Thank you to those who posted previously on how to fix the cold start issue on early model KLX 250S. I successfully completed upgrading the pilot jet from OEM 35, to a 38. And drilling the enricher (choke) jet to a #76, (.020). I know many have had success with a #77 (.018), yet I wanted to really give the carb an easy time getting fuel to the engine.

Unfortunately, I did not find the enricher fix until after installing the larger pilot jet, and had to remove the carb (fuel lines, linkage, etc.) a second time. Ugg!! I have a few choice words for whomever designed how to remove/replace the carb.

NEW INFO: What I found missing from other posts was the details of drilling out the enricher jet.

1) The jet is about a quarter inch down from the enricher opening.
2) The drill bit is about half the width of a human hair. There are Pin Vise Hand Drills designed to hold these bits. I used a small pair of hemostats to hold the drill bit.
3) This is a blind and delicate, yet doable, procedure and you have to "feel" your way through it.
4) Make sure you are comfortable and have the time to focus. I did mine by cradling the carb between my legs while sitting in my recliner. I then rested my left hand on the carb and held the tip of the hemostats between my thumb and index finger for support.
5) I then very gently and slowly twisted, checking by pulling up, to see if the bit caught the metal. Once it caught, I'd back off a little, advance, back off, advance, repeat until soon I could simply raise and lower the bit smoothly in the enlarged hole.
6). I blew out the jet with carb cleaner.

So nice to feel I can trust my bike to start!

Hope that helps someone.

 

Alternatively, install a #38 or #40 pilot jet, set fuel screw to 2 turns out on the #40 or 2.5 out on a #38 (if near sea level), start engine and allow to warm up to full operating temp - set idle speed to specs (target 1250 rpms)..

Always drain a little fuel out of the bowl, before starting, if it has been 24 hrs or more since last startup..

 

And yet some of us, particularly those at higher elevations, find snappier off-idle throttle respond with the stock #35 pilot jet with the fuel screw about 2 to 2.5 turns out, and better starting with the enlarged enricher jet. The larger pilot jet just bogs off-throttle response.

 

Agreed, for a bike that is always at higher elevations (4k-5k ASL and up), a larger pilot jet is not called for and drilling the enrichener jet would make cold starts easier... For the rest, the #40 and #38 along with a correct idle speed will usually suffice.