magneto key problem

First of all, is your key a rounded bottom woodruff, or a rectangular woodruff? What I always do when installing a key is pop it into the shaft first, get it all lined up, then slide over whatever I want to slide on, over the key, be it a clutch, a sprocket, or in your case a magneto rotor. I highly doubt it is the magnet's problem if you have spark. what is your carb set to? It might not be right.

Installing woodruff key image by borisbulldog on Photobucket pretend this is your engine, the left arrow, the key, is what you put in first, then slide the sprocket (or magnet) in the right arrow over your key

the problem is the key always wants to jump onto the magnet when you try to slide it on.

a small drop of superglue works to hold the key to the shaft.