My activa some times its stopping fuel is not comming to carborator after waiting 10 to 15 minutes again it will start why

How do you know fuel is not coming into the carb? Have you removed the fuel inlet pipe into the carb and checked?
1. If yes, i.e. actually fuel flow is stopping into the carb, sometimes, then your vacuum petcock(the contraption just below the fuel tank- which allows fuel to flow into the carb)is malfunctioning due to a leak in the vacuum pipe( the pipe which goes from the vacuum petcock into the engine inlet manifold).
2. If NO, i.e. fuel flow into the carb is NOT stopping - then get your carb cleaned, especially the jets - both main & idle. Hope it helps.