Magneto is an important electrical equipment of motorcycle. Magneto consists of magneto rotor and stator winding. The stator winding consists of a charging winding which provides the working power to the ignition system and a power winding which provides the working power to the charging system. With the increase of time spent on motorcycle and the influence of many factors, the magnetism of magneto rotor will gradually weaken. When the magneto rotor loses its excitation seriously, it will affect the normal operation of charging winding and power winding, and reduce the effective value of AC output voltage of charging winding and power winding, thus affecting the point. The normal operation of fire system and charging system.
        First of all, it is difficult to start the engine, which is caused by the weakening of the high-pressure ignition spark generated by the ignition system when the engine is starting. Next, the battery will also suffer from power shortage, which is caused by the reduction of the output power of the charging system.


Under normal conditions, the difficulty of starting motorcycle is easy to attract the attention of drivers and maintenance personnel. Maintenance personnel will first consider the failure of ignition system, and then go to check and inspect. Very few of them will inspect whether the magneto rotor has a loss of excitation fault. Besides, in the absence of special equipment, there is no good method to check and confirm whether there is a loss of excitation fault in the rotor of the magneto. In most cases, a screwdriver is used to touch the magnet of the magneto rotor, and the suction of the magnet is felt by hand to judge whether the magneto rotor has a loss of excitation fault. Because there is no definite comparative reference to do comparative test, the accuracy of the test judgment is low.


When the high-voltage ignition spark weakens in the ignition system, which leads to the difficulty of starting the engine, it should be first analyzed and judged whether the charging winding fault is caused by the charging winding fault or the loss of excitation fault of the magneto rotor. We can judge from the fact that the RMS of AC output voltage of charging winding and power winding will decrease significantly after the loss of excitation of the magneto rotor.


Disconnect the connection between the connecting wire of charging winding and the cable harness connector. The multimeter uses AC voltage pad to test the AC voltage output of charging winding. Use foot start or electric start, so that the engine into start-up conditions, write down the reading of the multimeter.


If the valid value of AC output voltage of charging winding is lower than the normal value after testing, the valid value of AC output voltage of power winding should be detected, the connection between connecting wire of power winding and cable harness connector should be disconnected, and the multimeter should use AC voltage gear to validate the valid value of AC output voltage of power winding. Check and record the reading of the multimeter.
If the effective value of the AC output voltage of the power winding is lower than the normal value, it can be determined that there is a loss of excitation fault in the rotor of the magneto. The rotor of the magneto should be magnetized or the rotor of the magneto should be replaced.

If the valid value of AC output voltage of power winding is normal after testing, then it can be concluded that the technical status of the magneto rotor is good, indicating that the charging winding is indeed faulty, which leads to the weakening of high voltage ignition spark, and a new charging winding should be replaced.
The advantage of this method is that through detection and inspection, the suspect points of the fault can be determined as soon as possible and the fault can be eliminated quickly. If the valid value of AC output voltage of charging winding is obviously reduced after testing, the replacement of charging winding is compared and checked. The fault of high-voltage ignition spark weakening can not be eliminated, and then the magnetic motor rotor is checked for loss of excitation, which increases the operation time.


If the magneto rotor is first inspected for loss of excitation, the magneto rotor can be replaced for comparative inspection when the loss of excitation fault of the magneto rotor is confirmed. When confirming that there is no loss of excitation fault in the rotor of the magneto, the doubtful point of the fault can be locked in the charging winding, and then troubleshooting can be done with half the effort. In fact, there is an easier way to solve the difficult start-up fault caused by loss of excitation, that is, to replace the DC igniter directly, but there is no good way to charge it weakly.