122 Persistent high idle
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    1. #1

      122 Persistent high idle

      Hey, all. I posted this in my introduction thread, but I feel here is more appropriate. I will post pics of the car later.

      Iíve been enjoying this car as a mostly daily driver these last few years. Got some major body work done, etc.

      These past few months, Ive been struggling with an untamable high idle. The newer SUís are rebuilt. Some details about the car:

      -engine was rebuilt several years back by a reputable source. Under load at high speeds, she ran excellently.

      -carbs are rebuilt. If I put on the old, tired ones, I still get the same result. Iíve replaced every hose I can, PCV valve, I even sprayed carb cleaner all over the place and can never find an air like.

      -if I disconnect the hose from the PCV valve to the nipple at manifold, and plug nipple,there is no change.

      -idle screws turned all the way out, still no change.

      -Pertronix electronic ignition less than a year old, was working fine as far as I know.

      -new Beru Blue coil, 12v 3 Ohm(I plan on getting the Bosch later)

      -iPD plug leads all just a few ,on this old

      -cap and rotor look good, theyíre newer.

      -brand new spark plugs gapped at .028

      -valves all at .020

      -idle timing is at 10 degrees, I did the static timing thing. Drive pinion is all correct.

      -distributor with centrifugal advance seems to be working fine. Springs are intact and functional.

      -battery, alternator etc all good.

      -carb pistons move the same, give a nice clunk when let drop.

      -throttles open and close all the way. Dashpot fluid etc good. Linkage seems to be okay.

      -if I pop open the float bowls after running it, they at the level they should be at.

      -choke is completely disconnected and disengaged.

      -I recently redid the head gasket. Lifters were all healthy as far as I know. All valves opened and closed as they should. Cleaned and replaced gasket with correct torques, etc, valve adjustment after.

      When trying to tune the carbs, the rear carb seems to pull in way more air than the front carb for what ever reason. If I pull the plugs, that side of the engine shows me itís running super lean. Those plugs are whiter and dry, front 2 a nice brown.

      And so, Iím finally returning to the forums for some help. Iím at a complete loss, here.

      Anyone here might have any idea as to what Im missing here? Iíve noticed the idle drops a bit when under load, but only because itís under load.

      I can drive it but it lacks any gusto. I plan on doing a compression test later in the week.

      Thanks, everyone.

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    3. #2
      Junior Member scaramoucheii's Avatar
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      Quote Originally Posted by Wtarkington77 View Post
      ork done, etc.

      These past few months, Ive been struggling with an untamable high idle. The newer SUís are rebuilt. Some details about the car:

      -carbs are rebuilt. If I put on the old, tired ones, I still get the same result. Iíve replaced every hose I can, PCV valve, I even sprayed carb cleaner all over the place and can never find an air like.
      Odd that both sets of carbs result in the same scenario, which points to the issue being somewhere else, but I have to ask

      ē Do you know what jets and needles are in the Carbs, where they replaced with the Carb Overhaul. If they are worn they will let in more fuel at idle and wrong ratio at ALL throttle settings. If they are worn and the float is set a tad high could cause issues.

      ē Do your Throttle plates have the anti stall spring loaded discs in them There is some good info on this on Ron's website

      https://www.sw-em.com/SU_Carb_Thrott...ly_vs_Late.htm


      ē When you say that you sprayed Carb Cleaner "All over the place" did you specifically target the Throttle Shaft bushings (all 4) and the Intake Manifold to head interface gasket? Can you confirm that the Throttle Shaft & Bushings were inspected and serviced as required during the Carb Overhaul?

      ē Also, have you double checked the Choke linkage and mechanism? you Didn't mention that. I'm a lot more familiar with the HIF6 carb, which has a "choke" cold start valve, AND screw that increases the idle, which adds a richer increased volume of mixture, Have you gone over that arrangement on your HS6's?

      ē Are you using the stock mechanical fuel pump? Have you checked it's pressure?
      Currently: 2016 XC90 T8, 1973 1800ES Original D-Jet, 1973 142 B20B, 1977 242 B230FT
      Previously: 1974 144 B20B, 1974 142 B20F, 1989 740, 1981 242 GLT, 1996 740, 1999 V70

    4. #3
      Junior Member
      Join Date
      Apr 2016
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      440
      W;

      "rear carb seems to pull in way more air than the front carb for what ever reason" ...I presume you know this because the Dashpot is much higher on the rear Carb when engine is running and Air Cleaners are off...it sounds like Throttle is not completely closed or False Air ( https://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air )is being alloed somewhere...I'd have a much closer look at that rear carb...if rebuilt, was the correct Throttle Plate installed (all "rebuilds are not allike! See: https://www.sw-em.com/SU_Carb_Thrott...ly_vs_Late.htm ) and does it, and linkage allow it to close completely? Compare Dashpot springs...they should both be Red (but often, the color is no longer visible...in that case compare length of the two, which should be near or equal. Is TOV possibly dislodged and stuck open allowing air to be pulled in ( https://www.sw-em.com/SU_Carb_Thrott..._Overrun_Valve ).

