Jump to content
Sign in to follow this  

jetting and needle positions with aftermarket exhaust

Recommended Posts

I been having an issue with my 2009 YZ250F. I cant seem to get my settings right and get rid of my unresponsive throttle. I have a complete FMF exhaust ( mega bomb with Q4 slip on), I have added a boyseen quick start to  my bike and put a MSR quick adjust for my air fuel screw. I put in new main and pilot jets. running one size bigger than stock (72 main and I believe it was a 48 pilot). raised my needle 1 setting up (Yamaha shop recommended it). so my settings for all of that as of right now are straight from the dealership. 1 size up on both jets, 1 click up on needle, quick start set at 2 turns out, air/ fuel set at 1.5 turns out. with that my throttle still hesitates when I snap it from idle. any suggestions on how to fix this.

Share this post


Link to post
Share on other sites

Most of the information is just plain wrong

Jetting has nothing to do with quick WOT 

That's the accelerator pump system.

Oh, and if you are testing this in neutral on the stand, ignore that, as it means nothing. You must have load on the motor to test quick throttle action.

 

170 main

45 pilot

NCVS needle on 3rd clip

50 leak 

...and service your accelerator pump system, which is what gives your throttle response.

GET RID OF THE BOYESEN and put in a 2008 upgrade kit instead:  http://www.crfsonly.com/catalog/product_info.php/cPath/138_147/products_id/3932

 

Then get a R&D remote fuel screw, and PROPERLY adjust the fuel screw to get max idle speed.

Edited by TheKoolAidMadeMeSick
  • Like 2

Share this post


Link to post
Share on other sites

The stock pilot is 42. Ive also been told that 2009 yz250f are usually lean off the bowl. Try a 45 pilot jet

Share this post


Link to post
Share on other sites

Can the CRF pump be used on a 2007 WR 250? I was considering a Boyesen Quickshot 3.

The Boyeseen doesn't work; it's just an adjustable leak jet and does not solve the bob problem

 

The FCR carb is used on several dozen different bikes

The Honda influence gets them to get Keihin to provide them with 'better' versions of the carb.

Share this post


Link to post
Share on other sites

The Boyeseen doesn't work; it's just an adjustable leak jet and does not solve the bob problem

 

The FCR carb is used on several dozen different bikes

The Honda influence gets them to get Keihin to provide them with 'better' versions of the carb.

So will the CRF kit work on an 07' WR FCR? What exactly is the best accelerator pump setup? My WR has the stock timing but o-ringed. My GYTR jet kit came w/ a 90 leak that actually feels better than the 60 the local moto shop recommended.

Share this post


Link to post
Share on other sites

Yes

The Last version offered by Keihin/ the one listed is the best stock version

The R&D powerbowl-2 is the absolute best
You have to visually tune your squirt for 1 second, and just barely missing the slide. Adjust timing using the apump linkage screw.

  • Like 1

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:

Sign in to follow this  

×