Recently bought an kx250f and sounds to me there's an unusual noise from the engine.I've checked valve clearances (in spec) oil level,timing and everything looks good.any other possibilities?

 

Listen carefully, maybe get a long handle screwdriver or mechanic's stethoscope, put the tip around the engine and listen. Wherever the ticking is loudest is where your problem is.

ON a lot of other bikes if the ticking comes from the cam drive area the OEM tensioner is not working right anymore. The best replacement is a manual tensioner so you know how the adjustment is. I make them for the KLX and I believe I have one that will work on the KX250 too. I'd be willing to make a good deal on one if you need one. PM me and we can work it out, depending on where you're at it could be as low as $30.