2006 and newer are all the same. I believe someone even stuck a bill blue big bore on a 1999 KLX and it worked without too much modification.

Anyways, yes, carbs and engine are identical. Jet kit will work on the stock carb / big bore combo. I still have the stock carb on my big bore.

My advice is install the jet kit with your exhaust mods first. Get the bike dialed in and then install the big bore. Many people find the big bore doesn't change the jetting at all. I changed my jetting when I installed the big bore before I ever fired it up. Jetting was off a bit, went back to my settings before the big bore and it runs great now. In the end, all I ended up changing was going up one size on the main jet. Everything else stayed the same.

 

To answer your original question about durability, I think it comes down to the type of riders and the fact there is no manuals to doing this, you are on your own.

these bikes are built to run forever, many of the people who come to this bike have an MX background or have owned and MX bike previously. those race engines are built to the nuts and any change like a big bore can cause some additional wear and tear. Plus, race bikes tend to wear out much faster anyways. So people are hesitant about changes like this.

the big bore on the KLX doesn't seem to harm it in any way. It has had quite a few years to prove itself now. Other than smoking a couple clutches and a bad install or two, many have been great successes.

I am pretty easy on the clutch, and after 3000 miles, my bike rides great. No problems whatsoever caused by the big bore.

 

Thanks BigSky,yes my plan was to install the exhaust first along with the dynokit and maybe take the airbox cover off,not sure about the cover though,once the bike is jetted properly it wont damage the bike correct? I ride about 90% on road and what little ofroad is never watercrossing or even trails,just a few dirt roads but is it better for the bike to just get a larger snorkle or maybe cut a hole in the top of the airbox cover?
Thanks,
Hunterman.

 

No matter how you have the bike jetted, it is better than stock and you really can't hurt the bike. Follow the dynojet rules, they are usually pretty accurate.

I don't like the bike with the lid off. For starters, they start to do weird things with the lid off and they are harder to jet properly. Plus they are LOUD without a lid off them. I went with a KDX 200 snorkel and drilled a few 1/2" holes in the lid and it works perfect.

 

I'll put my 2 cents in the mix. I have the 2010 and I put the kustom Kraft 330 on mine. I did the kdx 220 snorkel , stage 2 jet kit with the 132 jet. Also I have the DG Exhaust slip-on with quiet core. The only down side to the big bore kit is you will get less mpg. I'll still in high 50's , low 60's but I'm still playing with the new power.

 

Come to think of it, I dont even remember reading about anyone who "wore out" their big bore KLX250 yet. I have read of multiple people with 50k+ miles on their big bores.

I think the big bore is pretty reliable, probably other parts of the bike will fail first.