How to Adjust the Air-Fuel Mixture in a Carburetor?
2 Answers
Taking the carburetor plunger as the central line, if the mixture screw is on the side of the carburetor's fuel-air outlet, it adjusts the fuel type—turning clockwise leans the mixture, while counterclockwise enriches it. If the mixture screw is on the side where air enters the carburetor from the air filter, it adjusts the air type—turning clockwise enriches the mixture, while counterclockwise leans it. This is the most convenient and effective method. After adjusting the air-fuel mixture, it is essential to ride at low to medium speeds for 7-10 KM. You can then check the spark plug color to determine if the adjustment is appropriate.
Adjusting the carburetor mixture ratio is key to keeping the engine running smoothly. I often do this myself because older cars are prone to this issue. Start the engine and let it warm up to normal operating temperature, keeping it idling. At this point, locate the mixture screw—usually the small spring-loaded screw at the bottom of the carburetor. Slowly turn it counterclockwise or clockwise: counterclockwise leans the mixture (more air), while clockwise enriches it (more fuel). Listen to the engine sound while adjusting—if the RPM stabilizes without sputtering, it's correct. Setting it too rich wastes fuel and produces black smoke, while setting it too lean causes power loss or even overheating damage. A basic screwdriver tool is recommended. Adjustments may also be needed seasonally, especially at high altitudes where thin air can cause over-rich conditions. Regularly check spark plug color for feedback: white indicates lean, black indicates rich, and a medium brown is perfect.
