When magnetos fail they often give you a bit of warning, one such warning is a misfire! Also the bike is difficult to start when hot. If you haven't given the magneto any attention it would be worth giving it a general 'service' which is in the scope of most owners and can be undertaken without removing it from the bike. i.e clean the points and check the gap, remove the pickups and make sure both brushes are clean and free to move in their slots, give the slip ring a clean whist the pickups are out, clean the HT leads and check the plug caps and connections at both ends of the HT leads, remove the earth brush and make sure it is free in its pod and not oily.
