2010 Kawasaki KX250F Owners Manual - Page 143

142 TUNING TUNING Symptoms of Improper Mixture Carburetor Tuning a carburetor is not the mysterious science many racers believe it to be. One only needs to establish a basic knowledge of the identification and function of carburetor components as well as how they work together to do the job well. Temperature-and altitude-related mixture adjustment Condition* Mixture will be Adjustment Cold Air Warm Air Dry Air Low Altitude High Altitude (above 1 500 m or 4 900 ft) Leaner Richer Leaner Standard Richer Richer Leaner Richer None Leaner j If your machine exhibits one or several of the symptoms listed below, it may need carburetor tuning. Before attempting any changes, however, make sure that everything else is in good shape and properly tuned. Check the condition of the spark plug, make sure the ignition timing is correct, service the air cleaner element and decarbonize the muffler. If your machine has run properly on a certain track in the past and then starts running poorly with the same carburetor settings, the problem is almost certain to be elsewhere; changing the carburetor settings in such a case would probably be a waste of time. Symptoms when the mixture is too rich Poor acceleration Misfire at low engine speeds Excessive smoke Spark plug fouling A "deep" exhaust noise *: at constant atmospheric pressure and humidity The main jet size should be increased or decreased by one to five sizes and the engine tested until its power is maximum.