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DT125R FORUM

  1. Home
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  4. The pursuit for a brown sparkplug

The pursuit for a brown sparkplug

Scheduled Pinned Locked Moved Carburetor
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  • CalumC Offline
    CalumC Offline
    Calum
    wrote on last edited by
    #12

    You using the stock carb? Pretty sure they use a powerjet which should be the jet you want to be changing.

    Always Originate, Never Pirate!

    Irongamer727I 1 Reply Last reply
    0
    • CalumC Calum

      You using the stock carb? Pretty sure they use a powerjet which should be the jet you want to be changing.

      Irongamer727I Offline
      Irongamer727I Offline
      Irongamer727
      wrote on last edited by
      #13

      @calum yep there is a powerjet. I'll give the really big jets a try first. Because again, I've not heard anyone changing anything but the main jet.

      CalumC 1 Reply Last reply
      0
      • Irongamer727I Irongamer727

        @calum yep there is a powerjet. I'll give the really big jets a try first. Because again, I've not heard anyone changing anything but the main jet.

        CalumC Offline
        CalumC Offline
        Calum
        wrote on last edited by
        #14

        @irongamer727 So the powerjet kicks in at wide open throttle.

        You should be doing a plug chop at WOT.

        Therefore, changing the main jet won't affect the colour of the plug during a plug chop.

        Always Originate, Never Pirate!

        Irongamer727I 1 Reply Last reply
        0
        • D Offline
          D Offline
          DTR+NSR
          wrote on last edited by
          #15

          Pretty sure the power jet isn't changeable on these carbs.

          1 Reply Last reply
          0
          • CalumC Calum

            @irongamer727 So the powerjet kicks in at wide open throttle.

            You should be doing a plug chop at WOT.

            Therefore, changing the main jet won't affect the colour of the plug during a plug chop.

            Irongamer727I Offline
            Irongamer727I Offline
            Irongamer727
            wrote on last edited by
            #16

            @calum I'm currently going WOT sixth gear and turn ignition off. I can thereby see the plug colour at WOT. And it still looks a tad to white for my taste.

            1 Reply Last reply
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            • DartyD Offline
              DartyD Offline
              Darty
              wrote on last edited by Darty
              #17

              The Powerjet is a fixed system on the TM28,

              I used to run 340 Main, 30 Pilot, only because of extensivly modifing the Airbox volume,

              And, it was rubbish mostly.

              I had to replace my main body Carburettor gaskets because of symptoms near enough the same as you.

              I would recomend throughly checking for Air leaks as this is almost certainly your problem!

              Dont just throw fuel at this and hope for results.

              Work backwards.

              Keep it real

              Irongamer727I 1 Reply Last reply
              1
              • DartyD Darty

                The Powerjet is a fixed system on the TM28,

                I used to run 340 Main, 30 Pilot, only because of extensivly modifing the Airbox volume,

                And, it was rubbish mostly.

                I had to replace my main body Carburettor gaskets because of symptoms near enough the same as you.

                I would recomend throughly checking for Air leaks as this is almost certainly your problem!

                Dont just throw fuel at this and hope for results.

                Work backwards.

                Irongamer727I Offline
                Irongamer727I Offline
                Irongamer727
                wrote on last edited by
                #18

                @darty how would you check for Air leaks then?

                1 Reply Last reply
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                • Irongamer727I Offline
                  Irongamer727I Offline
                  Irongamer727
                  wrote on last edited by
                  #19

                  I do have the entire pice where the snorkel existed cut out. So there that as well.

                  DartyD 1 Reply Last reply
                  0
                  • Irongamer727I Irongamer727

                    I do have the entire pice where the snorkel existed cut out. So there that as well.

                    DartyD Offline
                    DartyD Offline
                    Darty
                    wrote on last edited by Darty
                    #20

                    @irongamer727 You donkey,

                    Why dont you try and restrict Air by patching up a section of the Airbox,

                    By doing so, i’ll bet a Roast dinner that it sorts out your lean condition.

                    I’ve played around alot with this, you’ll stuggle to fuel this properly with the TM28

                    Keep it real

                    Irongamer727I 1 Reply Last reply
                    1
                    • DartyD Darty

                      @irongamer727 You donkey,

                      Why dont you try and restrict Air by patching up a section of the Airbox,

                      By doing so, i’ll bet a Roast dinner that it sorts out your lean condition.

                      I’ve played around alot with this, you’ll stuggle to fuel this properly with the TM28

                      Irongamer727I Offline
                      Irongamer727I Offline
                      Irongamer727
                      wrote on last edited by
                      #21

                      @darty there isn't a good way of doing it, patching the Air box up I mean. In theory, I'll just get a slightly higher fuel consumption than "everyone else". From what I've understood the airbox is quite restrictive.

                      DartyD 1 Reply Last reply
                      0
                      • Irongamer727I Irongamer727

                        @darty there isn't a good way of doing it, patching the Air box up I mean. In theory, I'll just get a slightly higher fuel consumption than "everyone else". From what I've understood the airbox is quite restrictive.

                        DartyD Offline
                        DartyD Offline
                        Darty
                        wrote on last edited by
                        #22

                        @irongamer727 True, there are ways around it with Aluminum plate and bolts,

                        Basically, deal is, you cant complain if you dont see results without trying this first.

                        If you are determined, Start larger with a main, 350 - work backwards, its safer.

                        I personally dont recomend having the Airbox chopped completely.

                        Yes it's restrictive as standard, but otherwise you’ll see a significant drop in torque under 6k.

