HELP! The Magneto on my 1979 PUCH Maxi 2-speed _was_ working fine, but the other day I changed the Transmission fluid and now the magneto doesn't move or anything. When I pedal and engage the clutch, the magneto doesn't move and there is a massive ammount of drag on the bike. So it feels like it is trying to go but can't. I don't want to keep trying because I feel like something is going to break. How do I fix this?