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Old December 11th, 2008, 11:00 PM   #1
VeX
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Lightbulb DIY - Changing jets WITHOUT removing the carburetors

Considering tuning type stuff such as re-jetting involves experimenting with 3-4 jet changes I find it silly to have to remove the carburetors every time. Someone on another forum did a step-by-step on how to accomplish this, and I snapped pictures (although he never USED the pictures )

Jetting a carburetor can be considered step 1 in carburetor tuning! It is critical that you find the right jet size before you move onto fine tuning the needle height. A quick range of jet sizes for the '08+ 250r is as follows:

.................. Keihin/Factory Pro ........... Dynojet
With airbox........98 - 102......................96 - 100
NO airbox..........108 - 115 ...................104 - 110
The process is the same for each carburetor so I'll just go over one:

Step 1: Remove the front fairings. Go ahead! Take those bad boys off. You can leave the fuel tank and seat and everything else put...

Step 2: Hook up a section 2'-3' long to the drain on the fuel bowl:

The hose ID is 3/16" or 1/4". Both will fit over the drain port. Also circled in the picture is the allen screw to open the fuel bowl drain.


There's not much fuel in the bowls so I just used a cap to a can of bondo to pour the fuel into. Don't worry about the fuel petcock or anything. With the vacuum operation on these engines the petcock remains closed as long as there is no vacuum present (ie. the engine is off).

Step 3: Remove the fuel bowl.
I assure you this tool is going to get brought up in a lot of these DIY's, so do yourself a favor and buy one... DO it! (Milwaukee Offset Screwdriver with a ratcheting screwdriver handle)

While the screws from the factory are phillips head screws, Factory Pro includes new allen head screws. So be careful taking the stock screws out as it is possible to strip those suckers.


There are a total of 4 perimeter screws holding each fuel bowl on. Make sure it's one of the 4 screws that hold the fuel bowl on. There is an extra screw down there that is NOT one of them.

Step 4: Remove the jet!
If you did step 3 correctly and drained the fuel bowls, the fuel bowl should drop without any noticeable fuel leakage.

Circled in red on the left is the main jet... Yup no voodoo or searching, it's right there... You have to hold the jet extension tube though while you unscrew the jet so:

Hold the jet extension tube with a boxed wrench and again (with the Milwaukee Offset Screwdriver) throw a flat blade bit on and it should unscrew easily!

... That's it! Put the new jet in and lightly tighten it. I'm not going to list torque specs, but if I DID it'd be in inch/lbs. Toss everything back together (minus the fairings) and warm the engine up.

After a brief ride around test the performance from around 8,000 RPM to red-line. If the bike pulls harder then previously then try bumping up one more jet size. Keep doing this until you feel you've lost a bit of top end power. Then drop to the jet size below that and you've completed step 1 of carburetor tuning!

Last futzed with by VeX; January 7th, 2009 at 01:40 AM. Reason: Re-directing URL's
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Old December 11th, 2008, 11:13 PM   #2
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Thanks!
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Old December 11th, 2008, 11:16 PM   #3
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Good job!!! I like it!! Though, cracking that main jet loose is a bitch. I had a hard enough time with the carbs out doing that, I can imagine how hard it might be with the MOS. The slot for the common blade was a difficult thing to find one that wouldn't mar the jet. Also, as you said, you need to hold that tube the main jet is screwed into with a wrench to prevent it from unscrewing from the carb body.

some additional carb pics for those that would like to get familiar with the carbs if you are thinking of doing this. My pictures are with the carbs off the bike, but you can use them to familiarize yourself of what it looks like inside the carb.

http://picasaweb.google.com/kkim993/AirboxAndRejet#
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Old December 11th, 2008, 11:47 PM   #4
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Thanks Kelly. Those pics give me some confidence.

The pictures regarding the FP needle I see you have washers. It's kinda hard to see but on the needle is it: e-clip, washer, washer, then e-clip?
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Old December 12th, 2008, 12:01 AM   #5
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wow that didnt look so bad.

