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GS 1000 CV carbs hesitation around 2500 rpm

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    #1

    GS 1000 CV carbs hesitation around 2500 rpm

    I recently added a 4 into 1 exhaust on my GS 1000 ST and since then, the engine will hesitate when accelerating ( slowly) from 2500 rpm.
    The problem seems worse when the engine is hot.
    The bike will also not take full throttle below 6000 rpm but pulls strongly to red line.
    The idle runs perfectly.
    The bike is equipped with Dynoman pods, Dynojet stage 3 kit and Jama exhaust.
    The hesitation remains with a Kerker 4 into 1 exhaust.
    Main jets are 147.5 ( Mikuni size) then 142.5 ( no change) and needles in 3rd position from top.
    When needle was in 2nd position hesitation was much worse and stopped only above 6000 rpm.
    I suppose, I will have to try the needles in 4th position ( i.e.richer)?
    Any suggestion?
    sigpicJohn Kat
    My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
    GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020
    Tags: None
    #2
    My only suggestion would be to tell us what the throttle setting is when you are experiencing your problem.

    Engine RPM does not have nearly as much to do with problems as the actual throttle opening.

    Example: sitting in neutral on the centerstand, it does not even take 1/4 throttle to hit the red line.
    Or, you can be in fifth gear at 20 mph (which is less than 1500 RPM), and hit full throttle, trying to go faster.

    .
    sigpic
    mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
    hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
    #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
    #2 son: 1980 GS1000G
    Family Portrait
    Siblings and Spouses
    Mom's first ride
    Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
    (Click on my username in the upper-left corner for e-mail info.)

    Comment

      #3
      Originally posted by Steve View Post
      My only suggestion would be to tell us what the throttle setting is when you are experiencing your problem.

      Engine RPM does not have nearly as much to do with problems as the actual throttle opening.

      Example: sitting in neutral on the centerstand, it does not even take 1/4 throttle to hit the red line.
      Or, you can be in fifth gear at 20 mph (which is less than 1500 RPM), and hit full throttle, trying to go faster.

      .
      Yes, I should have mentionned that
      The hesitation occurs at 1/4 of throttle opening.
      sigpicJohn Kat
      My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
      GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

      Comment

        #4
        What do you know about tuning Mikuni CV carburetors?


        Life is too short to ride an L.

        Comment

          #5
          I've read most of the litterature including of course the Dynojet documentation
          Clearly at 1/4 throttle opening, it should eitheir be the needle or the pilot jet?
          The issue is always is it too rich or too lean?
          Given that the bike can't take wot until 6000 rpm does this mean too lean?
          I've now moved the needle up to the 4th position and I'll try again tomorrow if it doesn't rain?
          sigpicJohn Kat
          My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
          GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

          Comment

            #6
            Isn't the 4th position the one that is recommended by DynoJet?

            Keep in mind that it's the 4th position from the blunt end of the needle, not the pointy end.

            .
            sigpic
            mine: 2000 Honda GoldWing GL1500SE and 1980 GS850G'K' "Junior"
            hers: 1982 GS850GL - "Angel" and 1969 Suzuki T250 Scrambler
            #1 son: 1986 Yamaha Venture Royale 1300 and 1982 GS650GL "Rat Bagger"
            #2 son: 1980 GS1000G
            Family Portrait
            Siblings and Spouses
            Mom's first ride
            Want a copy of my valve adjust spreadsheet for your 2-valve per cylinder engine? Send me an e-mail request (not a PM)
            (Click on my username in the upper-left corner for e-mail info.)

            Comment

              #7
              The reason I asked is that Mikuni CVs are tuned from the top down, you must get the main jets perfect first, then the jet needles and all of the others. The fact that you are still swapping mains from 142.5 to 147.5 tells me you haven't done this yet.


              Life is too short to ride an L.

              Comment

                #8
                Originally posted by Steve View Post
                Isn't the 4th position the one that is recommended by DynoJet?

                Keep in mind that it's the 4th position from the blunt end of the needle, not the pointy end.

                .
                No, Dynojet says " on groove #3 from the top"
                sigpicJohn Kat
                My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
                GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

                Comment

                  #9
                  Originally posted by tkent02 View Post
                  The reason I asked is that Mikuni CVs are tuned from the top down, you must get the main jets perfect first, then the jet needles and all of the others. The fact that you are still swapping mains from 142.5 to 147.5 tells me you haven't done this yet.
                  Many thanks, I didn't know about this
                  The reason, I downsized the main jet was because the spark plug electrode (?) has a nice brown color but at the thread's edge there was some black soot.
                  I felt I wasn't far off on the main jet as the bike pulls very strongly above 6000 rpm ( at wot) but I just wanted to make sure I was spot on.
                  FYI, there is no smoke coming out of the exhaust at any time.
                  If it still doesn't work tomorrow, I'll do a roll on test on the dyno and monitor the AFR.
                  sigpicJohn Kat
                  My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
                  GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

                  Comment

                    #10
                    Presume your ignition system is ok? Had similar symptoms on a 80 1000G that turned out to be the ignitor box...

                    What is it they say... about 80% of carb problems are ignition related
                    1980 GS1000G - Sold
                    1978 GS1000E - Finished!
                    1980 GS550E - Fixed & given to a friend
                    1983 GS750ES Special - Sold
                    2009 KLR 650 - Sold - gone to TX!
                    1982 GS1100G - Rebuilt and finished. - Sold
                    2009 TE610 - Dual Sporting around dreaming of Dakar.....

                    www.parasiticsanalytics.com

                    TWINPOT BRAKE UPGRADE LINKY: http://www.thegsresources.com/_forum...e-on-78-Skunk/

                    Comment

                      #11
                      Originally posted by salty_monk View Post
                      Presume your ignition system is ok? Had similar symptoms on a 80 1000G that turned out to be the ignitor box...

                      What is it they say... about 80% of carb problems are ignition related
                      You are right but I didn't have this symptom with the original exhaust
                      sigpicJohn Kat
                      My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
                      GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

                      Comment

                        #12
                        It worked
                        I tested the bike this morning with the needle on the 4th groove and I have:
                        ZE canyon carver
                        As much as I don't totally trust my std GS 1000 S this bike is a delight to ride in the fast twisties.
                        Here's a picture "as built"
                        Thanks for the support!
                        sigpicJohn Kat
                        My bikes: CB 77, GS 1000 ST Cafe Racer with GSXR 1052 engine, GS 1000 ST, XR 41 Replica with GS 1085 engine,
                        GS 1100 SZ Katana with GS 1135 EFF engine, KTM Superduke 1290 R 2020

                        Comment

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