How to Adjust the Carburetor on a Lawn Boy

The Lawn-Boy name has long been synonymous with affordable and reliable mowers. If your Lawn-Boy has recently been serviced, or been in storage for a while, you may have to adjust the carburetor. A dead give-away that you need to adjust the carburetor on your Lawn-Boy is excessive gas consumption or black smoke when it's in operation. The process is the same for any model of Lawn-Boy, you just need to know where to locate the adjustment screws and how to adjust them to keep your Lawn-Boy mower running smoothly.

Things You'll Need

• Flat head screwdriver

Instructions

1. Locate the carburetor on your Lawn-Boy mower. Start at your gas tank and find the fuel line. Follow the fuel line to the carburetor. If your model is equipped with a fuel pump, continue following the line from the fuel pump to the carburetor. You'll know you have found it because unlike a fuel pump, the carburetor will look like a tube with a flat box on top with a circular attachment on the side, the pump looks like just a tube.

2. Locate and identify the three adjustment screws. If you can see two screws next to each other on the outside of the carburetor then the screw closer to the engine block is the idle air mixture screw; the one farthest from the block is the main air mixture screw. If there is only one screw on the side, this will be your idle screw and the main air screw will then be located toward the bottom of the carburetor. The third screw will be located either to the front or rear of your carburetor (depending on your model), this is the screw you use to set your engine idle.

3. Using a flat head screwdriver, slowly turn the idle air screw and the main air screw clockwise until they are "seated" in the carburetor. To "seat" a screw means to screw it in as far as it will go without tightening it into place, you want the head flush to the carburetor. Then, turn both screws counter-clockwise 1 1/2 turns.

4. Hold the throttle open on your Lawn-Boy mower (either using the throttle on the handle or removing the air filter and holding the plate in the center open so it is straight up and down).

5. Start the engine and turn the main air screw in small increments, either in or out (it will depend on your altitude and climate) until the engine runs smoothly and is not racing or stalling. Release the throttle.

6. Turn the engine idle screw slowly clockwise until the engine begins to sound as if it is going to stall. As soon as you hear this, turn the screw counter-clockwise (very slightly) until the mower runs smoothly. Give the engine gas and adjust the engine idle screw again so it is running smoothly when receiving gas.

Tips & Warnings

• The most common mistake people make in adjusting a carburetor is they do not turn the screws enough. Use a screwdriver with the name molded into the handle or place a mark on the handle, insert the head of the screwdriver into the screw making sure that the mark or label on the handle is facing up, turn the screwdriver until the label returns to the upright position to make one complete turn. A half turn will put the label facing down.

• Set the brakes on the wheels of your mower before adjusting the carburetor. When you give the mower gas and are still making adjustments, you do not want it to begin moving or you could become seriously injured.

References

• Small Engine Repair: Carburetor Adjustment

Resources

• How to Store Your Lawn Mower