Start the engine and allow it to warm up to several minutes, so that the engine is at its normal operating temperature. Shut off the engine. Set the idle adjustment by turning the throttle stop screw (located at the top of the carburetor) in the clockwise direction until it makes contact with the throttle lever. Turn it 3 more full turns to completely open the throttle plate (component within the carburetor). A screwdriver may or may not be required, depending on the spring tension on the adjustment screw. Turn the pilot screw (located below the throttle stop screw) clockwise until it begins to become slightly tight, then back it out counterclockwise 1 and 1/2 full turns. Do not over tighten the pilot screw because carburetor damage will result. A screwdriver may or may not be required, depending on the spring tension on the adjustment screw. Start the engine again, and let it warm up for 2 minutes. Once the engine is at normal operating temperature again, slowly twist the throttle stop screw counterclockwise. Stop turning the screw when the engine idles at its normal rate of idle. This may be verified (if desired) with an rpm gauge. The normal rate of idle will be specified in the user manual for each lawn mower. Turn the pilot screw in both directions (clockwise and counter clockwise) to locate the best screw position to obtain the highest engine rpm (revolutions per minute). Repeat the adjustment of the throttle stop screw (step 4 above) and the pilot screw (step 5) until the pilot screw setting is found that produces the correct 'normal' idle speed. It may take several adjustments of each screw until this setting is found. Set the maximum speed adjustment on the carburetor by adjusting the set screw on the carburetor control lever (this lever is where the throttle control cable meets the carburetor linkage). Turn the set screw clockwise to decrease the maximum rpm attained, and counterclockwise to increase the maximum rpm attained. Close the throttle to idle speed. Slowly open the throttle to attain maximum engine speed. The maximum engine speed should not exceed manufacturer’s specifications. This may be verified (if desired) with an rpm gauge. The maximum rpm's allowed will be specified in the user manual for each lawn mower. Turn off the engine. The carburetor is now set. Be sure to check the operation of the engine while cutting grass (and the engine is under full load). Make any adjustments as necessary.