Yamaha Blaster spark plug failure?

My blaster only goes about 20 km on a new spark plug then it dies. And will not start again. When you replace the spark plug with a new one, it starts and runs fine for about the same distance before it dies again. The dead spark plugs looks fine but there is no spark. I've heard it can be an electric surge or something. Any help on what it can be and how to fix the problem?