Check the air filter: A clogged air filter will enrich the air/fuel mixture, causing your four-wheeler to run rich. Clean or replace the air filter as needed.
Check the fuel adjustment screw: The fuel adjustment screw controls the amount of fuel flow into the carburetor. You will need a screwdriver to turn the screw. Turning the screw clockwise will lean out the mixture, while turning it counterclockwise will richen the mixture.
Adjust the idle speed screw: Increase the idle speed slightly. This will help the engine to pull more air into the carburetor, making the mixture leaner.
Test drive the four-wheeler: After making the adjustments, test drive the four-wheeler. Listen for any changes in how it runs. If you notice any hesitation, stumbling, or popping during acceleration, the mixture is too lean and you should turn the screw counterclockwise. If the four-wheeler runs rough or boggs down during acceleration, the mixture may be too rich.
Repeat as necessary: Repeat steps 2-4 until achieving the desired air/fuel mixture. Always err on the side of caution and make small adjustments each time.
