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Jetting for humidity? Any jetting specialists out there?

Discussion in 'Fuel' started by LuckyStar64, Jun 30, 2017.

  1. LuckyStar64

    LuckyStar64 PR Addict

    What's up gang!! If you know me-- you know I'm obsessed with play riding on trail bikes. So I have my '07 CRF230F set up with an '05 carb, jetted at 48/120, stock '05 needle with the clip in the 4th position down, air screw set at 1 and 1/2 turns out as what's described as "optimal" via countless dyno runs done by Mike Coe. The bike has run flawlessly. Last night with higher heat and humidity-- it started sputtering on top?? What exactly is happening with higher heat and humidity? My own minimal logic tells me that this richens the mixture due to denser air, and water content? I'd THINK you'd have to go a half turn OUT on the air screw at that point to lean out the mixture? It ran like it was running out of gas though? So the question is-- what needs to be done to compensate for high heat and humidity? Kinda confusing? --L*64
  2. BriarcliffMx

    BriarcliffMx PR Founding Father

    Down a main jet and try that
    jpelaston likes this.
  3. hershey

    hershey PR Elite

    Ozone Layer
    Racing Number:
    High heat makes your mixture richer because the air expands letting less oxygen molecules in. Then the high humidity adds water into the mix taking up more room leaving even less room for oxygen. If it were starving for fuel it would go flat, lose power or maybe even bog. Breaking up is rich.

    Like the prep guru stated, lean your main jet one step. One thing to consider, the testing that gave you the specs youre running may have been at a lower altitude than we are, that would require richer jetting than we need so you may already be a bit richer than it should be and this weather put you over the edge.
    jpelaston likes this.

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