Toro lawn mower, tractor and snow thrower models all utilize Briggs & Stratton 4-cycle engines as standard equipment. The carburetors on these machines have all been adjusted at the factory, but an occasional adjustment must be made depending on the operating environment and the number of elapsed hours since the last tune-up was performed. Adjusting a Toro (Briggs & Stratton) carburetor is a simple procedure most homeowners can master by following a few simple steps.
Prep the Mower and Familiarize Yourself With Its Adjustment Screws
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To begin, park the mower on a flat and level surface and be sure it has adequate gas in the tank. Start the engine and allow it to warm up for at least five minutes.
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Find the three main adjustments screws on the Briggs & Stratton engine: power adjusting screw (on the bottom of the carburetor facing vertically), idle mixture screw (in the middle of the carburetor facing horizontally) and the idler speed screw (near the top of the carburetor facing horizontally).
Adjust the Screws With Engine Off
Turn off the engine. Close the power adjusting screw (on the bottom of the carburetor facing vertically) by gently turning it clockwise with your fingers until you feel some seating resistance.
Open the power adjusting screw by turning it counterclockwise one full turn (360 degrees) with your fingers. Close the idle mixture screw (in the middle of the carburetor facing horizontally) by gently turning it clockwise with your fingers until you feel some seating resistance.
Open the idle mixture screw by 1 1/2 turns (540 degrees) by gently turning it counterclockwise with your fingers.
Adjust the Screws With Engine On
Start the engine again (it should still be warm). Wait one minute, then turn the throttle to the fast (or full) position. Rotate the power adjusting screw clockwise 1/8 of a turn at a time, until the engine begins to run roughly (mixture is too lean).
Next, rotate the same power adjusting screw counterclockwise 1/8 of a turn at a time until the engine begins to run roughly again (mixture too rich). Then turn the power adjusting screw clockwise again to the midpoint between the too lean and too rich screw positions so the engine runs smoothly again.
Reduce throttle to normal idle speed. Rotate the idler speed screw clockwise until the engine idles fast.
Rotate the idle mixture screw clockwise 1/8 of a turn at a time, until the engine begins to run roughly (mixture is too lean). Next, rotate the same idle mixture screw counterclockwise 1/8 of a turn at a time, until the engine begins to run roughly again (mixture too rich). Then turn the idle mixture screw clockwise again to the midpoint between the too lean and too rich screw positions so the engine runs smoothly again.
Finally, rotate the idler speed screw until the engine idles normally.
Note that the actual settings for the power adjusting screw and the idle mixture screw depend on many variables, so it may take several attempts to set the carburetor correctly.