How-To: KX250F Jetting Specs
Year, Make, Model
2006 Kawasaki KX250F
Jetting Specs
I am going to list stock, as received, and the final jetting specs I ended up with.
Stock:
Leak Jet: 60
Main Jet: 180
Needle: NCYU – 2nd groove from top
Pilot Jet: 40
Fuel Screw: 2 ⅛ out
Float Height: 8±1mm
No o-ring mod
AP timing: stock
As recieved:
Leak Jet: 55
Main Jet: 175
Needle: NCYU – 5th groove from top
Pilot Jet: 45
Fuel Screw: 3 1/2 out
Float Height: 8±1mm
No o-ring mod
AP timing: CCW until screw was about to fall out
Final Jetting:
Leak Jet: 45
Main Jet: 175
Needle: NCYU – 3th groove from top
Pilot Jet: 45
Fuel Screw: 2-2.5 out
Float Height: 8±1mm
O-ring mod
AP timing: 3.5 turns CCW from stock (squirt just misses the slide)
How-To Video
I have a detailed post here on How-To jet a 4 stroke carburetor. It covers everything you need to eliminate that bog and get that front wheel off the ground!
Other KX250F How-To’s
Here is a post/videos on a full top & bottom engine rebuild.
Here is a video on valve adjustment.
Comments
Has this information helped you? Please comment below.
Hi Matthew, would the final jetting sizes you determined for the KXF250F in your video suit my 2005 CRF250R, as I believe both bikes have the same carb?
Pete, the jetting sizes for pilot jet and leak jet will be very similar. Overall, this is a guide since all bikes usually have different modifications and are ridden in different climates.
Are you trying to solve a specific issue on your bike?
Where can I order these jets through you?
Nathan,
I don’t sell any parts, however recommend RM ATV as a good source. Here is a post with the exact jet styles needed:
http://www.howtomotorcyclerepair.com/jeta4stroke/
Hi Matthew I have a rmz250 04 (the bike isn’t running) and the bike back fired when I downshift or let off the throttle, when had it running Whitch means lean right? But when I go to kick start it now it doesn’t start but back fires with every other 5 or so kicks,loud pops to! So that means rich? Sparke plug is black lol and I haven’t yet checked the needle clip? Should I put the clip up to lean it more or should I put the clip on the needle down to make it rich more thanks please help:)
Tommee,
Get it running and check for vacuum and exhaust leaks. Then pull the carb and clean it. Make sure to write all jetting down and compare to stock. Get back to me when you have the carb apart.
https://howtomotorcyclerepair.com/how-to-diagnose-motorcycle-vaccum-leaks/
https://howtomotorcyclerepair.com/4strokecarbclean/
Matt
Thanks for the fast reply:) the thing is I can’t get it started? And sometimes when I do get it going…I have to keep the throttle on a little to keep it running? But stays running with choke on Whitch is good, but I just don’t understand what the problem is! I’ve cleaned and cleaned the carb also, the only thing I can think of is timing but it also looks good, maybe I have the wrong jets in the carb? Ps on the needle the clip is all the way down on the last clip..that explains the pops when kicking (flooding)
Sounds like a pilot circuit problem. Did you remove fuel screw and pilot jet and make absolutely certain the pilot jet and all passages are clean? Spray carb clean and blow them out with compressed air. Verify pilot jet size and compare to stock.
If it only runs on choke, then the pilot circuit is not supplying enough fuel. It’s either dirty or set up too lean.
I removed all parts and jets, cleaned with carb cleaner and I have a fuel screw mod so I set that to 1 and a half turns out, (stock) ok so how do I find the pilot jet size? And if the bike pops with every 5 or so kicks isn’t it set up rich? Thanks for your time👍
Do you have the service manual? If not, buy one since it will have all the info in there. I looked up in the parts diagragm and stock pilot is #40. I usually set these bikes up with 1-2 larger than stock. Basically keep increasing pilot jet size until fuel screw wants to be at 2 turns out for peak RPM during adjustment. Does it backfire out carb or exhaust?
