A: First off, make sure the correct size, (cfm) carburetor is installed on the engine and be sure the idle mixture screws are properly adjusted (see page 6 of the Owner's Manual). You can always make your carburetor leaner, but this will not always improve gas mileage. Since every engine is different, there is no way of knowing how much of an affect leaning down the carburetor will have on your engine. You can refer to your carburetor owners manual (download here) and the calibration chart inside to lean down the carb. Start off light, but keep an eye on the plugs to make sure you aren’t taking it too lean. You will see on the chart that you can lean the carburetor down in different percentages in different modes, cruise and power.