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2008 250X sputter/bog

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Hi all,

 

my name is Matt, I've come across heaps of topics from here in the past when searching for stuff so I thought I'd register and become part of the community ūüôā.

 

I live over in the Mid North Coast of NSW in Australia. I had an 08 250R a few years ago which was a great bike, and have now recently purchased a 250X to get back into riding. My riding consists of mostly trails and the occasional farm or field.

 

The first few rides a went on the bike performed smoothly, however it has recently developed a bog or 'sputter' once it is at full operating temp. From what I've read on here and seen a lot of YouTube videos it is a different kind of bog to the 'famous' FCR carb or CRF bog. If the RPMs are anywhere below 5-5.5k and I give it over half throttle or so it will sputter and carry on, best described as if you were running out of fuel when you're trying to ride. Once the RPMs are over 5k or so it will clear up and pull hard. If I ease on the throttle there is no issue. It happens in every gear and is most noticeable once I've been riding for 15-20 mins.

 

Mods when I got the bike:

 

Opened airbox

DEP exhaust

Previous owner said the owner before him had the cam done but I'm not sure how to check this.

40 pilot jet

170 main

 

Since I've owned it I changed the pilot to a 45 and fitted an after market fuel screw and set it at 1.25 turns which makes the bike a lot more responsive, until it starts playing up.

 

I'm unsure of the leak jet size as one of the screws holding the bowl on has been rounded, so I'll most probably have to pull the carb and fix that before I change the jet. I will check the AP squirt once I sort the jetting, a 50 leak should do from what I've read.

 

Sorry for the long post, I tried to explain it my best! I could probably get a video of it if it'll help understand what I mean, just let me know.

 

If anyone has any idea or recommendations that would be great, I've not been able to find anyone with the same kind of issue.

 

Cheers!

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I don't think it's your AP. If it's only sputtering when it warms up, you're likely too rich. I would decrease the size of your main. If you're near sea level (less than 3,000 ft I believe) your pilot is a bit small and should be changed to a 42. Better yet, get a JD jetting kit for $76 and be done with it. The fuel screw setting on the X should be closer to 2 or 2-1/4 turns so you may have something else going on like an improperly set float level. Set it to 8mm.

JDH003 jetting kit: https://www.jdjetting.com/xcart/product.php?productid=3

Edited by mossman77

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Hard to say if it's the AP or not from your description.   If your snapping the throtle open, then that would be AP.   But if your rolling it on or holding steady, then that is main, and/or needle, and/or clip position.

 

As for the slow jet, that does contribute a little bit as well, so first thing I do is get that squared away.  You didn't mention altitude, but like mossman, a #45 is probably too big.     On a fully warmed up motor:

 

1. Lower the idle to just running.

2. Turn the fuel screw for the smoothest running.

3. Repeat until you can't keep the bike running.

4. If you get a hanging idle (idles high and then drops after about five seconds after closing the throttle), go 1/4 turn out.

 

5. If you end up at <1 turn, then the slow jet is too big.   If more than 2 1/4 or so, then it's too small.

 

Try this with your #45 first.   You are opened up pretty well so you might be OK, but it would be better if you were more like 1 3/4 - 2 turns out.  Normally, the 250 takes a #42 at sea level.

 

Once you have the slow circuit sorted out, then move on to main, needle, and clip.  Carb tuning is done top down, so start at WOT first.   Should run clean.    Next you'd want to play with the needle (if at all), and then clip position.   There is a FAQ on jetting at the start of the forum where a lot of people list their setups.   This is what is in use at what throttle  position (and note it's throttle position that's critical, not what the motor is doing, so mark off your throttle with tape).

 

Keihin <a href='https://thumpertalk.com/link/click/4794/' rel='nofollow' data-ipsHover-target='https://thumpertalk.com/index.php?app=autolink&module=links&controller=content&id=4794' data-ipsHover target='_blank' rel='noopener' data-autoLink>FCR Carb</a> Tuning Components.jpg
 
 
Enjoy the X!
 
