i got a Yamaha blaster 200 it rode fine the first day the next day i started it rode around the block and it wont start all it does is backfire i changed the spark plug and it still wouldnt start so i pull started it and it started but when i stopped and held in the clutch it stalled and it does the same thing

 

replace gas and be sure to use high octane. and a good two stroke oil mixed about 40;1

 

You might try cleaning out the carb and check to make sure the plug is getting good spark.