I think you are asking a lot trying to remagnetize that way. You need to use a very strong field, which you won't get from an ordinary magnet, and I'm not at all sure it can be done with the magnets already installed in the flywheel. I'm thinking in terms of using a really serious electromagnet, and probably doing it with the magnets separated from the flywheel. However I've never done the job, or seen it done.
Before you conclude that your magnets are too weak, you need to be sure that you have the points opening at the exact point of maximum rate of flux-change as the magnet passes by the coil. Remember you are looking for the maximum rate of change, not the strongest flux. If you have all the right parts in an engine, you achieve this just by setting the breaker points correctly, but when you don't have the right parts or don't know the correct point gap, you have to do it by trial and error. I've spent more than an hour doing it with an old Villiers engine on an Atco mower when I didn't know what the gap should be. Even then I finished up with a pretty average spark.
