2 days ago I excitedly purchased and rode home a KLX250sf with the 351 big bore kit and full FMF system. I rode it 130-140 miles. Into the journey the turn signal got burned up by the exhaust, and I mean really burned completely off, but I thought nothing of it because I had read about such problems with the exhaust burning the signal.

Then today I'm looking at it closer, and I noticed the inside of the exhaust seems to have melted a bit, this is where I get concerned and dig deeper. I have the dynojet box that came with the bike, so I look what jets are left in the box to figure out whats in the bike.

It's a 120... 120 is for stock air box (mine has snorkel removed!), and more importantly NOT taking into account the big bore at all!!! DJ instructions spec a 128 for the snorkel removed, and that still doesn't account for the 351, people say more like a 132 jet is necessary.

And since it was all highway I have a feeling I was on the main jet a decent amount doing 70ish MPH...

Is my new baby destroyed?! I am so nervous that it's been damaged by this ride, plus who knows how long the big bore has been on with the wrong jet. Please anyone with experience let me know what may be lurking inside the engine... I'm so scared...

 

You need to remove the carb and see exactly whats in there first.

 

Every jet (including the stock Keihin) is left in the box except 120, so I'm quite sure 120 is what's in there...

But I'll have to pull the carb and check before I'm riding it again, so I'll see what's in there either way.

Operating under the assumption a 120 is in there though, I'd like advice on how lean that is for near sea level (rode from New Jersey near shore to my hometown near water as well 275ft elevation). And how likely there is to be damage, or is it not as bad as I was thinking and may just get lucky and rejet it and be fine??

 

Is it the stock exhaust ? I wouldn't freak out too much.

FWIW my 331 with the 132 DJ was pig rich even with the airbox lid totally removed and I run a 128 DJ, the same as I had with the stock bore.

 

I'm starting to calm down a bit over it... Full FMF system on it though btw so you'd think it'd need a big jet.

I just called the previous owner (bought it from a dealer but his name was on title) and he says a shop did the big bore install and it's a well known shop with good reviews so maybe they put in a jet that was bigger and didn't put the old one back in the dynojet box... I'm gonna have to just pull the carb and check.

That leads me to mask, how hard is it to pull a carb on this bike? It looks like it's hidden in there pretty well, any guides here on the forums or is it simple and I should just take stuff off till I get to it.

 

Also keep in mind If it was that lean you would have a bog and noticeable lower power. If it was a 2 stroke then you would really have to worry but not so much on the 4 stroke.

 

Pull the spark plug and look at the color of the insulator around the center electrode. If you have a magnifying glass, check the tip of the center electrode for little ***** of metal.

If the insulator is lighter than light tan it is too lean. If you see little ***** of metal, that's pieces of the aluminum piston that have boiled off the piston crown. That is NOT good.

 

Carb removal: Kawasaki KLX 250 slip on - HMF Engineering Forums

Lots of other good stuff in this thread: https://www.kawasakiforums.com/forum...q-links-30733/

As mentioned above, pull the carb and plug and have a look. If you're worried after looking at the plug, perhaps find someone with a bore scope that can look down into the plug hole for an inspection of the piston.

Good luck!


Edit:

Here's a jet conversion chart: https://www.kawasakiforums.com/forum...e2/#post442610

DynoJet and Keihin jet numbers are very different.
The stock 118 Keihin jet is approximately equivalent to a #112 DJ
The #120 DJ is approximately equivalent to a #128 Keihin.