No but I have a online service manual with everything in, so yeah I do have one. So will the jet have the size on it so I can check what size?? And back fires from exhaust, confusing because backfiring when riding is lean BUT backfiring when kicking means rich? So I’ll mess around with the pilot jet size, but where do I put the needle clip then? In the middle (best of both worlds?)
Yes, jets are stamped with numbers. Not sure what all the backfiring is about, however you need to take that carb apart and see what is going on.
Matt
hello sir. my 08 kx250f is having trouble with low end bogging and backfiring. and hanging idle. i just fixed the valve clearance. before i did that the intake clearance was .000 which is bad so i fixed that not its having issues. should i start with the fuel screw first or go straight to rebuilding the carb with the different jets?
I would recommend that you pull the carb and clean it. While apart, write down all jetting and compare to what I posted.
Here is a carb clean video if you need it:
https://howtomotorcyclerepair.com/4strokecarbclean/
Matt
https://uploads.disquscdn.com/images/7ca7357754c36401ec6fb7acba188d222bcc1776e96ff91156f43b76d2fa2b52.jpg
main is 162. can’t read it on the picture. everything is clean. moved the needle on click up. ill fire it today to see what happens
I would recommend a smaller leak jet, like a 45. Also, buy a 45 pilot (just in case) and adjustable fuel screw. Did you check the condition of accelerator pump diaphragm?
Hi matt, i owned a classic 250cc bike, just replaced my stock carb from 28mm to 30mm roundslide. Stock jets from 30mm is 42 slowjet and 152 mainjet. When i tried it on the road, my bike is backfiring when im hitting the 4th gear on 5k to 6k rpm, then the engine stall. So, i replaced the main jet to 120 and it resolves the backfiring on 4th gear. Now, my problem i find my idle unstable, its like im running like a car with an aircon ON. I need help to resolve my problem and how to find the right jets for my bike.
Thanks!
Ralph
What year make model? What kind of carb? Air or fuel screw?
I am using a 30mm kehin pe roundslide carb. Air screw is what on the carb. Im on 2turns on idle screw
Do you mean 2 turns on air screw? Is the air screw responsive at 2 turns out?
Yes. But i have uneven idle speed. It idles fast then slow a bit and sometimes it stalls
Did you check for vacuum leaks?
How will i know if there is a leak?
Leak jet? You can look it up in the parts diagram or pull the fuel bowl.
Is this for low elevation? I just picked up an 09 and I’m going to get into. Looks like you have your dialed. I’m low elevation Ontario Canada. So curious if your set up would work.
I’m in Chicago. 700′.
Matt can you elaborate also on the o ring mod. Is it possible to forward answer to my email? I think the carbs are pretty close. I believe my 09 comes with the tapered needle.
Read this: https://howtomotorcyclerepair.com/jeta4stroke/
Hey Matt! So I have a 2008 kx250f that I picked up that will idle all day long but won’t take any throttle whatsoever. My leak is a 55, Main is a 175, Needle is the NCYU 3rd from the top, Pilot is a 40, Fuel Screw is only half a turn out to get max rpm, It has the O-ring mod as well sitting about 3.5 turns out. I’ve been in and out of the carb a dozen times already and can’t seem to figure it out. Any suggestions?
1/2 turn out on fuel screw with 40 pilot jet is not right. That is a super lean setup. What happens when you start to turn it out to 2 or 2.5 out?
Where are you located? Elevation?
When I begin to turn it out the idle decreases and will eventually kill it. I am located in Kansas with an elevation near 2700 ft.
OK. Is this a new problem or has it always been this way. Can you email me a video?
It’s a new problem and yes I could email you a video of it running
What is the email I need to contact?
https://howtomotorcyclerepair.com/contact/
Hello Matthew, I have a 07 kx250f and i am having same issue with throttle. When you crack it fast it falls on its face. I put same jetting that you did in the suzuki and messed with the accelerator pump, i also replaced pump and still doing same thing. i have taken it in couple times for issue and have not been able to get it fixed. any suggestions?
