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How to Set the Carb on a Cub Cadet Tractor

Tip

Some Cub Cadet carburetors may have a limiter cap installed on the low idle fuel adjustment screw to regulate its adjustment to within certain parameters. The screw cannot be turned beyond the limits of the cap.

Cub Cadet is an American company that manufactures power lawn and garden equipment, such as string trimmers, walk-behind lawnmowers and riding garden tractors. The Cub Cadet garden tractor has a four-stroke gasoline engine mounted up front to power the rear wheels and various attachments, such as a cutting deck. The fuel delivery system on the engine is a carburetor which ensures the engine has the correct fuel-to-air mixture. Adjustments can be performed on the carburetor to fine-tune the fuel-to-air mixture.

Start the engine and set the throttle lever to the halfway mark. Let the engine run approximately 10 minutes to bring it to operating temperature. Move the throttle lever to its lowest setting and allow the engine to idle.

  • Cub Cadet is an American company that manufactures power lawn and garden equipment, such as string trimmers, walk-behind lawnmowers and riding garden tractors.
  • Move the throttle lever to its lowest setting and allow the engine to idle.

Open the hood. Locate the carburetor mounted on the side of the engine behind the air cleaner assembly. Locate the low idle fuel adjustment screw near the bottom of the carburetor where it attaches to the intake manifold.

Turn the low idle fuel adjustment screw counterclockwise using a flat-head screwdriver until the engine speed starts to decrease, indicating the fuel-to-air mixture is rich. Make a mental note of the position of the screw.

Turn the low idle fuel adjustment screw clockwise until the engine speed increases. Continue to turn the screw clockwise until the engine speed decreases again, this time indicating the fuel-to-air mixture is lean. Make a mental note of the position of the screw.

  • Locate the carburetor mounted on the side of the engine behind the air cleaner assembly.
  • Turn the low idle fuel adjustment screw counterclockwise using a flat-head screwdriver until the engine speed starts to decrease, indicating the fuel-to-air mixture is rich.

Turn the low idle fuel adjustment screw to a point midway between the too-rich and too-lean settings established previously in the procedure.

Connect a portable auto tester to the engine using the instructions that came with the tester. Switch the tester to the tachometer function. Make sure the tester indicates that the idle speed is between 1200 and 1500 rpm, depending on the model of tractor. Check the owner’s guide for your particular model to find the exact idle speed required.

Turn the idle speed adjustment screw on top of the carburetor with a flat-head screwdriver in the direction needed until the tester shows the correct engine rpm. Disconnect the tachometer, shut off the engine and close the hood.

  • Turn the low idle fuel adjustment screw to a point midway between the too-rich and too-lean settings established previously in the procedure.
  • Turn the idle speed adjustment screw on top of the carburetor with a flat-head screwdriver in the direction needed until the tester shows the correct engine rpm.

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