does it have a spark. Check this by taking plug out and put in cap then place on metal cylinder or frame. This will earth it and it will spark. should be nice and blue. If not spark then look at HT lead and coil.
if there is a spark put a little bit f petrol down the spark plug hole. and try to fire it. Should fire. If it fires and then stops I would suspect your carb. No petrol getting to your bore.
Good Luck.
BB, June 2009