When i rejetted mine for CO it ran great, when i came back i didnt even touch it. It ran better, Like you i think i had it rich, then i got it right on the money.

 

I'm at 300 and jetted at 132 and 40, it runs perfect right up to about 2000 ft, then it looses a little of its snap. But I dont get that high very often.

 

Glad you're liking it here...

I have the stock 250 bore, but I'm running exactly what your are (DJ120 = Keihin 128) right now. If I go lower (i.e. DJ116 = Keihin 122) mine will choke above 6000 RPM. I would *like* to try a DJ118, but they didn't include one in the KLX250 kit.

 

I'm convinced the vast majority of the "jetted" bikes are running excessively rich. It is much more difficult to determine an overly rich condition by feel and driveability than it is to determine a lean condition. It seems the consensus has always been that big jets will make your (insert vehicle type here) fast.

BTW, my 2006 has a 351. I'm running a 120 main (Keihin).

Ron

 

Ron, what kind of pipe and airbox mods, if any, are you running? Your main would be somewhere in the vicinity of a 114-118 DJ. If I ran that, I'd have detonation clatter out the wazzoo at WOT. I agree that many over-jet due to fear and/or lack of knowledge, but I'm amazed you can run that main jet. I also remember that you run a 300 emulsion tube, but that shouldn't affect WOT that much...just more in the 1/4 to 3/4 range, I would think.

 

The emulsion tube is a big factor for the mid range, but it also keeps working when up on the main.

I use a 300 muffler and pipe with a home brew tip:




My air filter is either a Uni or TwinAir. I have both, but don't remember which one is in the bike right now, but they are both essentially the same.

Air box lid is on with the OEM snorkel.

I've mentioned in the past that when I was fine tuning my main jet I did a number of consecutive runs with different combinations of main jets and snorkels (OEM and KDX). I made runs in two directions on the same section of road and recorded the highest speed reached. (Professional rider, closed course, do not attempt).

Here are my notes from right after the test runs:
"The OEM snorkel performed better in every test. On two of the runs where the average top speeds were the same, the engine was more linear and more responsive in the lower rpm ranges with the OEM snorkel."

The highest speed (90 mph) was attained with the OEM snorkel and a 120 main. There was more left, but at 90 I started getting a speed wobble and decided it would be best to slow down. I had D606's on at the time that were about 2/3 worn out.

Ron

 

Well...maybe I'll try bumping it down one more step the next time I take it all apart. Your's sure seems to be set up to be lean, though!

 

That's interesting, Ron. However, as I just commented on the other post, "clip position vs. jet size", we all seem to be running either slightly or even dramatically different setups from gearing, mods, and components. It's probably nearly impossible to attain exact plug-and-play comparisons to all of our bikes. My exhaust is different, I ripped out everything in the airbox (screen included), an OEM 300 jug, different gearing, etc. Probably even how I ride and where is noticeably different. I've given up on the concept of thinking there is a "holy grail" of jetting effectiveness unless all the potential variables were laboratory controlled...and a laboratory is a very small place to ride. I'm sure your jetting is probably spot-on for your setup, as I know you're serious about optimum performance from past dealings. I can assure you that if I ran your main jet in my setup, the clatter would sound worse than the loose cam chain that many of us have experienced. I did try that DJ main jet one step down from my current 128...too lazy to go dig out my box of jets to look...and I would get a subtle detonation rattle when cruising in top gear and then twisting to WOT. If I eased the throttle on, I couldn't hear it, but whacking it open resulted in "hearable" detonation for a few seconds. I'm pretty sure it was still rattling as speed neared full potential, but by then the wind, engine noise, and exhaust blotted everything else out. I can also tell by my mileage, that I must be just about right for best performance "and" mileage in concert for my bike.

 

Tend to agree that people do tend to over jet, hey 'if a little is good more must be better" jetting. But like Tnc we all seem to end up with different mods and stuff. I even remember debating whether the kdx snorkle should face forward or backward, LOL

I can truly say my main isn't too rich because I jetted in steps downward until it coughed, than went back to the next size up. On the A/F sniffer i should have gone 2 steps up. But I'm after run quality weighed against fuel range. So I'll leave that last little fraction of hp in the jet parts case for now.

The midrange? I tried a few different needles and they all burned the plug rich. the stock needle makes the plug look the nicest even with a kdx snorkle and screen removal.

Agree with the stock snorkle 120 is probably about right. A 120 can pull just as much fuel through the nozzle as a 128 with a little choke effect of the tighter airbox. Might explore the stock snorkle some more. Have a simple airbox design program I can run the inlets sizing, it is suprising how small it can be.

TNC the ping on wfo youmention was one of the symptoms of my slide lifting too fast with a drilled hole on my 650 when I went back to the stock needle on it for a high alt trip. Think thats why they HAVE to go with a steeper taper needle when they tell you to drill the slide? and decel popping from the slide dropping faster when you let off , they have you richen the pilot circuit more than usually is needed.