      Scara; Thanks for reference!

      Good Hunting!

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    6. #4
      Quote Originally Posted by scaramoucheii View Post
      Odd that both sets of carbs result in the same scenario, which points to the issue being somewhere else, but I have to ask

      ē Do you know what jets and needles are in the Carbs, where they replaced with the Carb Overhaul. If they are worn they will let in more fuel at idle and wrong ratio at ALL throttle settings. If they are worn and the float is set a tad high could cause issues.

      ē Do your Throttle plates have the anti stall spring loaded discs in them There is some good info on this on Ron's website

      https://www.sw-em.com/SU_Carb_Thrott...ly_vs_Late.htm


      ē When you say that you sprayed Carb Cleaner "All over the place" did you specifically target the Throttle Shaft bushings (all 4) and the Intake Manifold to head interface gasket? Can you confirm that the Throttle Shaft & Bushings were inspected and serviced as required during the Carb Overhaul?

      ē Also, have you double checked the Choke linkage and mechanism? you Didn't mention that. I'm a lot more familiar with the HIF6 carb, which has a "choke" cold start valve, AND screw that increases the idle, which adds a richer increased volume of mixture, Have you gone over that arrangement on your HS6's?

      ē Are you using the stock mechanical fuel pump? Have you checked it's pressure?

      Sorry, Iím still figuring this forum out.

      Thanks for the response. They came with ZH needles but I switched to KD. Should I switch back? Not sure exactly what jets. My throttle plates donít have the spring in them. Thatís good info about the plates, I didnít know there was different kinds. Iíll pull em later and check. Thank you!

    7. #5
      Quote Originally Posted by Ron Kwas View Post
      W;

      "rear carb seems to pull in way more air than the front carb for what ever reason" ...I presume you know this because the Dashpot is much higher on the rear Carb when engine is running and Air Cleaners are off...it sounds like Throttle is not completely closed or False Air ( https://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air )is being alloed somewhere...I'd have a much closer look at that rear carb...if rebuilt, was the correct Throttle Plate installed (all "rebuilds are not allike! See: https://www.sw-em.com/SU_Carb_Thrott...ly_vs_Late.htm ) and does it, and linkage allow it to close completely? Compare Dashpot springs...they should both be Red (but often, the color is no longer visible...in that case compare length of the two, which should be near or equal. Is TOV possibly dislodged and stuck open allowing air to be pulled in ( https://www.sw-em.com/SU_Carb_Thrott..._Overrun_Valve ).

      Scara; Thanks for reference!

      Good Hunting!
      The mighty Ron Kwas! Iíve seen your name on many posts while doing research. Thank you for responding! Yes, with the filters off I can see the rear piston rising just a little more. I actually just put in brand new red springs in each piston. My throttle plates donít have TOVís. Needles are KD. As far as I know the choke is completely disconnected and disengaged. The jets are up in normal position. Later I will look and see if the plates are the same.

      Can the fuel pump be a cause? The mechanical pump was replaced during the rebuild. I also have one of those little mechanical ones under the driver side of the car. I have a replacement. Can that be an issue?

    8. #6
      Quote Originally Posted by scaramoucheii View Post
      ē Are you using the stock mechanical fuel pump? Have you checked it's pressure?

      Iím using the mechanical fuel pump, but when I bought the car there was an electric one underneath the car, on the drivers side. I have a replacement for it. Should I replace it or get rid of it all together?

    9. #7
      Junior Member
      Join Date
      Apr 2016
      Posts
      440
      W;

      I don't know about "mighty", I'm just trying to help keep a few Swedish cars going, and helping owners use methodical troubleshooting to do it!

      ...I just don't see how a fuel pump can cause a "persistent high idle"...I'd keep looking at the carbs, adjustment, linkages, and manifolding...including PCV Sys...it wouldn't be the first time that a PCV Sys, which is supposed to be flow-limited, but which wasn't, resulted in a fast idle (its then a source of "False Air", see: https://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air) ...but False Air coming in by way of PCV Sys would not raise carb Dashpot...if Dashpot is raised, it still sounds like throttle is not closed...I lost an external throttle return spring one time resulting a high idle... obviously, check for those (early carbs had them in the open, where they can get dislodged and even lost, later carbs had them captive on throttle shafts, where they are a lot less likely to get lost)...and make sure all linkages are lubed and can return after the movement of opening...

      Good Hunting!
      Last edited by Ron Kwas; 10-19-2020 at 06:20 PM.

