I decided to do an oil change in my 83 200x today and did it like I always have. I started it up and everything was normal. It was warming up when I turned around and looked into a wall of blue smoke. I revved it up a bit but nothing changed. I turned it off. I took out the spark plug and smoke came out the hole. I put the plug back in started it up and eventually it quit. This never happened before. Does anyone know what happened? Thanks