Woundering if any one can help I have a 57plate aerox 50cc scooter all standard appart from a handmade tt sports exhaust my brother had it before me and all was working fine it has done 12k with a recent service and all ov a sudden it has started to miss fire lag and loose power when hitting 50kmh any guidence greatly appreciated

Have you tried a new spark plug and cleaning the air filter ? Was the exhaust on the bike when your bro' had it ?