LOL, you need to look the crf150r up then. But you should probly stick with a two stroke when the engine gets that small. They need to be around 11,000 RPMs for them to work, about the same as a 250f. Reliabilty is def. an issue when you start making modifications to an engine that small, esp. the high lift cams and a rev box. No doubt they are fast as sh*t, but they arent worth the extra money. Both the 85 and the 150r need to have the sh*t revved out of them to make power, so you might as well learn how to ride correctly with a two stroke while you are young and then get a 250f when you are ready.