Thanks Vex!!
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Old December 12th, 2008, 12:07 AM   #6
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Quote:
Originally Posted by islanderman7 View Post
It's kinda hard to see but on the needle is it: e-clip, washer, washer, then e-clip?
yes, that's what I have. Read your instructions that came with the kit... they recommend you put the washers in.

in this pic, you can see the clip clearly on the 3rd (middle ) notch.




in this pic, the clip in the 3rd with 2 washers above the clip and I added another clip above the washers to keep everything from running away or falling off. All that really matters is the clip in the 3rd notch. The 2 washers and other clip are there to stabilize the needle in the carb to keep it from dancing around.

Here are the FP needles with clips and washers alongside the stock needles.

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Old July 14th, 2009, 06:51 PM   #7
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I'm about to install a jet kit on my bike and would like to use this method... but, is there any way to get the caps off of the idle mixture screws while leaving the carbs in the bike?

I'm just trying to estimate my work before I start and realize that this cant be done.
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Old July 14th, 2009, 09:06 PM   #8
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Quote:
Originally Posted by NJD022588 View Post
I'm about to install a jet kit on my bike and would like to use this method... but, is there any way to get the caps off of the idle mixture screws while leaving the carbs in the bike?

I'm just trying to estimate my work before I start and realize that this cant be done.
VeX used Milwaukee Offset Screwdriver to get his out check out his DIY - Accessing and adjusting idle mixture screws http://www.ninjette.org/forums/showthread.php?t=10246
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Old July 15th, 2009, 06:03 AM   #9
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Thanks a lot! I didnt even see that DIY. I already have the Milwaukee Offset Screwdriver so this problem is solved before it ever became a problem.
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Old May 16th, 2011, 06:37 PM   #10
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Sorry to revive the old thread but does anybody have any experience removing the jet extension tube? I removed mine when I rejetted and Im curious if theres any potential issues with doing so. PN #16017: JET-NEEDLE,#6 sits on top of the jet extension tube and I put it back in the same way it came out but it didnt look like it actually seated itself or screwed into anything. Just wanna double check my work. Thanks!
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Old May 24th, 2011, 05:01 PM   #11
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Could you just take the jet extension part out with the jet and then change it out of the carbs? Seems like it would be easier. I did this method last night and getting just the jet out with the MOS was a b*tch
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Old May 25th, 2011, 07:08 AM   #12
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Quote:
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Could you just take the jet extension part out with the jet and then change it out of the carbs? Seems like it would be easier. I did this method last night and getting just the jet out with the MOS was a b*tch
Thats what I did and I haven't had any issues. Just make sure you keep track of that tiny jet that sits on top of the extension tube.
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Old June 14th, 2011, 02:12 PM   #13
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Speaking of that little jet that sits on top of the extension tube (the jet needle), do you happen to know which way it's properly oriented? I think it's with the smaller hole facing 'down' towards the extension tube and the larger hole facing 'up' toward the needle jet and the diaphragm slider.

Edit: Checked the FSM. It says to insert the end with the smaller diameter facing 'up' once the carb is oriented as it would be on the bike. As such, my assumption above is correct. Also, it doesn't fit properly the other way
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Old June 29th, 2011, 11:17 PM   #14
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Do I understand correctly that I can only get to the main jets with this method, but it won't work for getting to the pilot jets?
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Old June 30th, 2011, 08:46 AM   #15
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Quote:
Originally Posted by MysterioX View Post
Do I understand correctly that I can only get to the main jets with this method, but it won't work for getting to the pilot jets?
Are you talking about the pilot jets or mixture screws?
The mix screws can be adjusted with this method/tool (the Milwaukee Offset Screwdriver) very easily, with the right flat-head bit.

Swapping pilot jets can can be done without pulling the carbs. I did it, but you need a narrow-shafted, relatively wide bladed flat-head screwdriver that's no more than about 3" long including the handle. The usual multi-head screwdriver bits (hex-shaped base) are too wide to fit in the hole, so you can't use those or the MOS, unless you've got one with a blade shaft that's about an inch long (never seen one). Also you'll want fairly small hands, that can get in under the carbs to get torque on the screwdriver. I imagine it could be done with a pair of vicegrips on the screwdriver, but I didn't have to try. In short, it's doable, but you need to have a screwdriver of just the right proportions.

