In my lifetime, I have seen many flywheels with damaged magnets and loose magnets, but I only replaced one flywheel for weak magnets. It was a Yamaha Timberwolf. Just so happens, the engine ran, but the lights didn't work - the owner wanted the lights to work - how hard can it be to get lights to work? When I checked the wiring diagram, I found that the lights worked on AC right off the alternator. The unit had two alternator windings - one was for charging the battery - the other was to power the lights. The voltage was low on both windings, but was over 25 volts AC at 3000 rpm to charge the battery. However the output to the lights was only about 3 volts (just barely made them glow). The stator had been replaced by the Yamaha shop, but they were at a loss as to why the output was so low. I installed a used flywheel and not only did the lights work, the engine started easier and had more power. In almost all cases where I have seen one spark just as the starter button was pushed and sometimes another spark when the starter button was released, the problem turned out to be a faulty stator. The spark was caused by surge, but, one time I did find a weak flywheel. It's rare, but it does happen.