mxu 400 Manuel atelier : Page 34

                    Troubleshooting

Problem: Engine will not start or is hard to start (Compression too low)
Condition                                               Remedy
 1.   Valve clearance out of adjustment                 1.   Adjust clearance
 2.   Valve guides worn                                 2.   Replace cylinder head
 3.   Valves mistimed                                   3.   Adjust valve timing
 4.   Piston rings worn excessively                     4.   Replace rings
 5.   Cylinder bore worn                                5.   Replace - rebore cylinder
 6.   Spark plug seating poorly                         6.   Tighten plug
 7.   Starter motor cranks too slowly - does not turn   7.   Check - replace starter motor
Problem: Engine will not start or is hard to start (No spark)
Condition                                               Remedy
 1.   Spark plug fouled                                 1.   Clean - replace plug
 2.   Spark plug wet                                    2.   Clean - dry plug
 3.   Magneto defective                                 3.   Replace magneto
 4.   CDI unit defective                                4.   Replace CDI unit
 5.   Ignition coil defective                           5.   Replace ignition coil
 6.   High-tension lead open - shorted                  6.   Replace high tension lead
Problem: Engine will not start or is hard to start (No fuel reaching the carburetor/fuel injector)
Condition                                               Remedy
 1.   Gas tank vent hose obstructed                     1.   Clean vent hose
 2.   Carburetor float valve defective                  2.   Replace valve
 3.   Fuel hose obstructed                              3.   Clean - replace hose
 4.   Fuel screens obstructed                           4.   Clean - replace inlet screen - valve screen
 5.   Fuel pump defective                               5.   Replace fuel pump
Problem: Engine stalls easily
Condition                                               Remedy
 1.   Spark plug fouled                                 1.   Clean plug
 2.   Magneto defective                                 2.   Replace magneto
 3.   CDI unit defective                                3.   Replace CDI unit
 4.   Carburetor jets obstructed                        4.   Clean jets
 5.   Valve clearance out of adjustment                 5.   Adjust clearance
Problem: Engine noisy (Excessive valve chatter)
Condition                                               Remedy
 1.   Valve clearance too large                         1.   Adjust clearance
 2.   Valve spring(s) weak - broken                     2.   Replace spring(s)
 3.   Rocker arm - rocker arm shaft worn                3.   Replace arm - shaft
 4.   Camshaft worn                                     4.   Replace camshaft
 5.   Valve tappets worn                                5.   Replace tappets
Problem: Engine noisy (Noise seems to come from piston)
Condition                                               Remedy
 1.   Piston - cylinder worn                            1.   Replace - service piston - cylinder
 2.   Combustion chamber carbon buildup                 2.   Clean chamber
 3.   Piston pin bore worn                              3.   Replace piston
 4.   Piston pin worn                                   4.   Replace piston pin
 5.   Piston rings - ring groove(s) worn                5.   Replace rings - piston



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