Check all the head bolts, carb bolts, exhaust bolts are tight, disconnect the kill switch completely, check the coil wires are undamaged including the plug cap and remove the throttle linkage.
Check the carb settings are somewhere near the factory settings, turn up the idle and try again.
2 or 3 pulls with choke on then choke off to start it.
If u flood it, remove plug, turn upside down and pull pullstart a few times.
Shine a torch into cylinder to look for damage ?
You can put a drop of petrol in cylinder, replace plug and try too, if it starts then it may point at the carb, are the petrol lines on the correct way ?
Cheers
Dave