Why two-smokes hole pistons:
1. Weak mixture
2. Incorrect grade of plug
3. Incorrect timing
4. Using pre-mix oil in the petrol of a bike with an oil pump (causes weak mixture)
5. Using very old petrol which has lost its octane rating (bit of a long shot, but hey! you never know)
Number 1 could be many things, including air leaks in the inlet, crank seals or even air leaks into the exhaust which can make it run weak. The fact that it will not tick over properly suggests an air leak somewhere and this is what I would be looking for first.
