Dirt Rider Magazine

I am new to the 4stroke world. i just bought the bike and noticed after a good riding day when i killed the engine i saw a little water under the engine. It looks like the over flow on radiator. I bought the bike from a dealer and a buddy of mine stated his 4stroke would do the same thing. Just making sure if this could be normal. I am not running race gas but i am running treated gas. is that a bad idea?. Race gas is 9 something a gallon and i ride alot at the house, or should i just get non ethonal gas?