Had this issue since I puchased my 2009 KLX250S almost 2 years ago....would like to fix it once and for all so your advice is greatly appreciated.
Once bike is started and running it takes at least 5-7 minutes of idling until I can ride off without it hesitating to the point it will die if I don't baby it.

Background......

*Purchased slightly used in stock condition.....168 miles on the ODO.
*Bike ran bad from start.......hard to start, driveability issues until fully warm, sluggish under throttle.

*Installed Dynojet kit stage 2......groove #3, DJ128 main, fuel mixture out 3-turns.
*PowerBomb header
*Q4 exhaust
*Uni airfilter
*KDX snorkel
*Drill out enrichment jet
*New plug

Huge improvement and great ride after the above installs.....but stil have the driveability issue until fully warm.

Any ideas?

 

Remove your pilot jet and give it a good cleaning.

 

What part of the world are you in buerk, and what are the ambient temperatures there?

I find that I have similar symptoms when the whether cools, according roughly to this scale:
- below -10C, bike does not start
- between -10C & 0C, bike starts with considerable hesitation and takes up to 10 min to run well
- between 0C & +10C, bike starts with limited hesitation and runs well within a couple minutes
- above 10C, bike starts and runs immediately exactly as it's supposed to

I have done every mod, adjustment, and cleaned everything that could be related to cold starting & running hesitation and I've come to accept it's just a cold blooded b!tch.

 

Forgot to mention adjusting your fuel screw out a bit as well.

 

If the fuel screw is already out 3-turns don't you think he should go up a jet size?

 

Yeah, I overlooked that he is already 3 turns out. Either the pilot is plugged or he should up one on the pilot. I am guessing its plugged as the stock pilot works fine on my 331. And many on here have gone bigger on the pilot only to return to stock.

 

"stil have the driveability issue until fully warm."

Sounds like a temperature-related. If it were strictly jet size, or screw setting, I'd think the drivability issue would persist once the bike's warm...

 

Sounds like it has to do with your pilot jet.

Some people can run bigger pilot jets ( sea level, super high flow exhaust and air box )

My bike ran perfect with all the mods until I added the big bore kit. When you do a big bore, I was told to go bigger on the pilot. So I went to a 38. Bike ran great, started super easy, idled really strong, until it got warm. Then it would start to surge at idle. I adjusted everything I possibly could, including even going to a 40 pilot. It would still surge. However with the 40 pilot, I didn't even need the choke. So I went back down to a stock 35 and the surging went away. Bike runs fantastic, except for a weak idle when cold. It takes a good 5 minutes for it to idle smooth.

I need like a 36 pilot jet to be perfect. However one doesn't exist. Now I am at 3500 ft. elev. so I don't need a bigger pilot.

I bet if you went to a 38 pilot, your bike would run a lot better cold and have a better idle.

 

My brother has a set of jet reamers. You may want to look into them.

Went 351 kit and run a stock 34 pilot with about 2.3 turns out on the fuel mix screw. Choke on for about 20 seconds, then off and idles fine.

I wonder if the float setting could cause this too? Don't know...just throwing it out.

 

On your float concern...yes...you should always start with insuring your fuel level is at factory spec. It can cause grief that will have you chasing your tail trying to fix it with jetting. You should use the fuel level method than the physical position of the float. All you need is a piece of clear chainsaw/weedeater fuel line to connect to the drain/overflow spigot and hold it up to the side of the carb body with a fuel supply feeding the carb...much like the way the shop manual indicates but without the factory tool. Your problem may not be fuel level, but without removing it from the suspects, you may waste a lot of time.