The coil (the black roundish thing which connects to the spark plug) might be broken and needs to be replaced. Or there might be a loose wire. Or there might be too much corrosion inside the spark plug cap. Use some WR40 spray or similar or if it's really bad you might have to replace the whole cap.
If the spark plug is old and sooted up, you can use some very fine sanding paper to clean the nodes on it. Or just buy a new one. Which I myself find much more convenient. It costs almost nothing anyway.
These are some of the possibilites.
Espen, August 2007
