The 13 tooth sprocket is for the off road as it makes the bike have better manners in tight stuff.

 

Dyno jet kit and KDX snorkel worked for me. Stock exhaust 60 Mpg. Runs great. Huge difference from new.

Thank you
David

 

I know this is an old thread, but I just had some mods done to my 09 KLX250S and wanted to share my results.
I had an FMF Powercore 4 pipe, Megabomb header, highflow foam filter, removed snorkle, and rejet kit.
The first thing I noticed is that the bike is MUCH easier to start, MUCH easier.
I was having hell getting the bike started, even restarting it after it was warm.
Now it only takes two or three cranks and its running good.

It also improved the bottom end power a good bit. Before the bike just felt like it was bogging all the time, the stock setup is VERY choked.
You can lug the bike down around 2500 to 3000 rpm alot better, it still has some power and will pickup rpms much better than before. Top end seems about the same.
Oh, and it sounds like a real bike now also
A good bit louder yes, not not horrible. Nice deep thumber sound for a 250 I think.
The stock exhaust was also alot heavier than the aftermarket stuff, so I saved some weight also.
~John

 

Thanks for the info on the 2009! Did you drill anything out?

 

I use a TwinAir. And lots of Maxima Air Filter Oil. The K & N will pass more air, AND small pieces of grit. Use a good foam filter with grease on the contact edge. And a good heavy sticky foam filter oil like Maxima. We ride in the desert and a lot of sand. Mucho Dusty all the time. Live and learn. A four stroke single top end job can cost a $1000 easily. Ask a KTM four stroke owner who has not serviced his air cleaner properly.