Haven't taken carb off yet (07 KLX250S) but need to know the style/type of main jet to ask for at the dealer. I have a UNI filter, snorkel removed, will have HMF muffler, FMF header. I am in iowa. I have been told a 120 main, 2 turns out on the mixture screw. I don't really want to shim the needle if i can avoid it.
Anyway, suggestions?

Mike

 

Are you using Keihin jets or Dyno Jet Jets? Because they aren't the same.

A 120 Keihin is way too small, even a DJ 120 is too small. I believe most of the guys here that run keihin jets run up in the 130's and most of the DJ guys run 124-132.

You can see my info in my signature, but I basically have the same mods as you and I run a 124 DJ main. Now I am at 3300' elevation so I jetted a little smaller. If you are running a DJ jet, I would guess a 128 main at around your elevation. You can also order the N1tc needle from your dealer and not have to use spacers.

Don't forget to drill the slide either.

 

Pretty much agree with all that Big Sky stated. You're going to want to change that needle. The OEM needle has a lousy profile for any performance. I prefer the DJ needle, but both the stock 300 needle suggested by BSK and the DJ needle are head-and-shoulders above the OEM needle. If it's mileage you're worried about, my '06 250S with a 300 jug, DJ needle jet kit, airbox mods, and Muzzy pipe will get mileage in the 60's on pavement with consistency and once got a low mileage of 47 that had 20 miles of deep, sandy trail involved. Normally off road I can count on about 55. Proper jetting, even though numercially richer, will provide equal or better than stock mileage if it's done right to match your mods. Even with a 300 jug, I'm running a 128 DJ main jet, and it's perfect for my altitude of about 1500 feet. I just got back from Colorado where it carbureted cleanly all the way to 12000 feet, and only started some minor chugging as I approached 13000 feet and above on Imogene Pass. These CV carbs have tremendous lattitude on their high altitude performance as it applies to jetting.

And yes...drill the slide for improved throttle response. The stock jetting setup absolutely sucks...don't hamper yourself by living with it.

 

BigSky and TNC are the experts. Do what they say.

I have an 09 and followed the Stage 2 Dynojet directions, took out the snorkle (after trying to modify it several ways) put on an HMF with Quiet Core and spark arrestor, ended up with a 128 main, Dynojet needle, and I put in the weaker spring instead of drilling the slide. I bet I'll end up drilling the slide the first time that spring isn't strong enough to shut the slide! I really think drilling is smarter than what I did. Kouba screw for elevation tuning...set at 2 turns out, I believe. I'm riding at 2200-4000 feet.

Anyway, I rode it off-road 90% the other day, with some really tough hillclimbs, 5% was WOT into a 30-40 mph wind on the road to finally get to 60 mph, and the other 5% was getting home on the road. I got 53 mpg. Bike now has 430 total miles on it....so, it might get better if it loosens up. Oh, running 20w-50 in it, which is a bit thicker than needed, probably.

 

Blackheart, you run a 128 at the higher elevation? I am just curious because everyone seems to be lower but you are actually at a higher elevation like me.

Any soot in the pipe? or bogging with the 128 ? I have contemplated switching up from a 124 to a 128 but it runs pretty good at 124. Maybe a hair on the lean side but no popping or anything like that so I got to be close. After 400+ miles on the 124 jetting, my spark arrestor still looks brand new, not covered in soot.

 

Well, I only have 75 miles on this new setup, so, it's too soon to say....no soot, yet.

However, I don't have a snorkle at all. That KDX snorkle you have is much more open than the stock snorkle...BUT, if there is ANY increase in resistance to air moving into the carb with the KDX snorkle compared to NO snorkle, this higher negative pressure in the throat of the carb essentially makes your smaller jet to FEEL more suction...which makes it act like a slightly bigger jet. At least, that's the way I understand it, and is one of the reasons why you have to put in a bigger jet when opening the air intake up (assuming you unplug the exhaust to be able to move air out of the way more quickly)....and one of the reasons why the fuel mileage doesn't necessarily plummet just because you went to a bigger jet.

If I don't have that relationship correct, I'd sure like someone to teach me more about it.

I was very pleased with 53 mpg on this initial run. Don't know enough yet to tell if it's too rich or lean. Gonna do the poor man's Spark Plug Eyeball test to determine if it's close enough or not.

 

ask for small round kiehin, don't let them give you a mikuni jet that is real close to the same physical size and shape , one of the tip offs is the mikunis come in .5 sizes (127.5 etc), so if the case their pulling the jets out of have 1/2 sizes it'll be wrong.