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Rochester 2g Sticking Above Idle

Discussion in 'Flat Fender Tech' started by jwinsley, Dec 4, 2019 at 12:58 AM.

  1. Dec 4, 2019 at 12:58 AM
    jwinsley

    jwinsley Member

    Kauai
    Joined:
    May 4, 2011
    Messages:
    81
    Has anyone had this Rochester 2 barrel 2G issue, have searched and not found anything. After replacing my 2 barrel cast intake manifold with an aluminum edelbrock (225 v6) my carb started sticking above idle (sticks at 1100 RPM) when I take my foot of the gas. If I blip the throttle I can usually get the engine to drop down to idle, 6-700 RPM but that’s annoying to have to do at every stop. I can open the hood, rev it up by hand a little and see that the idle stop screw doesn’t quite come back to the stop (the cam) when I let it go. If I give the linkage a little push it does return to the stop. If I turn the motor off and try the same thing the carb returns, to what would be idle (with the idle stop hitting what it should for proper idle) without needing the little push.

    The only redeeming thing about this is that post manifold swap its pretty hard to get the motor to come off idle with the gas pedal. Hard enough that’s it tricky to get the jeep moving smoothly. I have pulled apart the carb and the throttle plate and shaft move freely and I don’t feel any obvious binding.

    Its almost like engine vacuum is trying to hold the throttle plates in closed position when coming off idle but I don’t know why that would affect the return action. I don’t want to add another return spring since that would make it harder to get off idle and it returns to idle position with the motor not running as is.
     
  2. Dec 4, 2019 at 10:31 AM
    Focker

    Focker That's what I do, I know things and I fix stuff. Staff Member Sponsor 2019 Sponsor

    Tri-Cities WA
    Joined:
    Aug 18, 2014
    Messages:
    6,221
    Sounds like a linkage issue.

    What if you disconnect the pedal linkage/cable and see what happens? :shrug:
     
    47v6 and jpflat2a like this.
  3. Dec 4, 2019 at 11:57 AM
    jpflat2a

    jpflat2a what's that noise?

    Riverside CA
    Joined:
    Jul 30, 2003
    Messages:
    7,832
    So you have an aluminum 2BBL manifold ?
    A little more info or clarification please.
     
    47v6 likes this.
  4. Dec 4, 2019 at 12:29 PM
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

    Denver, CO
    Joined:
    Jul 18, 2013
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    2,433
    Might help to clarify is this is a manual choke 2g, or auto choke?
     
    47v6 likes this.
  5. Dec 5, 2019 at 1:45 AM
    jwinsley

    jwinsley Member

    Kauai
    Joined:
    May 4, 2011
    Messages:
    81
    Lets see, aluminum 4 barrel intake, manual choke. I have watched the choke, aside from moving the choke plates I only see it moving the cam the throttle stop hits to adjust cold idle.

    My linkage only pulls, its actually high tensile strength kite line, but I have tried without that. Same result.

    I did come across one page which said worn throttle shafts or the hole the throttle shaft runs through can cause this. When there is no vacuum the plates rotates freely since there isnt really any force on the shaft but then with vacuum the out of round throttle shaft gets pulled against the hole causing sticking ( or the round shaft gets pulled against out of round hole) also sticking.
     
  6. Dec 5, 2019 at 10:02 AM
    OzFin

    OzFin Vintage Jeep Guy

    Michigan
    Joined:
    Jul 16, 2007
    Messages:
    541
    One way to check the shaft bushings is to warm up the engine and then while at idle spray carb cleaner directly on the shaft / bushing area...if the shaft is worn significantly the carb cleaner will make it past the annular area between the outside of the shaft and the inside of the bushing and get sucked into the intake thus resulting in the engine RPM changing.
    I would think that if the shaft / bushing is worn enough to create a sticky return throttle then its worn enough for this procedure to work as a diagnostic procedure.

    You could also remove the linkage and return spring, then grasp the throttle connection and physically push it around back & forth and in & out to see if the shaft has any excessive "wiggle room" to it.


    *Edited to correct my fat finger keyboard typing mistakes, but upon doing so I also read FinoCJ's post and I agree, if it was working before and now the problem shows up after the intake swap then that would suggest that the issue is a result of something done during the swap.-Oz
     
    Last edited: Dec 5, 2019 at 12:17 PM
  7. Dec 5, 2019 at 10:51 AM
    FinoCJ

    FinoCJ 1970 CJ5 Staff Member Sponsor

    Denver, CO
    Joined:
    Jul 18, 2013
    Messages:
    2,433
    I am kind of just throwing out thoughts, but if it was working fine before the intake swap, then it seems like something with the intake swap is causing the issue...I am assuming that as you swapped to a 4bbl intake that you needed some sort of adapter between the carb and intake? Could something with the adapter or base gasket at the bottom of the carb be interfering with throttle plate in some way - just enough to not let it move completely freely?
     
    OzFin likes this.
  8. Dec 5, 2019 at 1:57 PM
    ITLKSEZ

    ITLKSEZ Volvophilic

    Post Falls, ID
    Joined:
    Aug 13, 2015
    Messages:
    3,458
    My bet would be on a vacuum leak.

    Take your fan belt off and go around the manifold’s seals and carb base with an unlit propane bottle while listing for an idle increase.
     
    Bowbender likes this.

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