                        And without a larger carburettor, insignifcant Power gains at high RPMs without ignition timing adjustments.

                        Mostly bark, no bite

                        Keep it real

                        Irongamer727I 1 Reply Last reply
                        1
                        • DartyD Darty

                          @irongamer727 True, there are ways around it with Aluminum plate and bolts,

                          Basically, deal is, you cant complain if you dont see results without trying this first.

                          If you are determined, Start larger with a main, 350 - work backwards, its safer.

                          I personally dont recomend having the Airbox chopped completely.

                          Yes it's restrictive as standard, but otherwise you’ll see a significant drop in torque under 6k.

                          And without a larger carburettor, insignifcant Power gains at high RPMs without ignition timing adjustments.

                          Mostly bark, no bite

                          Irongamer727I Offline
                          Irongamer727I Offline
                          Irongamer727
                          wrote on last edited by
                          #23

                          @darty I've ordered 340-370 main now. Along with a more sensible pilot jet. Let's see how it turns out

                          1 Reply Last reply
                          0
                          • Irongamer727I Offline
                            Irongamer727I Offline
                            Irongamer727
                            wrote on last edited by
                            #24

                            https://imgur.com/gallery/wFEtwC6

                            Alright so I have now made a basic Air restrictor. As you know my DT is running slightly lean with a 320 main jet. Probably due to the fact that the airbox is cut open. I now installed the restrictor and for the first time ever she was running really rich.

                            What should I do?

                            A: Take out that stupid restrictor and upjet with the top cut out. (I know it's running lean)

                            B: Install the restrictor, maybe drill a couple of more holes, and downjet.

                            1 Reply Last reply
                            0
                            • CalumC Offline
                              CalumC Offline
                              Calum
                              wrote on last edited by
                              #25

                              Rejet the bike back down a tad.

                              Get it close to stock, then work from there.

                              Always Originate, Never Pirate!

                              Irongamer727I 1 Reply Last reply
                              0
                              • CalumC Calum

                                Rejet the bike back down a tad.

                                Get it close to stock, then work from there.

                                Irongamer727I Offline
                                Irongamer727I Offline
                                Irongamer727
                                wrote on last edited by
                                #26

                                @calum drill a couple of more holes or keep as it is?

                                CalumC 1 Reply Last reply
                                0
                                • Irongamer727I Irongamer727

                                  @calum drill a couple of more holes or keep as it is?

                                  CalumC Offline
                                  CalumC Offline
                                  Calum
                                  wrote on last edited by
                                  #27

                                  @irongamer727 What's your jetting. YOu said it was like 320.

                                  So just knock that down a tad.

                                  Always Originate, Never Pirate!

                                  Irongamer727I 1 Reply Last reply
                                  0
                                  • CalumC Calum

                                    @irongamer727 What's your jetting. YOu said it was like 320.

                                    So just knock that down a tad.

                                    Irongamer727I Offline
                                    Irongamer727I Offline
                                    Irongamer727
                                    wrote on last edited by
                                    #28

                                    @calum yes 320 now. But I don't want to loose power doing this.. some power decrease is acceptable..

                                    CalumC 1 Reply Last reply
                                    0
                                    • Irongamer727I Irongamer727

                                      @calum yes 320 now. But I don't want to loose power doing this.. some power decrease is acceptable..

                                      CalumC Offline
                                      CalumC Offline
                                      Calum
                                      wrote on last edited by
                                      #29

                                      @irongamer727 Yeah, you're not really getting the art of tuning...

                                      Bigger jets don't necessarily mean bigger power.

                                      The pathetic carb you're running is what is letting your engine down. You can only marry up so much oxygen with the fuel. More fuel doesn't mean more air as you simply are not flowing enough air. You need a bigger carb if you want to start chasing that power.

                                      Knocking the jet sizes down won't affect power unless A. You're dangerously lean, or you were already at that sweet spot.

                                      The optimal jetting would be to run the engine as lean as possible without incurring detonation. This would be indicated by the brown tan.

                                      Always Originate, Never Pirate!

                                      Irongamer727I 1 Reply Last reply
                                      0
                                      • CalumC Calum

                                        @irongamer727 Yeah, you're not really getting the art of tuning...

                                        Bigger jets don't necessarily mean bigger power.

                                        The pathetic carb you're running is what is letting your engine down. You can only marry up so much oxygen with the fuel. More fuel doesn't mean more air as you simply are not flowing enough air. You need a bigger carb if you want to start chasing that power.

                                        Knocking the jet sizes down won't affect power unless A. You're dangerously lean, or you were already at that sweet spot.

                                        The optimal jetting would be to run the engine as lean as possible without incurring detonation. This would be indicated by the brown tan.

                                        Irongamer727I Offline
                                        Irongamer727I Offline
                                        Irongamer727
                                        wrote on last edited by
                                        #30

                                        @calum do you think there will be a big difference in fuel consumption with a 350 jet and let's say 260?

                                        CalumC 1 Reply Last reply
                                        0
                                        • Irongamer727I Irongamer727

                                          @calum do you think there will be a big difference in fuel consumption with a 350 jet and let's say 260?

                                          CalumC Offline
                                          CalumC Offline
                                          Calum
                                          wrote on last edited by
                                          #31

                                          @irongamer727 not drastic. I would exect significant consumption in incorrect jetting due to poor pwower delivery and optimised combustion losses. Also an increase in carb sizes will result in losses.

                                          Always Originate, Never Pirate!

                                          Irongamer727I 1 Reply Last reply
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