 ENRICHED IDLE SPEED SPECIFICATIONS