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Re-jet Carburetor For High Altitude?

Discussion in 'Early CJ5 and CJ6 Tech' started by Buildflycrash, Jun 15, 2020.

  1. Jun 15, 2020
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

    Gulf Breeze FL...
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    Getting close to the Colorado trip and wanting to have the parts in hand to re-jet My carb. Can y'all let me know exactly what I need (link would be great)? We will spend the week in Silverton and more time in Leadville (over 10,000') Here's what I have.....

    [​IMG]

    And...


    [​IMG]
     
  2. Jun 15, 2020
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

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    Jet it down a couple of sizes, but also advance your timing 8 degrees over the factory setting.
     
  3. Jun 15, 2020
    Ohiowrangler

    Ohiowrangler New Member

    Newark
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    this company has treated me well in the past. In addition to jets I carry a rebuild kit(spare gaskets). Ron

    7040108 Carburetor Info Page
     
  4. Jun 15, 2020
    boopiejones

    boopiejones Member

    California east bay
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    Here’s a link to stock jet sizes for various Rochester 2G carbs. I don’t see the 7040108 listed, although I’m not sure it really matters as someone could have installed different jets over the decades since the carb was produced. the only foolproof way to know your current jet size would be to remove the top cover from your carb and see what size is stamped on the jets.
    Rochester 2 Jet Main Jet Specifications

    and here’s a link to purchase jets
    Rochester 2G, 2GC & 2GV 2 Barrel Carburetor Metering Jets
     
    Last edited: Jun 15, 2020
    Buildflycrash likes this.
  5. Jun 15, 2020
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    I'm not exactly sure what that means. I've never successfully taken apart a carburetor and reassembled. I guess its on to YouTube for me.
     
    Last edited: Jun 15, 2020
  6. Jun 15, 2020
    boopiejones

    boopiejones Member

    California east bay
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    You just need to remove the top cover and the jets will be visible at the bottom of the float bowl. Jet sizes should be stamped on top of the jets. There is a chance you will need to replace the gasket. Typically they’re reusable, but I wouldn’t take a carb apart without having a spare handy. Murphy’s law.

     
  7. Jun 15, 2020
    Jw60

    Jw60 Recovering Jeepaholic

    Sedalia MO.
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    Here are some good tricks to consider while it is open. Particularly closing one vent and the solid gasket to act as a baffle.
    I don't have the 2g but this stuck in my head as interesting.

    Thumper gets another Mod
     
  8. Jun 15, 2020
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    I would get a carburetor kit for your carburetor and then purchase 49 or 47 jets from reputable company.
    These are the factory recommended sizes for higher altitude.
    Remove the top of carburetor, use a slotted screwdriver to remove the jets; they are threaded.
    The carburetor kit is just in case you rip/tear the top cover gasket.
    You will have to disconnect some linkage, so be careful and be observant.
    Maybe snap a photo before, during, and after.

    EDIT: 51 is factory; 49 for over 5000 ft; 47 for over 10000 ft.

    I personally run 47's when in Colorado; in fact, they are still installed from last year's trip.
     
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  9. Jun 15, 2020
    homersdog

    homersdog Tulsa, Ok 2020 Sponsor 2019 Sponsor

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    I bought a couple different sizes from mikes carburetor parts a few weeks ago. The stock Dauntless 225 jets are .051. I bought .049's and .047's in anticipation of the Colorado trip. On a whim I put in the .049's here at home. We are about 700 altitude here. The .049's actually run better than .051's.

    Anyway you might buy a couple different smaller sizes and be ready to change them out at altitude. Remember you need qty 2 each

    Mikes carburetor parts has a great write up on selecting the correct jets.
     
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  10. Jun 15, 2020
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    I think I’m starting to feel like I could do this. I’m not thrilled about taking the carb apart but I’ll give it a shot. I’ll bet mine runs better on the .049 as well. it’s rich as it is.
     
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  11. Jun 16, 2020
    homersdog

    homersdog Tulsa, Ok 2020 Sponsor 2019 Sponsor

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    If it has been a while since you opened the carb,the top gasket will probably tear when you take the top off. Have a new one handy.
     
  12. Jun 16, 2020
    Buildflycrash

    Buildflycrash Member 2020 Sponsor

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    Got the two sets (.049 and .047) ordered from Mikes and a new Bowl Gasket. Priority Mail for $32 .
    Fingers crossed this thing runs when I'm done.
     
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  13. Jun 16, 2020
    colojeepguy

    colojeepguy Colorado Springs 2019 Sponsor

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    Don't forget to bump up the timing or you won't have any power.
     
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  14. Jun 16, 2020
    BobH

    BobH Member 2020 Sponsor

    Oviedo, Fl
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    I did the opposite with my 60 CJ5 (F134), went from 9000 ft in Colorado to 35 ft in Fl. What jets should I be using?
     
  15. Jun 16, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Do you have the YF? If it runs fine now you probably don't need to do anything.
     
  16. Jun 16, 2020
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
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    Your carburetor uses metering rods.
    The high altitude rods are hard to find.
    Ever looked to see which you have ?
     
  17. Jun 16, 2020
    jpflat2a

    jpflat2a what's that noise?

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    Very true.
     
  18. Jun 16, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

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    Since I never lived anywhere but Florida high altitude performance was something I never thought about until discussions on this forum. :D
     
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  19. Jun 16, 2020
    BobH

    BobH Member 2020 Sponsor

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    The plugs are black, haven’t done a compression test, but it runs fine.
     
  20. Jun 16, 2020
    Glenn

    Glenn Kinda grumpy old man Staff Member

    Apopka, Fl
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    Hmmmm, black sooty out of the exhaust? Blue smoke?
     

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