I recently purchased a 2013 klx250s and It has an fmf q4 slip on exhaust. As far as I can tell this is the only modification to the bike that would affect performance. The bike will run fine on top end but spits and sputters on the low-mid range. I can ease on the throttle and it will run smoothly thru the rpm range but a quick snap will result in either spitting and sputtering when warm or the bike going dead when cold. It will idle fine but must be choked to get it running from cold. The carb is spotless and best I can tell the jetting is all stock. Looking for ideas. Thanks!

 

Area to check is the (entire) pilot system functionality.
Specifically:
The many orifices of the pilot jet - they must ALL be clear of obstruction(s).
Fuel screw setting. screw must be functional (its' ports unobstructed) and set correctly.(2 - 3 turns out depending on the altitudes your bike will see..)
Float (fuel) level in the bowl must be correct (use clear tube method to check that the fuel level is just above bowl/carb body mating surface, IIRC..)
Pilot system transition ports - directly implicated by your symptoms - Every one of these ports must be unobstructed. if these tiny orifices are blocked, anything more than a gradual throttle change will have a bog.

Buying a used KLX that needs carb work can end up requiring you to become a CVK "expert"... If you hire the work done, be sure they know enough about CVK's to be able to point out (to you) where the transition ports are, before you leave your carb with them ! (They are in the carb barrel floor, between the slide and the butterfly ..)

Good luck !

 

Thanks for the advice, I’ll definitely check again. Everything was exceptionally clean when I checked the carb. I didn’t clean with my cleaner or any chemical based cleaners, only air do to time and the fact that it was very clean upon visual inspection. I could have very well missed something but I wanted to see if it could’ve been a bigger issue before I started trying to rejet which is something I am not familiar with. I can normally work my way thru most things carb related but I may have assumed to much because of how clean everything looked. I hope that’s all it is but if not I’ll keep you posted. Thanks again!

 

My pleasure.. BTW, if you intend to install a DJ jet kit ( DJ2152) , now would be the time to do it as you will be dismantling your carb to run the proper checks and verifications on the pilot system. Since it'll be apart, might as well dismantle the primary fueling system to check the emulsion tube pin holes and all the other primary fueling system passageways (MAJ, etc)..

 

I would just like to add..... Yes... you do intend to do the jet kit. Totally different bike properly jetted