as i am a fitter working on lawnmowers i might be able to help but you have not really give me much to go on. but most magnets on flywheels are built into the flywheel you can check by putting something metal against the outside circumfrence of the flywheel and if it dont stick your magnets are u/s and you will need a new flywheel
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Try fixfault.com to fix lawn mowers.