Can anyone double-check/recommend my rejetting?

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  • G.S.Joe
    • Feb 2026

    #1

    Can anyone double-check/recommend my rejetting?

    My bike is coming together, and I'm having difficulty getting it to not cut-out. The previous owner started to cafe it but didn't finish. Carbs look stock (1978 GS750), and have 102 mains, slow is a 15. From what I'm reading with open manifold and pod filters I should be running 3 sizes bigger, so a 109.5 main, and a 17.5 slow jet.

    First, before I buy anything, can anyone confirm I'm going in the right direction? And, similarly, can anybody recommend a brand/seller?

    As always, thanks.
  • tom203
    Forum Guru
    Past Site Supporter
    • Aug 2010
    • 8925
    • Norway,Maine

    #2
    I'm not real familar with the VM carbs, but yes, with pods, you need to go up on mains; you probably have seen this chart from Basscliff



    Hang in there, someone knowledgeable will chime in
    1981 gs650L

    "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

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    • rustybronco
      Forum LongTimer
      Bard Award Winner
      GSResource Superstar
      Past Site Supporter
      • Jul 2005
      • 14961
      • Marysville, Michigan

      #3
      What do you mean by open manifold? No exhaust system whatsoever?
      De-stinking Penelope http://thegsresources.com/_forum/sho...d.php?t=179245

      http://www.thegsresources.com/_forum...35#post1625535

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      • allojohn
        Forum Sage
        Past Site Supporter
        Super Site Supporter
        • Jan 2011
        • 3515
        • NoMo, MN

        #4
        I run a 78 750 with K&N pods and V&H pipe. 15 pilot and 117.5 mains.
        -Mal

        "The only reason for time is so that everything doesn't happen at once." - B. Banzai
        ___________

        78 GS750E

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        • Guest

          #5
          Eric sent me this to help you out;

          Just tell him to buy the 107.5 and 110 main jets from Z1 Enterprises and keep the stock 15 pilot jet in them.
          Try the 107.5's first and adjust the fuel and air screws.
          That should be all that he really needs to do besides ride it.
          Edit: this is assuming you have stock exhaust.
          Eric

          He seems to know pods, that's about all he uses on his bikes.
          Last edited by Guest; 05-07-2013, 02:56 PM.

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          • G.S.Joe

            #6
            Originally posted by rustybronco
            What do you mean by open manifold? No exhaust system whatsoever?
            I'm afraid I'm new to bikes and I used the term in an automotive sense. I have what many might call "headers", but they're stock, so I refer to them as manifolds. Is that incorrect? I always thought headers = aftermarket manifolds.

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            • G.S.Joe

              #7
              Originally posted by gsrick
              Eric sent me this to help you out;

              Just tell him to buy the 107.5 and 110 main jets from Z1 Enterprises and keep the stock 15 pilot jet in them.
              Try the 107.5's first and adjust the fuel and air screws.
              That should be all that he really needs to do besides ride it.
              Edit: this is assuming you have stock exhaust.
              Eric

              He seems to know pods, that's about all he uses on his bikes.

              Thanks! I do have open headers or manifold, or whatever you want to call it. No mufflers.

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              • tom203
                Forum Guru
                Past Site Supporter
                • Aug 2010
                • 8925
                • Norway,Maine

                #8
                Originally posted by G.S.Joe
                I'm afraid I'm new to bikes and I used the term in an automotive sense. I have what many might call "headers", but they're stock, so I refer to them as manifolds. Is that incorrect? I always thought headers = aftermarket manifolds.
                The bike left factory with "headers" - something like you might put on a car that had a cheapo exhaust "manifold". But do you have mufflers attached to these headers? OOPs, I see your new post- no mufflers! This likely changes the jetting requirements- do you live in a noisy neighborhood?
                1981 gs650L

                "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

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                • rustybronco
                  Forum LongTimer
                  Bard Award Winner
                  GSResource Superstar
                  Past Site Supporter
                  • Jul 2005
                  • 14961
                  • Marysville, Michigan

                  #9
                  First, do yourself and others a favor, find some mufflers to put on that thing then work on jetting it properly.
                  De-stinking Penelope http://thegsresources.com/_forum/sho...d.php?t=179245

                  http://www.thegsresources.com/_forum...35#post1625535

                  Comment

                  • G.S.Joe

                    #10
                    Originally posted by tom203
                    The bike left factory with "headers" - something like you might put on a car that had a cheapo exhaust "manifold". But do you have mufflers attached to these headers? OOPs, I see your new post- no mufflers! This likely changes the jetting requirements- do you live in a noisy neighborhood?
                    I live in a place where I have satellite internet because nobody will run cable out to me, and my town's post office does not deliver my mail.

                    Unless the bears learn how to dial phone I'm not worried about anybody calling the cops.

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                    • G.S.Joe

                      #11
                      Originally posted by rustybronco
                      First, do yourself and others a favor, find some mufflers to put on that thing then work on jetting it properly.
                      I've been on the lookout for a decent price, but this is a budget-build unfortunately. I'm fine spending X dollars on the necessary stuff like gaskets/rebuild kits and anything else rubber. I was hoping to get away from spending $150+ for a used, rusted exhaust on a $500 bike unless I needed to. Is the scavenging thrown off that much? As I said, I'm still learning and have seen others with "good" running bikes with open headers as long as they're tuned properly, but maybe they're not running so "good" after all...

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                      • G.S.Joe

                        #12
                        Originally posted by allojohn
                        I run a 78 750 with K&N pods and V&H pipe. 15 pilot and 117.5 mains.

                        Those sound like huge mains. Does it run well for you? Plugs look good?

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                        • rustybronco
                          Forum LongTimer
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                          Past Site Supporter
                          • Jul 2005
                          • 14961
                          • Marysville, Michigan

                          #13
                          Originally posted by G.S.Joe
                          Those sound like huge mains. Does it run well for you? Plugs look good?
                          There not even close to being huge. The last Gs750 I jetted with pods and a 4-into 1 took 125.0's.
                          De-stinking Penelope http://thegsresources.com/_forum/sho...d.php?t=179245

                          http://www.thegsresources.com/_forum...35#post1625535

                          Comment

                          • tom203
                            Forum Guru
                            Past Site Supporter
                            • Aug 2010
                            • 8925
                            • Norway,Maine

                            #14
                            Originally posted by G.S.Joe
                            I live in a place where I have satellite internet because nobody will run cable out to me, and my town's post office does not deliver my mail.

                            Unless the bears learn how to dial phone I'm not worried about anybody calling the cops.
                            "satellite internet" both ways? I need to dump my cable service -what a ripoff!
                            Even in the boonies of Western Mass, you probably got harley riders and dealers to pamper them. Check CL for harley takeoff mufflers -the stock ones often get orphaned quick to enhance the ride. Typically, in my area, a set goes for about $50.
                            1981 gs650L

                            "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

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                            • tom203
                              Forum Guru
                              Past Site Supporter
                              • Aug 2010
                              • 8925
                              • Norway,Maine

                              #15
                              Muffler sets are getting cheaper all the time - why go deaf on your way to post office?

                              1981 gs650L

                              "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

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