my yamaha blaster keeps blowing pistons what causes that?

[porkchop]

it has been bored out to a 67.5mm but i can ride for about a month and it does the same thing

 

[BC outside]

have you had the engine tuned? sounds like too much or lack of fuel

 

[Mitt Penetrator]

retard shouldn't own a machine if he doesn't know how it works.