Scooter 50cc won't start

Hi
Never had a scooter before so my brother in law has been trying to work out why my scooter won't start.
It's had a new carb, new air filter had piston rings replaced and still not starting. Had a service 2 weeks before it broke down.
It's a boation 50cc no idea what else it could be.
Anyone ideas?
Thanks

air filter you dont tend to need to change these for a derestrcition , so put the old airfilter back on to start with. you tend to change the airfilter when you fit a bigger cylinder kit.

does it have a spark ? check the sparkplug is sparking when scooter is turned over.

make sure you have connected the vacuum line to the fuel pump. without this fuel will NOT flow into the carb and on into engine. there are a couple places its usually connected to, one is the crankcase ( small black tube that leads to the fuel pump ), or the carb/carb manifold to the fuel pump. the vacuum created by the carb/engine opens the fuel valve and allows fuel to pump/drain into the carb.

Valve timing/ clearances

Thanks.
But the bike won't actually turn over. Wouldn't even kick start. Had new spark plug and it was sparking.

You dont have the bike running to check them....

If the valve timing is wrong your piston will smash into the valves and lock the engine up