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SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

posted by  someone claiming to be tommyt544 on  Sat Jun 2 17:22 CST 2018 [RELATED]

Hi Everyone,

Got me a pretty weird issue. Hope I can explain this properly:

I just had my HS6 carbs rebuilt and I've noticed that I have really terrible performance. No "pull" as I drive and it feels like I'm operating on 2-3 cylinders. This car used to have a lot of pep before the carb rebuild.

I've done the following:

valve lash
timing
checked wires
tuned carbs including checking the floats (both had same amount of fuel), adjusted and synched the throttle and fast idle screws.

The rear carb gets a lot of pressure and seems to be very responsive. The front does not and I can't seem to get it to match the performance of the rear.

Here are the things that are odd: The throttle shaft seems fused to the brass fork on the front carb, preventing it from moving independently when the throttle arm is pulled. Unlike the throttle arm of the rear carb where it moves the carb independently when pulled, the front arm only moves the ENTIRE carb shaft. The other weird thing is that the brass fork on the front carb is not level with the brass fork of the rear carb by about 3/4 of an inch higher. Theoretically it's unimportant because the pin can be loosened and adjusted to compensate but I'm wondering if there's something much more serious at play here.

Thanks! I appreciate all the help this forum has given me through the years.








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    SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

    posted by  someone claiming to be tommyt544 on  Wed Jun 6 11:06 CST 2018 [RELATED]

    Video for anyone interested:

    Excuse me calling the brass forks "Bronze". Now that would be an expensive carb!

    https://screencast-o-matic.com/watch/cF11bfbSAW








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    SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

    posted by  james_a_sousa on  Tue Jun 5 20:03 CST 2018
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Thu Oct 23 18:51 CST 2014
    [RELATED]

    Do both carbs more when you pull on the throttle linkage?

    I'll fiddle with my carbs tomorrow.








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      SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

      posted by  someone claiming to be tommyt544 on  Wed Jun 6 08:41 CST 2018 [RELATED]

      Both carbs pull at the same time (I can still adjust the pins in the forks to catch the shaft without play)
      When I pull on the accelerator arm attached to the spring on the rear carb, there's some play.
      When I pull on the accelerator arm attached to the spring on the front carb, it's stuck because the bronze fork was fused to the throttle shaft.
      The bronze forks are not at the same level so therefor the pins that go in them are not aligned either.







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        SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

        posted by  planetman on  Wed Jun 6 09:47 CST 2018
        Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
        last visit: Fri Oct 24 09:29 CST 2014
        [RELATED]

        Can you supply pictures or better yet, a short video?

        --
        Eric
        Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
        Torrance, CA 90502
        hiperformanceautoservice.com or oldvolvosonly.com








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          SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

          posted by  someone claiming to be tommyt544 on  Wed Jun 6 11:05 CST 2018 [RELATED]

          Excuse me calling the brass forks "Bronze". Now that would be an expensive carb!

          https://screencast-o-matic.com/watch/cF11bfbSAW








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            SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

            posted by  planetman on  Wed Jun 6 19:55 CST 2018
            Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
            last visit: Fri Oct 24 09:29 CST 2014
            [RELATED]

            Hello,


            You need to tighten the clamp on the central linkage for your REAR carburetor as it isn't tight enough. You will also need to sync the carbs at the same time.

            --
            Eric
            Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
            Torrance, CA 90502








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              SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

              posted by  someone claiming to be tommyt544 on  Wed Jun 6 20:21 CST 2018 [RELATED]

              You mean the pin that goes into the brass fork that should be at the bottom of the fork when tight?

              I should know more Friday as I'm taking the carbs back to the mechanic who rebuilt them for me. He's going to unfuse the brass fork and make sure everything will seat properly. Then back to synchronizing.








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                SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

                posted by  planetman on  Thu Jun 7 00:24 CST 2018
                Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
                last visit: Fri Oct 24 09:29 CST 2014
                [RELATED]

                Your problem is the bolt for the clamp for the REAR carburetor on the central linkage is not tight enough.


                --
                Eric
                Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
                Torrance, CA 90502
                hiperformanceautoservice.com or oldvolvosonly.com








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                  SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

                  posted by  derek uk on  Thu Jun 7 05:16 CST 2018
                  Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
                  last visit: Fri Oct 24 12:33 CST 2014
                  [RELATED]

                  100% agree. When you move the rear arm by hand as in the video the whole shaft connecting the carbs and the butterfly shafts should move as one. Yes you will need to resynch the carbs for equal flow before locking the clamps down. Loosen both clamps, adjust the carbs individually for equal flow at about 800-1000rpm and then lock down the clamps. A proper vacuum synchroniser best for this. listening to the hiss via a hose to the ear can work, but rather hit or miss. Adjust jets for mixture individually for best idle. Suggest 12 flats down as a starting point.