    10. #8
      Quote Originally Posted by Ron Kwas View Post
      W;

      I don't know about "mighty", I'm just trying to help keep a few Swedish cars going, and helping owners use methodical troubleshooting to do it!

      ...I just don't see how a fuel pump can cause a "persistent high idle"...I'd keep looking at the carbs, adjustment, linkages, and manifolding...including PCV Sys...it wouldn't be the first time that a PCV Sys, which is supposed to be flow-limited, but which wasn't, resulted in a fast idle (its then a source of "False Air", see: https://www.sw-em.com/su_carbs.htm#SU_Carbs_False_Air) ...but False Air coming in by way of PCV Sys would not raise carb Dashpot...if Dashpot is raised, it still sounds like throttle is not closed...I lost an external throttle return spring one time resulting a high idle... obviously, check for those (early carbs had them in the open, where they can get dislodged and even lost, later carbs had them captive on throttle shafts, where they are a lot less likely to get lost)...and make sure all linkages are lubed and can return after the movement of opening...

      Good Hunting!

      So I got the timing all straightened out. It lacks any kind of power when driving. I pulled all the spark plugs and the last one is clean and shiny, as if running very very lean.

      I ended up doing a compression test, and all 4 cylinders show about 135-145 psi. I know thatís low, thatís approximately 25% loss of compression on all 4. It bumped up just a bit after adjusting the valves. Could I have possible valve issues?

    11. #9
      Junior Member
      Join Date
      Oct 2018
      Location
      San Diego, CA.
      Posts
      478
      I bet it's worn out carb body at the throttle shafts. Saw it before. Most "rebuilt" carbs don't do the throttle shaft holes. They need to be reamed with the proper ream and then a steel bushing pressed in. That bushing then must be reamed to "line bore" the new bushings to make sure the throttle shafts don't bind. To determine if the carb body is worn, push/pull the throttle fore- and aft in the direction of the airflow. If idle varies, it's the carb body and shafts.
      IF the carbs were reamed and bushed, the likely suspect becomes the bushings themselves. If they are pushed in too far, there's no getting the butterflies in. If pushed in to the point where the bushings are just flush with the bore on the horizontal axis, there will be gaps at the top and bottom of the bushingi bore that will allow air to bypass the butterflies, and still draw fuel from the venturi. You must have both fuel and air to have higher RPM.
      The solution is to push the bushings in far enough so the bushing is flush with the bore at the top of the bore, and extends into the venturi on the horizontal plane. Then, the bushings must be meticulously filed or ground so they are perfectly flush with the carb bore.You don't want to cut any of the carb bore, since you'll have exactly the same problem as you do now.
      One other possibility is that the butterflies are simply not installed correctly. If the carbs re removed and the dashpot is out, you should see no light around the butterfly with a strong light behind it, but that's in the bonehead realm of carb overhaul. You could see the light past the bushing where it doesn't conform to the profile of the carb bore, that way, too.
      Last edited by Capndirk; Yesterday at 02:15 PM.
      2009 XC90 FWD 3.2, 2013 S60 T5
      In the past: '89 745, '91 940, '82 242, '67 122S, '67 123GT, '71 142E, '62 PV544.

    12. #10
      Quote Originally Posted by Capndirk View Post
      I bet it's worn out carb body at the throttle shafts. Saw it before. Most "rebuilt" carbs don't do the throttle shaft holes. They need to be reamed with the proper ream and then a steel bushing pressed in. That bushing then must be reamed to "line bore" the new bushings to make sure the throttle shafts don't bind. To determine if the carb body is worn, push/pull the throttle fore- and aft in the direction of the airflow. If idle varies, it's the carb body and shafts.
      IF the carbs were reamed and bushed, the likely suspect becomes the bushings themselves. If they are pushed in too far, there's no getting the butterflies in. If pushed in to the point where the bushings are just flush with the bore on the horizontal axis, there will be gaps at the top and bottom of the bushingi bore that will allow air to bypass the butterflies, and still draw fuel from the venturi. You must have both fuel and air to have higher RPM.
      The solution is to push the bushings in far enough so the bushing is flush with the bore at the top of the bore, and extends into the venturi on the horizontal plane. Then, the bushings must be meticulously filed or ground so they are perfectly flush with the carb bore.You don't want to cut any of the carb bore, since you'll have exactly the same problem as you do now.
      One other possibility is that the butterflies are simply not installed correctly. If the carbs re removed and the dashpot is out, you should see no light around the butterfly with a strong light behind it, but that's in the bonehead realm of carb overhaul. You could see the light past the bushing where it doesn't conform to the profile of the carb bore, that way, too.
      Hopefully your right. Seems more simple than valve work, for sure. I feel Iíve done all that I can with my limited knowledge, so Iím hoping to have it looked at by a pro, now.

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