Could be water or antifreeze getting into the oil
Just save your money and look for a decent used bike for a first bike. There are lots of good used dirt bikes if you know what to look at when buying a bike.
dirt bike i would look for a 200-300 cc street i would look for a 650-700
look on the front on the frame you will see a vin numberwrite that down and call a dirt bike mechanic or call suzuki
look for leaks and craks and dents
Google "how to replace dirt bike tires" or look at forums at thumper talk http://www.thumpertalk.com/forum/showthread.php?t=390735
Justin Bieber's bike is a dirt bike. On the dirt bike it has a picture of him and his ex girlfriend. The dirt bike cost $10,000 which is a lot of money. The speed of this bike is 9 miles for 30 minutes.
I would look for a nice used yz125 to start out with. There are a lot of them and they were top of the class for a long time. The crf150 answer was stupid.
I would look at a Yamaha tt-r225 which would be comparable to a crf150r in power. The new Honda bikes are garbage, don't waste your money.
Those are just some dirt bikers, you can also look under "dirt bike dictionary" for more info on models, of dirt bikes and so on.
Sites I recommend to look at: Craigslist.com or other sites common to craigslist.com in your area.
It looked like a regular bycycle, but with a motor and just a little widthier than a bike.
nope the plastics are way off. go to http://www.jjwdesigns.com/ for the best graphics around... look good and tough as nails