1. Registration trouble? Please use the "Contact Us" link at the bottom right corner of the page and your issue will be resolved.
    Dismiss Notice

Carburetor Adjustment - Rochester 2g

Discussion in 'Early CJ5 and CJ6 Tech' started by Steve's 70-5, Jun 26, 2018.

  1. Aug 12, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member

    WA
    Joined:
    Aug 18, 2014
    Messages:
    7,540
    Clean the carburetor if it's been sitting. Look at the power valve at the bottom of the carb. It's often overlooked.
     
  2. Aug 12, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    23,596
    Does a 2G have a power valve? It has some kind of low-vacuum-enrichment mechanism, which I thought was the vacuum-lifted tapered needles.

    Never mind - I'm thinking of the Carters. There is a "power piston" which I assume has the same function as the power valve in an Autolite/Motorcraft 21xx/41xx.
     
    Last edited: Aug 12, 2020
    Focker likes this.
  3. Aug 12, 2020
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
    Joined:
    Jul 18, 2013
    Messages:
    5,593
    yes - and that power piston sits on top of the needle in the power valve and can be a bit fiddly to get everything lined up just right when putting the top of the carb back on.....

    Going back to the OPs comment - I would guess its running too rich based on the plugs and stumble. If the accelerator pump checks out okay (2 streams as Oz mentioned above), then check the size of your main jets, and then check the power piston and power valve needle is not sticking open. In the case of mine, the PV was allowing fuel to feed directly into the carb throat even when the throttle plate was mostly closed causing a very rich condition (either was sticking open or there was junk under it and it was not seating down properly when threaded in). When activating the accel pump, it was just adding even more fuel, flooding and bogging the engine.....The test that kind of hinted that it was running too rich (in addition to the plug fouling) and pushed me in this direction: at idle, gently turn the idle screws all the way closed (don't over tighten them), and it while it would stumble just a bit, it kept running (it should have died), so fuel was getting through some other pathway.
     
  4. Aug 12, 2020
    iharding

    iharding Quitter

    Tacoma, WA
    Joined:
    Feb 24, 2013
    Messages:
    354
    My eBay rebuilt carb (FOR 225 JEEP DAUNTLESS L@@K!!!!!) came with 055 jets. 051 are standard for sea level I've been told.
     
  5. Aug 12, 2020
    Steve's 70-5

    Steve's 70-5 Active Member

    Louisville, Ky
    Joined:
    Nov 12, 2009
    Messages:
    1,381
    The comments everyone is making, it looks like a rebuild would be a good idea. I have a extra carburetor sitting in the cabinet. Going to rebuild it, there looks to be plenty of information on the web to do this. Then it will be a swap. Then rebuild the other carburetor and have a extra ready to go.
     
    OzFin, colojeepguy and Focker like this.
  6. Sep 7, 2020
    Steve's 70-5

    Steve's 70-5 Active Member

    Louisville, Ky
    Joined:
    Nov 12, 2009
    Messages:
    1,381
    Looking at the 2g carburetor I am going to rebuild. There is a outlet for a vacuum line. Is this supposed to be hooked up?
     
  7. Sep 7, 2020
    NCRenII

    NCRenII yellow fever

    Far Nor Cal
    Joined:
    Sep 22, 2017
    Messages:
    431
    Do pick up a new power valve and install. I've seen many rebuilds end up running with the same richness issue due to that part.
    Additionally make sure correct vented fuel cap is used and also that all fuel return lines are clear to tank.
    Last read the rebuild instructions and check weight of fuel float and adjust accurately.
    Re: timing, I don't believe initial timing is as important as total timing at full in vacuum and mechanical advance. Today's fuel blends often require additional initial timing as they do not combust (burn) as well as the old good stuff and will imitate a rich condition smell.
     
    Beach66Bum likes this.
  8. Sep 7, 2020
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
    Joined:
    Jul 18, 2013
    Messages:
    5,593
    that vacuum line connects to the vac can advance on the distributor - known as ported vacuum. Some prefer to hook the vac can to manifold vacuum- if so, then just plug/cap the carb vac port.
     
    Beach66Bum likes this.
  9. Nov 9, 2020
    Steve's 70-5

    Steve's 70-5 Active Member

    Louisville, Ky
    Joined:
    Nov 12, 2009
    Messages:
    1,381
    Rebuilt the carburetor and put it on, ran a little better, still a little rich, not running real good. Was fooling with the timing it ran better with timing about at 30 degrees. Drove it around and there was a little stumble and the running rich was not that bad.

