I've read through all the hard starting threads on the KLX but didn't find any issue about the starter jet being the common problem. I got my '06 KLX250 last August and haven't had any of the cold starting issues...until yesterday. That was the first time the temp was in the 30's during a cold start. My KLX's valves are perfectly set. The fuel is clean, fresh, 91 octane. The bike was ridden just two days earlier on Sunday. The air filter is clean, and the plug is clean and gapped properly. The battery is only a month old and spins the motor with authority. The fuel level is set using the "clear tube" method outlined in the shop manual which indicates an absolutely correct fuel level.

My bike has always fired right up using the choke. Yesterday when it wouldn't, I thought of all the solutions that had been mentioned here. The one that worked was the issue of opening the float bowl drain screw. I left the fuel tap on and only let enough fuel out of the bowl to splash a tiny bit in a pan...and I mean a tiny bit...not even enough that would fill the bowl. All I wanted to insure was that fuel was in the bowl. I mean it had only been two days, and I did not turn off the fuel tap when last used. I attempted to start it, and the bike immediately fired up. Scratching head and wondering how that made one iota of difference.

This morning the temp was in the low 30's. I attempted to start the bike several times and no luck...same as yesterday. I cracked open the fuel bowl screw again for just a second to let out a few cc's of gas. The bike started immediately. OK...this is getting weird. It was almost like there was some kind of vacuum lock on the fuel getting into the bowl, but when you crack open the drain screw, it would disrupt the vacuum. Now I can't picture any kind of vacuum in this particular scenario, just the oddball idea that comes to mine. Why this method worked in my case is not clear...at least to me. It's not old fuel. It's not fuel evaporating from the bowl between uses...the fuel tap remains on. What is clear is that the engine is not getting enough fuel for a cold start.

I ran this scenario down to a buddy of mine who's the head mechanic at the local shop I used to work part time at for about 15 years. This guy is a mechanical wizard on most anything. After some thought, he reminded me of a cold start issue and fix on some of the new bikes through the shop that had occured. Every once in awhile a model will come out that is a cold start bear. Occasionally the fix has been to drill out the starter jet a tiny bit in the enrichening circuit to flow more fuel when the choke is on. The starter jet is usually a pressed in brass piece in the enrichening circuit. It's almost always non-replaceable, so you drill the brass out to the next carb jet drill size. Most shops have a carb jet drill bit set, and you use a little hand drill bit holder to do the job, not an electric drill. Not all carbs are designed where you can get to the starter jet with a drill bit, but many are...don't know about the CVK34 on our KLX's, but I'm going to check. The starter jet only works when the choke is operating, so drilling out the jet won't affect normal engine operation. Anyone ever heard of this before?

Anyway I'm going to look into it. However, I'm still perplexed by the issue of how/why cracking open the fuel bowl drain screw can have any appreciable effect on cold start-up when all the fuel quality, fuel level, and evaporation issues do not apply.

Edit: I just found a view that shows the starter jet facing straight out the bottom of the carb (inline with the main jet), so it looks very accessible.

 

Any chance that there is some moisture in the gas? It would settle in the bottom of the fuel bowl. I had that problem years ago on an outboard motor with three carbs. The lowest carb would get the water.
Shut the gas off. Drain the carb bowl. Disconnect the fuel line. Use a clear jar to collect some gas from the tank and let it set for a couple of minutes and see if you get water in the bottom of the jar.

Ride on
Brewster

 

Fuel is still in the bowl but all the hydrocarbons have evaporated as the bowl is next to the hot engine when you shut it off..

Solution:Turn the fuel tap of as you stop, then allow the bike to run the carb' dry (the revs will start to rise as the mixture becomes lean, shut it down then.)
When you turn the petrol tap on again, you'll always get fresh fuel in the bowl.

 

Interesting theory, but yesterday when I got the bike started, it only ran for less than a minute before I shut it down. No engine heat...no heat from weather, temps in 30's F...nothing trying to atomize the fuel. Also this problem would become more pronounced in warmer weather. They appear to get worse the colder the temps get...which does fit with a cold start fuel delivery.

Brewster, no water. Today when I caught that fuel out of the drain hose, I looked at it closely...no evidence of water and gas...just gas. It's a good thought, but I notice from studying a picture of this carb that the starter jet doesn't extend very far into the bowl. The water would logically be down in the bowl...unless it was mostly water...which doesn't appear to be the case. I don't know...fascinating but aggravating symptom. I'm leaving in the AM for our annual state enduro race at our riding area that our club puts on this Sunday. Otherwise I think I'd drill out that starter jet.

 

Whether or not WestOz's theory is correct, his solution is.

Emptying the bowl before you kill the engine worked for me.
No issue since going to the pumper and I have never had this problem with any 0ther bike.

I agree that it was worse in cold weather.

My theory is this.
Life started out as a single cell and using evolutionary principles and natural selection has progressed to the complex life forms we see today.

 

My bike has always been a hard starter.
I did exactly what you did, spoke to a buddy who works on bikes all the time, and is a mechanical genius. I've been a mechanic for 30 years, but not on bikes. Sure enough, as soon as I told him what was happening, he told me that they open up these jets on the carbed sport bikes that they build, and cam up. Once you put really aggressive cams in them, they don't want to start. Open up the jet (I think he said they open them up .005"), they fire every time. If you can post a pic of that drawing, I'd like to see it.

 

Two day break from riding the bike will still cause the bike to start hard. Run gas out and it will start everytime.

 

But you shouldn't have to.
I've never owned anything that was this difficult to start when cold.
There has to be a problem, and solution.

 

Well....yes I agree you shouldn't have to, but why fight it until the "solution" is found? Some things in life are a mystery.

 

Oh and yes there is a problem and a solution.

The problem: The bike won't start if it sits with gas in the bowl for days or weeks.
The solution: Run the gas out....

Sorry I just had to.