Jump to content

Recommended Posts

Hey guys

I just bought an FMF power core 4 and installed it on my 2012 250x, I wasn't sure when i bought but will this have to be re jetted for sure? I have never installed a aftermarket pipe before so i'm not really sure what mods need to be done, i know my way around an engine pretty well but not really sure about the re jetting. Any help would be great. 

Thanks

Share this post


Link to post
Share on other sites

In stock form the CRF250X is pretty choked up with it's enclosed airbox/small intake snorkel, restrictive muffler and lean carburetor settings.

If not already done, a common mod is to either drill some holes or partially cut out the top of the airbox and re-jet richer, especially the main jet.

 

Adding an aftermarket exhaust with the rest of the bike left in stock for would probably net lower performance and the engine running even leaner/hotter.

There is a CRF250X specific sub-forum in the Make/Model section where you'll get answers for most of your current and probably future technical questions.

Edited by mlatour
  • Like 1

Share this post


Link to post
Share on other sites

The smog assy (the PAIR valve I think is the correct term) doesn't affect power at all,

it simply introduces fresh air into the exhaust system during deceleration to complete the burn of extra fuel going thru the engine.

 

Removing it gains no power and doesn't require re-jetting but more importantly saves you about 1.5lbs worth of hose & clutter on the bike.

 

I've kept mods simple on mine, three 1" holes in the airbox, increased the main jet by 2 sizes (#130 to #135)

my latest mod is actually to tame down the engine for technical terrain: a 12oz heavier flywheel.

Edited by mlatour
  • Like 1

Share this post


Link to post
Share on other sites

Thanks guys for the quick info... I am ordering a JD Jet kit now and then gonna go from there. I knew that it needed to be rejetted anyway before the new pipe lol but just regretting having to do it. 

Share this post


Link to post
Share on other sites

Did going to fmf's site and looking under jetting cross your mind?  

17 minutes ago, Guly12 said:

Thanks guys for the quick info... I am ordering a JD Jet kit now and then gonna go from there. I knew that it needed to be rejetted anyway before the new pipe lol but just regretting having to do it. 

 

Share this post


Link to post
Share on other sites
5 hours ago, ossagp said:

Did going to fmf 's site and looking under jetting cross your mind?  

 

Explain what you mean by this? I went to their site and they don't have for the 250x

Share this post


Link to post
Share on other sites

Then it DID cross your mind.   Good work.  They seem to be shy when something is for a green stickered bike in printing things I guess.  If you bought a  pipe intended for a crf250 I would bet they start you there.  My experience using one of the eariler crfx cams is that they hold more vacuum and therefore live on slightly leaner jetting.  I am betting that if you call them and explain yours is close circuit use anyway that they would talk to you.  

Share this post


Link to post
Share on other sites
19 minutes ago, ossagp said:

Then it DID cross your mind.   Good work.  They seem to be shy when something is for a green stickered bike in printing things I guess.  If you bought a  pipe intended for a crf250 I would bet they start you there.  My experience using one of the eariler crfx cams is that they hold more vacuum and therefore live on slightly leaner jetting.  I am betting that if you call them and explain yours is close circuit use anyway that they would talk to you.  

Ok thanks for the info. I got a buddy who has done carb jets before so he is going to show me the ropes 

  • Like 1

Share this post


Link to post
Share on other sites

baseline for me is to set the float and record what  you set it to.   as it rises your jetting changes and it is just easier to set it back to factory each time you feel the need.  if your new pipe did not need anything to run it's best right where the stocker was you can kind of imagine that it didn't gain much,  so if you look for the silver lining you should want one that needs all the circuits changed!  

Share this post


Link to post
Share on other sites
12 hours ago, ossagp said:

baseline for me is to set the float and record what  you set it to.   as it rises your jetting changes and it is just easier to set it back to factory each time you feel the need.  if your new pipe did not need anything to run it's best right where the stocker was you can kind of imagine that it didn't gain much,  so if you look for the silver lining you should want one that needs all the circuits changed!  

Well when I give it gas right now it backfires and will stall out when you give it a little gas. So I assume that would be a sign it needs rejetting correct?

Share this post


Link to post
Share on other sites
3 minutes ago, Krannie McKranface said:

Just uncorking and changing the pipe would not cause this

You have other problems.

How did it run before you started.

It ran fine before changing the pipe but now it does backfire and stall/bog out in neutral when you give it gas . Don't forget how different the 250x trail pipe is compared to a "closed course" fmf pipe. 

Edited by Guly12
  • Like 1

Share this post


Link to post
Share on other sites
2 hours ago, Guly12 said:

It ran fine before changing the pipe but now it does backfire and stall/bog out in neutral when you give it gas . Don't forget how different the 250x trail pipe is compared to a "closed course" fmf pipe. 

Exactly.   If you don know what your current jetting is,  I would be inclined to find out what was in it at least as far as the pilot jet goes.  Compare that to what FMF suggests for the crf with the same pipe.  Again,  if the stock crfx cam is in your rig,  it will hold more vacuum than a crf cam will.   You may be able to make yourself happy with some fuel screw adjustments.  Popping can sometimes be something like a leak,  but the stalling is not something I ever get with a pipe installation that leaks.  Did you do anything else,  or modify the intake since it worked well? 

  • Like 1

Share this post


Link to post
Share on other sites
44 minutes ago, ossagp said:

Exactly.   If you don know what your current jetting is,  I would be inclined to find out what was in it at least as far as the pilot jet goes.  Compare that to what FMF suggests for the crf with the same pipe.  Again,  if the stock crfx cam is in your rig,  it will hold more vacuum than a crf cam will.   You may be able to make yourself happy with some fuel screw adjustments.  Popping can sometimes be something like a leak,  but the stalling is not something I ever get with a pipe installation that leaks.  Did you do anything else,  or modify the intake since it worked well? 

No I have not done any air box mods or mess with the carb at all. Everything there is stock.. only thing new would be the muffler 

  • Like 1

Share this post


Link to post
Share on other sites

Then the jet sizes should come right out of the manual.   I think my first shot if your pilot jet is within two sizes of what fmf suggests for that pipe on a crf250 would be the fuel screw.  The stock one on my crf is a bitch to get at.   They sell some nice ones that are not so challenging to use to adjust.   

Edited by ossagp
  • Like 1

Share this post


Link to post
Share on other sites
8 minutes ago, ossagp said:

Then the jet sizes should come right out of the manual.   I think my first shot if your pilot jet is within two sizes of what fmf suggests for that pipe on a crf250 would be the fuel screw.  The stock one on my crf is a bitch to get at.   They sell some nice ones that are not so challenging to use to adjust.   

Ok I will look into it. I might put the JD jetting kit in anyway because I know a few guys who put it in their 250x and they love it 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×