YZ250 jetting issues

Discussion in 'Thumpers' started by metal_ftw, Aug 26, 2017.

  1. metal_ftw

    metal_ftw Been here awhile

    Joined:
    Sep 3, 2015
    Oddometer:
    213
    Location:
    Oklahoma
    Hey guys, I am having trouble with jetting / carb setup on my YZ250 woods bike. I am planning to start doing some supermoto and light street use with it too if it makes any difference.

    First plug chop, lean:

    Main: 175

    Pilot: 50

    Power Jet: 50

    Needle: N3EJ

    Clip: 3rd position

    Pilot air: 2.5 turns out

    Fresh plug left me with what I thought was looking pretty lean, even though it was was still spooge city... Running H1R at either 36:1 or 40:1 (can't remember). 100% 91 oct. pump gas (best I can get around here)



    Did a second plug chop at:

    Main: 178

    Pilot: 50

    Power Jet: 50

    Needle: N3EJ

    Clip: 3rd position

    Pilot air: 2.5 turns out

    Plug from before was pretty clean still, re-used it. Still looked a little lean? I thought was looking pretty lean, even though it was was still spooge city... Running H1R at either 36:1 or 40:1 (can't remember). 100% 91 oct. pump gas (best I can get around here)



    Pics attached are from the second plug chop test with the 178 main.

    What really bothers me is I fouled a plug on the trails with the settings above with adjustments to the air screw settings. It fouled after going WOT, then coasting an applying low throttle, bike just went BLAAHHHHH and shut off. Never got it re-started. So now the fact it looks lean is really throwing me off...

    Attached Files:

    #1
  2. baloneyskin daddy

    baloneyskin daddy bikaholic Super Supporter

    Joined:
    Oct 21, 2009
    Oddometer:
    3,710
    Location:
    southcentral PA.
    Try dropping a size or 2 in the pilot jet. A lot of 2 strokes will load the plug up at low revs and foul out as soon as you try to clean them out.
    #2
    TomAZ1983 likes this.
  3. metal_ftw

    metal_ftw Been here awhile

    Joined:
    Sep 3, 2015
    Oddometer:
    213
    Location:
    Oklahoma
    Hmmm... I will have to try this.

    Any ideas on my lean bog after running WOT, then coasting, then reapply less than 50% throttle? Pretty sure it's lean because it's definitely bogging, not surging.
    #3
  4. JCool

    JCool Long timer

    Joined:
    Oct 15, 2016
    Oddometer:
    3,686
    Rich blubbers , lean surges.
    #4
  5. baloneyskin daddy

    baloneyskin daddy bikaholic Super Supporter

    Joined:
    Oct 21, 2009
    Oddometer:
    3,710
    Location:
    southcentral PA.
    Could be float adjustment issue or fuel flow problem,running floatbowl nearly dry when wide open for extended period.Also check the main jet and bottom of bowl for any flakes of dirt. I've had them get into a main jet and act like a butterfly valve.One moment gas will flow and the next the flake turns sideways and blocks flow. They're usually rust flakes from old metal tanks or gas cans and deteriorating petcocks and fuel filters.
    #5
  6. juicy flawless

    juicy flawless Toxic Raccoon

    Joined:
    Sep 10, 2014
    Oddometer:
    527
    @metal_ftw

    Forget about spark plug porcelain color, muffler spooge, piston wash deposits etc.

    Those hearsay rumors clogged up valuable internet space since the creation of social networking.

    Here's a viable method http://www.mopedarmy.com/wiki/HFFS
    #6
    JCool likes this.
  7. metal_ftw

    metal_ftw Been here awhile

    Joined:
    Sep 3, 2015
    Oddometer:
    213
    Location:
    Oklahoma
    #7
  8. juicy flawless

    juicy flawless Toxic Raccoon

    Joined:
    Sep 10, 2014
    Oddometer:
    527
    #8
  9. metal_ftw

    metal_ftw Been here awhile

    Joined:
    Sep 3, 2015
    Oddometer:
    213
    Location:
    Oklahoma
    Ah! Mine does that occasionally now when running lower rpm, crusing trail head parking lot.
    #9