Did you go larger on pilot jet?
Fuel screw 2-2.5 out?
Leak jet 45?
Oring mod?
Acc pump timed good?
The only thing i havent changed is the leak jet. I think it has a 55. I adjusted it and still nothing
Turn the choke on and see if problem goes away. If it does, it wants more fuel. I’d go 45 on the leak jet IMHO.
Hello Matthew,
So i went 45 on leak jet and it was worse. It died when i gave it throttle.. but does run good with choke on
OK, so it wants more fuel.
1. What pilot jet size?
2. Fuel screw setting? Tuned for peak idle RPM? Screw should be 2-2.5 out when all said and done.
3. AP squirt powerful and lasts about 1sec?\
4. Minimal play in AP timing linkage?
Matt
I will try that thank you
How close would this be for a 05 kx250f
Close enough, copy the specs and see how it runs.
Hi my 2004 kx250f is all stock I live in NY the bike is stock and jetting is 155 Main and 40 pilot valve clearance and everything is good carb is clean it is quite hard to start when the bike is warmed up and hard to start sometimes and does some loud backfires when trying to start but when it runs it runs strong but Idle Hands a little when I try to richening up the carb it runs worse and if l floods easily what should I do thanks also it will not start on choke only on regular
Have you tuned the fuel screw: https://howtomotorcyclerepair.com/how-to-4-stroke-mx-fuel-screw-adjustment-yzf-crf-kxf-rmz-fcr/
How many turns out?
Hi I have a 2010 kx250f and I can’t figure the jet sizes to put inside of the carb. The bike has stage 2 cams does anybody know the right size Jets to put inside my bike. and would you guys also know where to put my needle clip on the needle. Thanks
I don’t have exact specs for that combo.
I’m working on this 2007 kx250f I’ve changed the radiators because the right one had a leak & the left one was bent & the hoses, I’ve replaced the head gaskets because they were blown, I’ve replaced the water pump seals because the oil was kinda milky, ive replaced the valves & valve stem seals, I’ve reshimmed the valves to the proper clearance, I’ve rejetted the carb a few times frm stock to a 42 to a 45 back to stock & now back to 45 pilot 175 main I can’t remember what the leak jet is but I can’t get this bike to stay running off of choke to save my life & not to mention I’ve let the carb soak in the chem dip for 48hrs…. Do u have any suggestions at all?!
Did you let the entire carb body soak in chem dip? There is a mid body gasket that may have gotten ruined. Put a 45 pilot jet in with fuel screw 2.5 out for starters.
Yea I did & I have a 45 pilot jet in there now i even sprayed the the carburetor & intake boot w/carb fluid to checking for any leaks & frm what I can see there were none…
Wassup Matt I’m working on this 2005 kx250f the customer had the entire engine rebuilt & couldn’t get it started so I shimmed the valves & cleaned & rebuilt the entire carb it starts & runs fine his neutral switch was messed rite along with his flywheel we replaced both & he was missing the breather tub for the oil ordered that put it on & now every time I crack the throttle it shuts off but it ran perfectly fine before that I don’t understand what’s going on w/this bike & they don’t have no detailed videos on YouTube for this particular bike on the neutral switch do u have any suggestions?
Is the accelerator pump functioning properly?
Hi Matthew. My 2004 KX250F is VERY difficult to start cold. It has the correct jetting #42 pilot, #178 Main, #55 leak jet, and all others stock. Everything else that would cause this has been ruled out except carb issues. The only way I’ve been able to get it to start at all cold is to kick it while holding full throttle. Once it does start, it runs really good, idles good and has great throttle response. However, the fuel screw is out 3.5 turns at least and the idle speed screw is screwed in far more than normal to run right. Once hot, I have to hold the throttle at about half throttle to start without the choke on. Any ideas?
Make sure the carb is clean.
Next, adjust the fuel screw while running per this video:
https://howtomotorcyclerepair.com/how-to-4-stroke-mx-fuel-screw-adjustment-yzf-crf-kxf-rmz-fcr/