It is stuck. Thats all. Tap on flywheel. Put the nut back on a couple of threads to tap it and not mess up the threads. I like to tap and (put pressure up with other hand) on flywheel. When u put it back, use a very slight amount of anti sieze on mating surface of flywheel. Like the size of a rain drop.

A little bit of anti sieze goes a long way. You could also lighten the flywheel at this point. However, lightenning the flywheel is great for WIDE open running put not closed course racing. The flywheel weight will actually help carry you through the turns and keep RPM`s up. If your running a larger track where your almost always on the hammer, lighten the flywheel. Use a balancer for a lawn mower blade to balance your flywheel.