1. GENERAL INFORMATION MXU 300/250 TROUBLESHOOTING ENGINE WILL NOT START OR IS HARD TO START Inspection/Adjustment Symptom Probable Cause Check if fuel reaches carburetor by loosening drain screw Empty fuel tank Clogged fuel line between fuel tank and carburetor Fuel does not Clogged float oil passage Fuel reaches Clogged fuel tank cap breather carburetor reach carburetor hole Clogged fuel filter Clogged fuel valve passage Remove spark plug and install it into spark plug cap to test spark by Faulty spark plug connecting it to engine Fouled spark plug ground Faulty ignition unit Faulty change gear control unit Spark jumps Weak or no spark Faulty pulser coil Broken or shorted ignition coil Broken or shorted exciter coil Faulty ignition switch Weak or dead battery Test cylinder compression Faulty starter clutch Valve clearance too small Valve stuck open Normal Low or no Worn cylinder, piston and piston compression compression rings Leaking cylinder head gasket Start engine by follow- ing normal starting procedure Air leaking through intake pipe Engine does not Engine fires but Leaking intake manifold fire does not start Incorrect ignition timing Incorrectly adjusted air screw Remove spark plug and inspect again Flooded carburetor Dry spark plug Wet spark plug Clogged air cleaner Throttle valve excessively open 1-26