hello,i have a 125 4stroke pit bike (chinese import) and it has started to develop a problem.it runs and starts ok but has started smoking very badly and i have noticed it seems to be burning the oil up.does anyone have an idea what has happened?
Valve guides and/or piston rings are shot. Depending on the engine that is in it you may be better off either just getting a new bike or picking up a new engine. Many of the horizontal engines are basically Bic lighter pieces (disposable). There are a few quality names to look for if you decide to replace the engine. Lifan, Jialing and Zongshen.
As Patman said, Lifan, Jialing and Zongshen are your engine options. I went with a 138cc Lifan two monts ago and it has been flawless. I should add that I had to use my carb and had to buy an oil cooler.