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                    SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

                    posted by  someone claiming to be tommyt544 on  Thu Jun 7 10:25 CST 2018 [RELATED]

                    Yeah in the video the bolts for the pins were loosened on purpose so that I could show you all that even when loosened the shaft doesn't release from the right brass fork. I'm aware that the rear pin was moving--it's usually seated at the bottom of the fork and secure.








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            SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

            posted by  Volvo From Heck on  Wed Jun 6 13:51 CST 2018
            Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
            last visit: Mon Oct 13 20:56 CST 2014
            [RELATED]

            I've been a bit confused by some of your terminology - even while looking at a set of carbs mounted on a manifold. I think after seeing the video the problem may be as "simple" as a not well centered throttle plate on the forward carb. Not being centered will cause the throttle to stick - and may even be the cause of the not aligned "forks". Sticking may be just enough that you can't open the throttle with the short return spring lever but loose enough to be able to do so with the longer throttle link. Not being centered will affect the ability to get the forward carb adjusted properly for mixture which in turn will affect its ability to deliver fuel evenly with the rear carb when driving.
            The forks should be even. I had a conversation with Joe Curto a while back and he explained that new replacement throttle shafts are no longer pre-drilled for the pins which hold the forks to the shaft and that he had the proper jigs to drill the holes in the correct spots. If your rebuilder drilled them correctly they should align the forks--if the throttle plates are centered. If the drilling was done by "eye" -- what else is not quite right? -- the throttle plate alignment? -- and??
            I think you need to remove the forward carb and confirm that the throttle plate is centered. -- Dave







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              SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

              posted by  someone claiming to be tommyt544 on  Wed Jun 6 15:48 CST 2018 [RELATED]

              This is the explanation I've been looking for. Thank you!








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        SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

        posted by  planetman on  Wed Jun 6 09:47 CST 2018
        Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
        last visit: Fri Oct 24 09:29 CST 2014
        [RELATED]

        Can you supply pictures or better yet, a short video?

        --
        Eric
        Hi Performance Automotive Service (formerly OVO or Old Volvos Only)
        Torrance, CA 90502
        hiperformanceautoservice.com or oldvolvosonly.com








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    SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

    uid 5322's pic
    posted by  alschnertz on  Sun Jun 3 04:36 CST 2018
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Fri Oct 24 10:32 CST 2014
    [RELATED]

    This doesn't mean that it's not a carburetor issue, but in addition to what you've done already;

    1. Check your fuel pressure - should be around 2-3 psi;
    2. Check the engine's compression.

    I'm having a difficult time understanding your description of the problem.
    If the car "had a lot of pep before the rebuild", why the rebuild?







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      SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

      posted by  someone claiming to be tommyt544 on  Sun Jun 3 08:08 CST 2018 [RELATED]

      The shafts were pretty worn so whoever had adjusted the carbs to make the car run had made it pretty rich to compensate. I thought I was getting ahead of the ballgame by bringing the car back to baseline.

      The fuel pressure is fine but haven't checked the compression. Only 7000 miles since a rebuild so I'm hoping it's not the engine...

      At the linkages that attach to the spring, I'm assuming (but may be incorrectly assuming) that since the rear one allows the carb to move independently on the shaft when it's pulled, the front should too. Currently the rear does but the front is froze and only moves both.







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        SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

        posted by  phonemanjames on  Tue Jun 5 18:35 CST 2018
        Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
        last visit: Thu Oct 23 20:02 CST 2014
        [RELATED]

        I agree that most of the previous suggestions are the likely culprit.........

        If you still have the glass bowl fuel filter, check that as well as you may also be suffering from fuel starvation.








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          SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

          posted by  someone claiming to be tommyt544 on  Wed Jun 6 08:38 CST 2018 [RELATED]

          I still do have the glass bowl fuel pump but I have plenty of fuel entering the carb floats at the same rate. I'll check the filter today to see if there's any issue.







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    SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

    posted by  c1800 on  Sat Jun 2 22:44 CST 2018
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Sun Oct 5 19:37 CST 2014
    [RELATED]

    Check with the rebuilder?








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      SU HS6 Carb Tuning: Fused Fork on Throttle Shaft on Front Carb and Terrible Engine Performance 444-544

      posted by  someone claiming to be tommyt544 on  Sun Jun 3 08:00 CST 2018 [RELATED]

      That's the next step. Trying to diagnose as much as I can before I get the issue on the shaft fixed.







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