Hello all, new to the forum, picked up an '07 250 S basket case last fall for $500, spent all winter rebuilding it litteraly frame to bottom with new head, all new bearings, seals, timing chain, 300 top end. Not to get into much detail here. That is subject to a subsequent thread writeup with pics I took along the way.

I know this subject has been covered numerous times, for different combo of mods, big bores and exhaust. My situation is not unique, but I still need help/opinins from others who have done the similar OE 300 upgrade.

So here are some mods I have done:
-Cut out backfire screen
-Drilled airbox crancase vent to 3/8"
-Drilled carb slide 7/64"
-Shimmed needle about 1/8" with a few tiny washers
-Low speed jet adjusted 2-1/2 turns
-118 main jet swapped for a 128 main (for starters, also have a 132, and 125 waiting in the wings)

What is stock:
-all OE exhaust (will remain due to lack of further $$), may drill baffle, but will wait to figure out my jetting baseline
-airbox lid and snorkle remain for now, my put in KDX snorkel

I have had it on the road about a week now. It starts VERY easy, idles well, even at low temps, and goes down the road seemingly fine. But I am getting what sounds like pre-ignition under accel, esp at lower rpms. Even light to moderate accel. Not pinging, sounds more like a sharp knock/rap on each compression stroke. I pulled the plug, an NGK iridium (same heat range as stock), and after 60 miles or so it is completly white, leading me to think it is running lean. But it does not pop or anything like that under decel. So not sure.

Now, I have read about faulty cam chain adjusters causing noise as I describe. But my chain is brand new, and the adjuster ratchet teeth look fine. Hard to believe a fresh chain can make noise like that. May still spring for a manual adjuster.

But the overy clean plug has me wondering. Jetting seens lean. Should I replace the needle jet with the 300 unit? Same with 300 needle? Or am I better off with a DJ kit?

Does it sould like I am even in the ballpark? An advice I can get woould be most appreciated!
-Jim

 

DJ, hands down. Once you buy the kit, email them and tell them what your setup is. In a couple hours, one of their engineers will email you back with a custom setup.

I have made 2 changes to my bike, emailed them both times, and they have hit the setup dead-on both times! BTW - I can't just follow the "standard" instructions as I'm at 4,700 above sea level, and ride to over 10,000.

 

Your jetting should be close, you might contact dynojet and just act like you have one of their kits to see what they suggest. The timing chain issue atleast on mine happened between 5-6k rpms and I have seen others say the same. It was a rattle that could be heard over my powercore 4 exhaust which means it was real loud. You want to upgrade your stock pipe any way you can as the stock piece is as close to a boat anchor as any I have ever seen.

 

Thanks for the input guys. I might need to contact dynojet directly, as I don't see my application listed. Maybe I am missing something.

As for the stock exhaust, yeah, I know it is an anchor, but I am stuck with it, won't get a $400 exhaust approved by the finance dept.. Already spend alot on parts for this build.

Plus, Maine has some new law pertaining to exhausts, in order to pass road inspection, an OE exhaust must be on the bike. I think they may back off, same way they did with aftermarket wheel sizes on cars with abs.

 

don't waste time drilling the baffle, its not even a baffle anyway, its the spark arrester.

you need to replace the endcap on the pipe with something with a larger opening.

 

That makes sense. I always wondered how that mod would have any real affect considering the existing outlet is only about 9/16", and looks like something you would extrude a spagettii noodle with. My old Honda XL250R had an exhaust outlett at least 2x that dia. And that was stock street legal as well. I thought of using a holesaw and install some sort of finishing cap. I have a spare exhaust that I may experiment with once I get the jetting closer to figured out.

 

I did some research, and it appears the DJ kit for the KLX 300 might be my best bet, as there is none for the 250S. That is what folks are recomending in other forums.

The DJ kit contains 3 jets sizes, practically the same assortment that l already have, a drill bit and screw to remove the idle circuit adjustment plug (already done), a new spring, needle, clips, spacer, I think. I wish I could buy just the latter parts, as that is all I would need.

One thing I noticed, there is no needle jet included in the kit. I know the 250S version is different from the 300 needle jet. I wonder how critical that part is? Mayb that is something I will need to order from Kawi before doing anything else.

 

You could get one, though whether or not its needed is a different question. Theres plenty of people on this board who are running 331-351 bored KLX's on the 250 DJ kit in an otherwise stock 250 carb with no problems.

 

DJ 2152 is the kit for '09 and above KLX250s. Under $50 here...

DynoJet Stage 1 & 2 Jet Kit for Kawasaki KLX 250 S 09-10

 

Not a bad deal, though mine is a 2007, wonder what the difference might be?