Piaggio liberty 50 4T 2009 problem

The bike starts first time of the kick start and will run for about 10 15 seconds. Then it will start bogging down eventually dies. Kick it over straight after fine again for same amount of time then same happens. Iv changed the plug as the plug was black and still having the same problem. My friend used it before hand and it was fine apart from one stall which then started again and was fine after. Anyone have any idea what it could be causing it. Thanks

 

Sound like it's running way too rich if the plug was black. Have you tried rejetting the carb?

 

Valve clearance?