I suggest that you start by looking at the spark plug. Take it out and see if there is a gap between the center and side electrode and make sure it is clean. If dirty clean with a cloth and wire brush or better still replace it. Replace the plug and try to start. If still will not start take plug out again and see if it is damp with petrol. If it is then problem may be the HT coil.
Maurice, April 2009
