Oil or Fuel? Need help diagnosing carbon buildup...
  • toofiddy
    Posts:2
    Joined:Sun May 29, 2016 9:29 am
    Oil or Fuel? Need help diagnosing carbon buildup...

    by toofiddy » Mon May 30, 2016 2:54 pm

    I recently bought an 06 250X with the following motor work done to it:

    08 R cam/head
    Wossner 13.5:1 piston
    "Special" carb tune by Eddie Cruz Racing in Long Beach CA
    4"x4" cutout on top of airbox, top triangle cutout on left side
    Twin-air air filter
    Stock header, FMF Q4 pipe w/ spark arrestor

    The jet/needle set up is as follows:
    172 main
    42 pilot
    68 leak
    NCYS needle, clip in 6th position down from top

    The bike starts and runs fine, but the idle is high and I notice slight bog at lower RPM (nothing severe). I ride at 4000'-8000'.

    Now to the problem. I recently pulled the plug to check it, and found it was wet and black, lots of carbon buildup on it. I also peeked down into the cylinder, and the face of the piston looks the same way, dark black flaky buildup that looks wet. It does not burn oil or smoke, and after some research it seems like this carb set up is very rich for my altitude. Will an overly rich mixture produce these types of buildups? What about an overly oiled air filter?

    I am going to do a compression/leak down test as soon as I can pick up a gauge. If the leak down test indicates blow by or bad valve seals/guides, that will answer my question, but I'm wondering if mixture could do this too. Any help is appreciated.
  • User avatar
    JimDirt
    Posts:4406
    Joined:Sat Nov 25, 2006 6:31 pm

    by JimDirt » Mon May 30, 2016 5:15 pm

    Welcome to the site !! \:D/

    Yea that sounds quite a bit rich , i would think somewhere in the 140 to 155 range would be more appropriate and the Needle Clip more towards the 3rd to 4th position

    Its running high because its rich and it is most likely running Hot (temp wise/overheating) as well

    Leaner it will run cooler and definitely not be sooty , the bog would also indicate rich , since a lean condition would bog , but also pop and die

    A overly oiled filter will also change the air/fuel mixture unless you compensate for it thru leaner jetting , but it still makes it harder to tune , since the oil will dissipate , it becomes leaner , especially if riding in hotter temps where the filter oil thins out , so you actually have a combination of things that are each contributing to your symptoms
    2020 CRF450R
    2006 CRF450X
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    Weiser , Idaho
  • Aussiecrf230
    Posts:1964
    Joined:Fri Jan 06, 2006 11:11 pm

    by Aussiecrf230 » Mon May 30, 2016 11:04 pm

    Yes welcome toofiddy,

    Have to agree with Jim way rich, surprised you done have black spooge running out the exhaust like an over rich KTM 2 stroke.
    Ray
    Australia

    CRF230F 2004
    C30F Power Up needle
    Mains 132
    Idle 45
    2 turns out
    Baffle out, Screens In

    It starts,it runs,it gets to where all CRFs can get to without the valve or valve plate dramas

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