I realize this may be confusing but it's the best I can think of explain without pics, which I didn't think to take when I did my pilot swap about a year ago.
Here's the screwdriver I used, Craftsman 4-in-1 #45734. I got to the pilot jet with the wide-blade flat bit with the black extension, but not the handle.
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Old June 30th, 2011, 10:47 AM   #16
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why do you think you need to change the pilot jets?
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Old June 30th, 2011, 12:11 PM   #17
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Quote:
Originally Posted by Momaru View Post
Are you talking about the pilot jets or mixture screws?
I'm talking about pilot jets.
Thanks, I'll look into getting appropriate screwdriver.
I was thinking this tool to take the carb bowls and just get an extension for it to get to the pilot jets.

Quote:
Originally Posted by kkim View Post
why do you think you need to change the pilot jets?
My bike was sitting for a while and I have a strong suspicion that the jets need to be cleaned. I put some seafoam into the tank for now, but if that doesn't work, I'm onto the carbs.

Would it work if I just got a carb cleaner and using a small plastic tube sprayed the cleaner directly into the jets without removing them?
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Old June 30th, 2011, 10:19 PM   #18
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Originally Posted by MysterioX View Post
Would it work if I just got a carb cleaner and using a small plastic tube sprayed the cleaner directly into the jets without removing them?
I'm sure there's other screwdrivers that'll work, that's just what I happened to have on hand that fit the bill for the job.

If you're looking at clogged jets, I'd think long & hard about just pulling the carbs & giving them a proper cleaning. There's lots of little passages in the carb body that may also be clogged; pulling the jets won't get them. An air compressor is your best friend for that kind of job.

From my experience, the carb cleaner won't clear the kinda gunk that builds up in our carbs (or mine at least). I pulled my pilots and soaked them in the stuff for half an hour with no appreciable change when I had that problem earlier this year. Does great for cleaning off the standard road crud though.

And I've got one of those lateral screwdrivers. Bought it for the same job. I didn't have much luck because I couldn't get enough pressure at the right angle on it to keep from chewing up the screws.

Both ideas are worth a go though, you may have better luck with them. Only thing you're likely to lose is a little money on tools/cleaners that are handy to have anyway and some time trying to do the jobs the 'easy way' before trying it the 'hard way'
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Old June 30th, 2011, 10:45 PM   #19
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John... as Paul stated, it's best to pull the carbs to give it a thorough cleaning. Once I remove the jets, I always like to "back flush" the passages if I suspect something is clogged. use compressed air in the opposite direction that the fuel/air flows though the passages.

You've got nothing to lose trying it your way, but I'd be surprised if it worked. let us know if you succeed.


btw, have you seen this DIY on pulling out the carbs?

http://www.kawiforums.com/ninja-250r...ll-re-jet.html
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Old November 2nd, 2011, 07:47 AM   #20
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So if you change up your exhaust and want to do some rejeting to ensure that the mixture doesn't become even more lean then stock, all you have to do is change the main jet? If im not mistaken, the dynojet kits sold for rejeting the ninja 250r are a state 2 kit. Is this considered overkill for just swapped out exhaust? I would really like to do the rejeting myself but don't want to mess with taking out the whole carb, so if i can just do it using this process that would be nice. Otherwise im just going to take the bike to my local shop and have them instal the whole stage 2 kit.
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Old November 3rd, 2011, 05:14 PM   #21
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Different jets focus on different sections of the power/throttle band. If you're just throwing on a slip-on exhaust, you can probably get away with very little rejetting because you'll see very little benefit other than a change in how the bike sounds. If you're doing a full system exhaust replacement, you'll want to retune your pilot screws (no new parts needed), your needles (adjustable with washers of the right size if you don't wanna buy the kit) and the mains (can be purchased individually for ~$2/jet).

Technically speaking, you can get all the jet tuning done without pulling the carb. But adjusting the needles will require pulling the gas tank.

There's a bunch of threads on the forum for tuning etc, might try the 'jetting database' for a start
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Old May 29th, 2012, 01:32 PM   #22
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Has anyone used JIS bits for the screwdriver or is there any problem using the american ones?
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Old May 29th, 2012, 04:39 PM   #23
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You can but you have to be really careful as they are easy to strip.
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