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fcr41mm to xr650r jetting

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Hi everyone,i have a 07 Crf450r 41mm carb and it came with a Pilot jet- #42 ,Pilot air- #100 ,Main jet- #178 ,Accelerator Pump Leak Jet- #50 and Needle - NJYR with clip in the #3 slot and I tried it on my xr650r. The bike fired up in one and i set the idle .Now when i rev the bike it bogs down bottom and then revs out fast. Can anyone give me a starting point on getting it tuned right?.My bike is uncorked ,stage1 hotcam with a 3 x 3 inch air box mod and a full big gun exhaust,the type that runs behind the radiators,and I ride from sea level to 500 ft and temperature is mainly about 23-27 degrees celcius here in Barbados .The oem carb works good but i want to experience the feel from a pumper after hearing of other members saying how great it is and the riding a crf450r. Can someone please chime in? Below pic is the set up of the AP linkage ,do i need to do any oring mods here?.Any and all input is welcomed and thanks in advance for your help

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45 pilot

NCVS needle 3rd

30-40 leak jet

Main jet: 165-178 range. All depends on your air density and pipes. If you are running non-stock headers, you need larger. If you are running non stock headers and a real muffler, larger still. 

....but the REAL issue is the apump system. That is the symptom you describe . You must upgrade to 2008 Honda specs for any real positive results.

The R&D Powerbowl-2 kit or these parts will get it right:

http://tokyomods.com...arburetion.html

  http://www.crfsonly....roducts_id/3932

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if i read correct the 07 and 08 crf450r carbs are the same. the only difference is the jet needle.the both have the same AP covers and linkages

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9 hours ago, fixy said:

if i read correct the 07 and 08 crf450r carbs are the same. the only difference is the jet needle.the both have the same AP covers and linkages

This can be true. If the carb in your pic is yours, that is the upgraded carb.

 

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I am running the full HRC kit (cam, piston, etc...) with the XR's Only LE race exhaust (large header & full megaphone can).

I am nominally at 4000ft/1200m and usually am riding at areas a lot higher.  When I get closer to sea level I typically go up one on the pilot and one on the main, if not 2.

My jetting:

45 pilot

100 air

188 main

NCVS needle (3rd from top)

I am using a Merge externally adjustable leak jet AP pump cover, it is typically set to around 1-3/4 turns out.  I am not sure what that would equate to for the leak jet size.  I am going to swap with my KTM shortly (R&D PowerBowl) before I sell the pumpkin.

I have not touched the AP linkage or any of the timing from what was set as stock on the 450R.

Mine runs great, with only one caveat: every now and then I can get some fuel starvation at high rpms/long sustained open throttle situations.  Switching over to the R&D bowl should fix that: I never got around to putting in an F2 bowl cap like I had planned.  I have never hooked up the hot start.  When cold I typically can give the bike a short shot or two of fuel from the AP and it will fire right up (so yes, I almost never ever use the choke).  It may die once, but then it restarts right away and is good to go.  When hot it always starts first kick.  A crash may take two kicks.  Depending on changing conditions, I may get a hanging idle, however that is cured with a simple 1/4 turn adjustment of the fuel screw.

 

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i do have the 07 crf450r carb. i was told to change the needle but this carb needle looks different like the one in photo 4,to the right

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I have a fcr bored to 42.5mm on my high comp hrc cam xr628r and set it up with a 42 pilot (45) was to rich NCVT needle in the 4th from top position 35 leak jet. I had it plugged but that was to much adjustable would be the way to go as I think I need about a 20-25 if they made them and I'm at a 165 main but plug showed I could go up on main after a WFO 4th gear pull plug chop. will try a 172 this summer when I dust it off to do some dual sporting 🙂 Thing really moves for a big old pig!

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6 hours ago, fixy said:

i do have the 07 crf450r carb. i was told to change the needle but this carb needle looks different like the one in photo 4,to the right

 

imageproxy.jpg

I'm not really sure what you have going on there.  Honestly, the parts on the right don't look like any CRF450 (or 250) that I can remember working on.  My CRF450R carb's parts look like those on the left: completely flat top with the needle holder that has the internal allen to tighten it down.  My KTM carb parts look the same as that of the Honda spec carb I have.

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That is the 2007 and later needle assembly

You just have to change to the 2006 or before brass capture nut and spring, if you want to use other needles than stock. Or any year 450X brass. Or any year WR, or any YZ.

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thanks guys. i just hope that more people will chime in and that someone who does have this year carb can say what they have done. i find that lots of people who have the same bike as ours don't like to share the progress so that others can have a more easier time with the carbs and help to encourage and inspire others to try and to enjoy their bikes. its sad to see that people come onto the forum and sites an rant about they progress but yet are not sharing the knowledge. to all that took the time out to comment,thanks a lot for your help and contributions.we all have superb machines:ride:

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