    Put a 3 wire 12si alternator on this help some.
    Fooled with the Jeep again last night, adjusted carburetor with vacuum gauge, the highest I can get is 15. Adjusted timing and now at about 18-20 degrees. Drove it though the neighborhood and the carburetor would load up a little then clear out and and it drove good. Started the Jeep tonight after sitting about 24 hours, it started up after cranking the starter for about 2 seconds.

    Going to pull carburetor off and check float measurements.
     
    Focker likes this.
  10. Dec 3, 2020
    Steve's 70-5

    Steve's 70-5 Active Member

    Louisville, Ky
    Joined:
    Nov 12, 2009
    Messages:
    1,381
    Going to install new jets in the carburetor. Can I do this with the carburetor on the engine? I have new jets 49-50 and 51. What size should I use?
    Louisville is about 700-800 feet above sea level
     
  11. Dec 3, 2020
    colojeepguy

    colojeepguy Colorado Springs

    At the foot of...
    Joined:
    Apr 4, 2010
    Messages:
    7,111
    Sure, just need to remove the top of the carb.
     
  12. Dec 3, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
    Joined:
    Aug 10, 2003
    Messages:
    23,596
    Possible, but I would not. Too easy to remove the carburetor complete, and I drop things too often. Something goes down the manifold, and that's bad. No experience with the 2G, but I remove jets by screwing the carb down to my wooden bench. The jets can be tough - pick a tool that fits well and don't let it slip and mangle the brass of the jets. I have a screwdriver that I ground to remove the blade taper and fit the jet slots. Square shank, small crescent wrench, push down hard and turn with the wrench on the shaft. Pop.
     
  13. Dec 3, 2020
    colojeepguy

    colojeepguy Colorado Springs

    At the foot of...
    Joined:
    Apr 4, 2010
    Messages:
    7,111
    Good advice here...I have a similar screwdriver for AFB jets.
     
  14. Dec 3, 2020
    Steve's 70-5

    Steve's 70-5 Active Member

    Louisville, Ky
    Joined:
    Nov 12, 2009
    Messages:
    1,381
    I had the jets out when I rebuilt the carburetor about a month ago. They should come out easy
     
  15. Dec 3, 2020
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member

    Bozeman, MT
    Joined:
    Jul 18, 2013
    Messages:
    5,593
    I believe the OEM specs - 51 jets are for 0-2500' elevation, 50 jets are for 2500-5000', 49 jets are for 5000-75000' and so on...
    I have found with my engine after the rebuild, with a 252 comp cam, and some possible exhaust restriction, it likes to run just a bit richer than the OEM specs suggest, I run at least one jet size smaller....
    As its better to be a bit rich tan too lean, I'd start with the 51 jets and see how it runs and check the spark plugs....if its a bit rich, lean it out one jet size....
    As for changing the jets - it can be done on the jeep, but as mentioned above, I am always nervous I am somehow going to loose one down the carb throat - so be careful. I find getting the top/air horn off a bit finnicky with all the throttle linkage pieces - so sometimes it just easier to pull the entire carb off if you don't mind disconnecting the fuel inlet and doing it on the bench. If the existing jets haven't been removed in who knows how long, it might be easier/safer to do it on the bench as they can be a bit 'stuck'....
     
  16. Dec 3, 2020
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Western North...
    Joined:
    Dec 12, 2009
    Messages:
    873
  17. Dec 12, 2020
    maurywhurt

    maurywhurt Member 2024 Sponsor 2023 Sponsor 2022 Sponsor

    Western North...
    Joined:
    Dec 12, 2009
    Messages:
    873
    Also, here's a link to a Rochester 2bbl rebuilding guide I just came across in my digital stash:

    Rochester 2bbl Guide.pdf
     
  18. Dec 12, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member

    WA
    Joined:
    Aug 18, 2014
    Messages:
    7,540
  19. Dec 12, 2020
    Focker

    Focker That's a terrible idea...What time? Staff Member

    WA
    Joined:
    Aug 18, 2014
    Messages:
    7,540
    Nice. I'll add it to the Technical Index page. (y)
     
New Posts