Idle Speed & Mixture

NOTE: Mixture adjustment is NOT part of normal tune-up procedure and should not be performed unless carburetor is overhauled or vehicle fails emissions testing.

Switch off all accessories. Remove fuel filler cap. Disconnect and plug idle compensator tube at air cleaner. Connect tachometer to engine. Ensure parking brake is engaged and wheels are blocked.
On manual transmission models, make sure dashpot rod does not keep throttle lever from returning to stop. On air conditioned models, make sure throttle opener does not keep throttle lever from returning to stop.
Warm engine to normal operating temperature. Place automatic transmission in "D". Check idle speed. Adjust curb idle speed to specification by turning throttle adjusting screw.
NOTE: Idle mixture adjustment requires removal of carburetor to remove limiter cap.
Using a hacksaw, cut through limiter cap and mixture screw 0.4" (10 mm) from cap end. Remove mixture screw and install new mixture screw.
To install new mixture screw, tighten screw lightly and ensure it is fully seated. Back screw out 3 turns for preliminary adjustment. Reinstall carburetor with new gaskets and warm engine to normal operating temperature.
To adjust idle mixture, set idle speed to idle set specification by turning throttle set screw (automatic transmission in "N"). Set idle speed to highest RPM obtainable by turning mixture screw. Reset idle speed to idle set specification by turning throttle screw. See Figure .

Turn mixture screw until lean drop specification is obtained (automatic transmission in "N"). On automatic transmission, shift transmission to "D" and set idle speed to curb idle specification by turning throttle screw.

IDLE SPEED & MIXTURE

Application

Curb Idle RPM

Idle Set RPM

Lean Drop RPM

Man. Trans.

750

770

750

Auto. Trans.

⁽¹⁾ 750

⁽²⁾ 870

⁽²⁾ 840

⁽¹⁾	Transmission in "D".

⁽²⁾	Transmission in "N".

Fig 1: Carburetor Adjusting Screw Locations

Courtesy of MAZDA MOTORS CORP.