Use FRESH fuel. Fuel more than 6 months old is VERY likely to case a non-start. Proof - remove air filter and spray some easy-start into carb. Start engine. If it stalls, repeat. If stale fuel is the problem, it will stay running after 3 or 4 attanpts (explanation - the heat buld up in the cylinder is enough to vaporise the poor quality fuel enough to keep running).
If there is no life whatever, assume an ignition problem.
If it won't run with fresh fuel, remove carb, clean, replace diaphragm.
phil_saunders(a)bigfoot.com
Phil Saunders, September 2009