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Technical Problem with Strom 97 butterflies wont close completely when running

Discussion in 'Traditional Hot Rods' started by shortshift, Mar 22, 2016.

  1. shortshift
    Joined: Nov 7, 2013
    Posts: 95

    shortshift
    Member

    Maybe someone has an answer...Have a couple of nice, rebuilt 97s on a basically stock 59A. Just converting from a couple of 48s. They both test good, running individual, but when I hook them together, the vacuum tends to not allow the butterflies to close all the way. If I shut off the engine, they will usually close all the way. I have added an extra return spring and that helps somewhat. It idles at about 600 rpm but when I hit the gas, the idle will not come down below 1000 rpm until I turn off the ignition. No binding in linkage. If I disconnect the accelerator pumps, its a little better, but not much. Thanks for any help/suggestions P1120717.JPG P1120715.JPG P1120717.JPG P1120715.JPG
     
  2. alchemy
    Joined: Sep 27, 2002
    Posts: 14,387

    alchemy
    ALLIANCE MEMBER

    The butterflies in my dual Stromberg setup never close all the way. Got to be open a little or you won't get anything through for it to idle on.

    If you had a 3-2 then you would need the outers to close all the way.
     
    LOU WELLS likes this.
  3. lowsquire
    Joined: Feb 21, 2002
    Posts: 2,564

    lowsquire
    Member
    from Austin, TX

    Usually its what engineers call 'tolerance stacking' ... Where you are trying to pull one carb back to idle through all the linkages, and all the little bits of slack add up and mean one carb wont fully return. the little stromberg return springs arent really strong enough Ive found, its probably a matter of adding a second return spring, one pulling on each carb.
     
    LOU WELLS likes this.
  4. shortshift
    Joined: Nov 7, 2013
    Posts: 95

    shortshift
    Member

    I figure that is probably what is happening. Will give the spring thing a try. Tks
     
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  5. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,912

    need louvers ?
    Member

    Also, take a bit of time and synchronise them and make sure they are closing at the same time and rate. Borrow or buy a Sync, take the linkage off between the carbs, set then the same, then hook the linkage back up and make sure each carb stays the same. If not adjust the linkage.
     
    big duece likes this.
  6. 48-760
    Joined: Dec 15, 2009
    Posts: 138

    48-760
    Member
    from OH

    I see you have the extra return springs on the two throttle shafts on the side tying the two carbs. together. If you move the linkage slightly more vertical there will be more spring pressure at the closed throttle position. Uncle Max also has HD springs for the accelerator fulcrums. I had to have both sets of springs on both carbs. Do the two carbs return to the same idle with the linkage from the carb to the firewall linkage disconnected? Is the spring on the firewall linkage in good condition and is the firewall linkage very free, clean & lubed. also place a small bit of light grease on the ball connection points and their linkage sockets, including the short rods on the throttle to fulcrums.
    By the way how does the engine run? What size mains and PV???
     
    Jeff34 likes this.
  7. deathrowdave
    Joined: May 27, 2014
    Posts: 1,833

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    My thinkin is PV is opening raising the idle . May need to change power valves , to help the issue
     
  8. shortshift
    Joined: Nov 7, 2013
    Posts: 95

    shortshift
    Member

    Thanks needlouvers...They close exactly the same. appears the vacuum is holding them open a bit because
    when u turn the ignition off, they close completely then...48-760 suggested adding more spring. I will try that
     
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  9. shortshift
    Joined: Nov 7, 2013
    Posts: 95

    shortshift
    Member

    Thanks 48-760 i will contact UMax and see about the springs. The carbs work great accept for the last little bit of closing...They WILL close after ignition is off, so suspect vacuum is helping keep them open a small amount
     
  10. Vacuum would tend to CLOSE the butterflys in my opinion,not make them stay open slightly
     
    oj and need louvers ? like this.
  11. john walker
    Joined: Sep 11, 2008
    Posts: 1,090

    john walker
    Member

    If the mechanical advance weights in your distributor don't return properly to idle position, due to being crusty or if the return springs are weak, it'll do the same thing.
     
    belair and need louvers ? like this.
  12. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,786

    Mike51Merc
    Member

    Strombergs have manual power valves that only open under nearly full throttle when the accelerator pump shaft bottoms out.
     
  13. alchemy
    Joined: Sep 27, 2002
    Posts: 14,387

    alchemy
    ALLIANCE MEMBER

    Yeah, I'm not getting the root of this problem. How can a carb close all the way and still idle? You do not want them to close all the way, unless one of them is part of a progressive system.

    Start you car up and take two long screwdrivers. Push the butterflies closed all the way and see what happens.
     
  14. 48-760
    Joined: Dec 15, 2009
    Posts: 138

    48-760
    Member
    from OH

    The throttle plates are not closed all the way at idle. The idle RPM adjustment screw will set the idle plates somewhat open. You would have to screw the idle level adjustment back until it did not touch the throttle linkage to get the plates completely closed. At that point the engine would most likely stall from trying to idle at extremely low RPM. I believe Sttromberg has a preliminary setting on the screw of about 3/4 turn open from first touch.
     
  15. 48-760
    Joined: Dec 15, 2009
    Posts: 138

    48-760
    Member
    from OH

    If you can help the linkage return to idle, manually, and the idle level is then consistently at the RPM adjustment you want it would appear the problem is slight sticking of the linkage. From your photo it would appear your car does not have many miles. New linkage can have some minor inherent binding this may disappear once you get some miles on the car. The addition of HD return springs can help get through this break in period. Once you get this idle problem straight do synchronize the Carbs.
     
  16. shortshift
    Joined: Nov 7, 2013
    Posts: 95

    shortshift
    Member

    I will check the sticking linkage...Everythin worrked great with the previous carbs. I will lube everything up real good and check for binding. Engine runs great, i am hoping i can just get it to return to actual idle when i let off the gas. I think Uncle Max HD return springs may work. Will give him a call...Thanks for all input.
     
  17. fiftiescat
    Joined: Jan 22, 2013
    Posts: 108

    fiftiescat
    Member
    from NY

    Did you ever figure out what’s going on? I’m having the same exact issue with 2 97’s on my 59A as well.


    Sent from my iPhone using H.A.M.B.
     
  18. fiftiescat
    Joined: Jan 22, 2013
    Posts: 108

    fiftiescat
    Member
    from NY

    Ever figure this out?


    Sent from my iPhone using H.A.M.B.
     
  19. fiftiescat
    Joined: Jan 22, 2013
    Posts: 108

    fiftiescat
    Member
    from NY

    I’m having the same exact problem with my 97’s and I’m stumped.


    Sent from my iPhone using H.A.M.B.
     

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