Jim.
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Thanks for the replies guys, I'll have a play around and get back to you. Cheers!

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I highly recommend getting a JD kit. Install the jets and needle and you're done. Quick and simple, no guess work.

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You never mentioned if you changed the needle. Could be the NCVS (is that even right?) Needle would help. How old is the bike. Maybe look at replacing the needle jet as well.

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Yeah I will grab a JD kit, only reason I haven't yet is I had jets from my old R that I thought I'd test, however the only one of use was the 45 pilot.

My altitude is 26m (or 86ft), does the JD kit come with recommendations regarding altitude? That way I can just install it all at once and hopefully not have to play around with it too much more.

Thanks for the help so far, much appreciated.

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Yes, the JD kit tells you which needle to use (kit comes with two), and which pilot and main. Don't remember if it comes with a needle jet. I want to say no. Go to their website and look at the details for the JDH 003 kit. If not, it may be a good idea to pick up a new needle jet. If yours is nicked, scratched, etc then it will cause issues. I would also get a complete gasket kit and a floating seal. These are known to go bad over time and cause a lean mixture. So:

JDH 003 jetting kit, OEM needle jet, OEM floating seal, OEM gasket kit. Total cost about $150. You should be running right after this.

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A couple other things, clean the carb passages with carb spray followed by compressed air. Do not soak the carb. Set the fuel screw to about 2-1/4 turns to begin with, then fine tune once you have the bike warmed up and at the proper idle. And assuming the TPS hasn't been screwed with, a good way to set a basepoint for the idle screw is to measure the TPS resistance while adjusting the idle screw until you get a reading of about 650 to 750 ohms. If you're fuel screw and idle screw aren't ballpark then you'll have a very difficult time starting the bike. Good luck.

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JD kit comes with a slow jet (#42), two needles (blue one for below 60 and red one for above), and a handful of mains.  It does not come with a new emulsion tube (what the needle rides in).   Note there is nothing magical about a JD kit.   It does come with a multi-taper needle that you can't get anywhere else, but you can get a well running bike without it.   Where teh JD kit really shines is the knowledge that comes with it; for this temp and altitude, install this main, needle, and use this clip position.   It gets you pretty well set right away (you still can tune some more, but most are pretty happy with the setup right off).

 

With a mid-range bog, I would not think a new slide seal would be in order, but it may be worn and contributing to you needing a #45 slow jet.   If anything, I would order the emulsion tube.   On a bike this old, chances are it's started to oval and is letting fuel by the needle.  This would show up mostly in the mid-range and your description of the problem said that it ran well initially and that this problem developed over time.  That sounds like wear or something getting plugged up.

 

Also if your going to use carb clearner, the carb needs to be throughly dis-assembled and all plastic and rubber parts removed (anything that is solvent based will destroy those).   Brake cleaner is a better choice (it's safe) and I've heard Pine-Sol (common household cleaner) works really well, but I've never tried that myself.

 

Last, fishing line or guitar strings work very well for cleaning small passages.  Cleaner and compressed air don't always do the job, especially on the one passage between the fuel screw and the slow jet cavity.

 

Jim.

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Floating valve seal is only $15 on CRFsOnly, so might as well replace it for good measure.

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Will get those parts ordered and post the results when I've got it all back together.

Apart from that it's been great to get back onto the trails!

Thanks again guys.

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Hey guys just a quick update.

Installed a JD kit, floating valve seal and emulsion tube. Went for a ride over the weekend and the bike feels pretty good. Hopefully it's all sorted now!

I found that Honda don't sell the seal separate, only the complete assembly which was in excess of $220 AUD. Thankfully Yamaha sell the seal separate. I would have gone with the CRFs Only seal but once postage and currency conversion worked out it would have been more expensive.

Anyway thanks for the help, happy riding ‚ėļ

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