i have a 09 klx 250s i just reread the free mod that everyone talks about, i pulled the air box cover off sounded "different" but i gave it a go. ran like crap so i put it back on but left the snorkle off, much better ran with more seat of the pants power. next is the stock exhaust if i understand i take a 1/2 long drill bit and drill through the first baffle right thru the center of the exhaust i'll give that a try. thanks for all the info i got from lurkin here. if anyone comes to the wht mtn. of arizona look for me waving

 

They say the bike comes lean from the factory, so without rejetting the bike only gets leaner when taking off the air box lid or snorkle.. So in my opinion, you should re jet it too..

 

+1 on the rejet.

 

Im Pretty unfamiliar with the stock exhaust mod.. Is that worth the trouble or no?? Plz let us know how it goes

 

From what i have heard this is only on the 300 exhaust but it could hold true to the 250 exhaust too. they weld on the inside of the header oposed to the outside and that in turn makes the diameter of the header smaller. in the whole scheme of things the stock 250S sexhaust is smaller than that of the 300. i did the grind on mine and i didnt feel anything but i guess it could have. i anyone plans on doing this i do give a caution sign becarful of your bit heating up and be carfull not to go to far or you will have to get your flange re-welded.

Inreply to arizona gamebird, you are right there are some free mods that you can do to unlease the bike a little bit. This intales getting a Dyno-jet kit and that is where most mebers have gotten the airbox lid removing idea from. the next would be taking all the smog crap off that is all your option it tends to rob a little horse power. next would be invest in a decent airfilter, twinair is nice but that is only because that is what is in my bike, your choice. Some have dont this i dont know if it really affects the 250S much but my dad and i did this mod. below under your airbox there is a hose that runs to the crank case. some members have drilled out the plastic on the airbox to get better airflow. this is a mod done to the 300 so there is minimal pressre within the crank case. good luck and have fun.