How to Adjust the Air-Fuel Mixture When the Motorcycle Spark Plug Turns Black?
2 Answers
Motorcycle spark plug turns black method to adjust the air-fuel mixture: First, gently turn the mixture screw clockwise all the way in, then turn it counterclockwise one and a half turns; this should be approximately the correct mixture position. For more precise adjustment, first adjust the idle speed to around 1000 RPM, then finely adjust the mixture screw left and right. During adjustment, the idle speed will increase or decrease. Adjust it to the point where the idle speed is the highest. Then, lower the idle speed back to what you consider appropriate. At this point, if you turn the mixture screw either clockwise or counterclockwise, the RPM should decrease. This indicates the optimal air-fuel mixture has been achieved.
Blackened spark plugs are usually a sign of a rich air-fuel mixture, something I've learned well from years of tinkering with old bikes. A rich mixture could be due to a clogged air filter or a misadjusted carburetor. Start by cleaning the air filter, then check the mixture screw on the carburetor—typically, turning it clockwise leans out the mixture, but don’t overdo it. Adjust it a quarter turn at a time, then restart and test-ride for a few kilometers to check. Before testing, always remove and clean the spark plug; the color changing from black to brown means you’ve got it right. I remember when I was younger, reckless adjustments made the spark plugs even blacker, hurting acceleration and causing stalling, so take it slow. Finally, check if the engine temperature is normal, as overheating can also interfere. Safety first—find an open space and take your time.
