1. GENERAL INFORMATION MXU 300/250 POOR PERFORMANCE (ESPECIALLY AT IDLE AND LOW SPEEDS) Inspection/Adjustment Symptom Probable Cause Check ignition timing Faulty ignition unit Correct timing Incorrect timing Faulty pulser coil Check carburetor air screw adjustment Mixture too rich (turn screw Correctly adjusted Incorrectly adjusted out) Mixture too lean (turn screw in) Check carburetor gasket for air leaks Deteriorated O-ring Carburetor not securely No air leak Air leaks tightened Damaged insulator rubber Remove spark plug and install it into spark plug cap to test spark by connecting it to engine ground Faulty or fouled spark plug Faulty ignition unit Weak or inter- Faulty A.C. generator Good spark mittent spark Faulty ignition coil Broken or shorted spark plug wire Faulty ignition switch 1-28