Could be many things.
1. Plug
2. HT lead or coil
3. could be CDI
4. I was try in that order but it could be something else. It has stood for a long time so it is a case of replacing bit by bit. Was it inside or outside? 5 years is a long time so also change oil and put clean petrol in it which includes a carb strip!
bb
July 2009