I'm going through the same issues. I installed a KLX300 exhaust and a KDX snorkel on my '06 250s a few weeks ago. I already had a UNI filter, and I went with a 124 main and 3rd notch form the top. My carb doesn't have an A/F screw, and I wasn't interested in drilling it. With that setup the bike worked great, but I got heavy decel popping. I changed my needle to the 2nd notch form the top, and the popping is somewhat better better, but I still think it's excessive, and it seems like the performance has dropped off a bit.

 

Rooster:

Are you saying your carb does not have an A/F screw, or it does but you didn't want to remove the cap preventing adjustment? My experience is just a little air into the exhaust from a small leak will allow decel popping, and not to worry about it.

 

Hey guys. I recently got an 06 also. Did all the mods pretty much at once with great advice from you guys. FMF slip on, smog removed and plugged, dj 128 main, 3rd notch, 2 1/4 out. uni filter lid off. 3/8 melt through for the cc breather, 13 t cs. Metzler mc6 knobbies. I use it as a dirt bike only. HUGE improvement over stock. Seems to run great with very little popping. I pulled the new plug just out of curiousity and it was light grey. I take it that means lean right? What would be the best way to fix that?Thanks guys.

 

Had a good adventure yesterday; just under 100 miles. I am pretty sure it is just decel popping instead of backfiring. The bike did well but I have a little issue with the idle or something on the trail. The idle/throttle seems to be sticking a little. At several down hill 'rock gardens' when I pulled in the clutch it would hang around 4000 rpm for a several seconds before dropping. My idle screw does not turn smoothly so maybe a little WD40 and a little tinkering with the T-handle can resolve this. What do you guys use to turn your T-handle? I have small fingers but still can't reach it without touching something HOT.
Water crossings were a little issue also; once I made it out the other side it would bog/almost die for a few seconds. Rev it up and it seemed to clear out until the next crossing. I may need to re-route some of my hoses and install the 'Y' fitting on a couple tubes like Dirt Surfer did. All in all, a great first ride!

 

My T-handle doesn't turn smoothly, and it shouldn't or it will back out too easy. Leather gloves. Do the "Y" mod.

 

Just reviewed several routing & Y mod posts; first thing on my to do list now. The T handle is seated well; don't expect it to work its way out on its own. Geeez, yup I'm sure a glove would help Thanks

Did not notice anyone Y mod'ing the hoses coming from the tank. Are they good to go as is; straight down to the bottom shock linkage?

 

132 and 40 and full muzzy, no air box lid with a slight popping on decel, but otherwise has ran perfect since 06. Elevation from 300 to 3000 no issues.

 

Make sure the glove is leather and not some poly stuff. I've also used a screwdriver or a little stick to help. I rarely adjust, but will when riding extended time above 8000 ft or so.

I've not seen anyone y-mod the tank hoses. I don't think the tank pulls enough vacuum to suck water unless you were riding submerged hoses for a long time.

 

Installed the carb vent lines "Y" mod and tested it through a couple creek crossing, so far so good.

The 'Y' fitting fit perfect behind the R Brake reservoir which holds it securely.

I ran the drain line from this 'Y' beside my R brake line.


I located the other 'Y' near the rear shock.

I ran both lines up and into the top of the air box.

 

fwiw, I was best fueling with a 128 foam filter, put a k&N in and went lean and jumped up to a 132. 300 pipe and uncorked 300 muffler made about the same power as a big gun I had to test with , at the same noise levels. (corked un corked etc). So not really convinced the headpipe diam made much difference at the stock 250 motor level hp wise. Might of had a little more low mid, but I usually blow right through those rpms riding the little motor.