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DT125R FORUM

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inlet 38mm

Scheduled Pinned Locked Moved Tuning
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  • Glynn123G Glynn123

    A little off topic but what are you looking to achieve with a 38mm carb? It’s massively oversized for standard porting, I would be looking at more 30-32mm maximum

    DylanDT219D Offline
    DylanDT219D Offline
    DylanDT219
    wrote on last edited by
    #16

    @glynn123
    I have a 170cc Athena that does not even do 100 km / h in addition to the fact that now we have elaborated the cylinder by opening the 38mm ports more I think it is a must

    1 Reply Last reply
    0
    • CalumC Calum

      @glynn123 I can't say that this DTR ran particularly well.

      It DRANK fuel it was totally overkill and you'd probably have gotten better performance out of a smaller carb. It was 170cc mind.

      DylanDT219D Offline
      DylanDT219D Offline
      DylanDT219
      wrote on last edited by
      #17

      @calum
      mhm I'm not particularly sure if a 38mm is too excessive, but as soon as I mount it I'll try it and I'll let you know

      CalumC 1 Reply Last reply
      0
      • DylanDT219D DylanDT219

        @calum
        mhm I'm not particularly sure if a 38mm is too excessive, but as soon as I mount it I'll try it and I'll let you know

        CalumC Offline
        CalumC Offline
        Calum
        wrote on last edited by
        #18

        @DylanDT219 the ports aren't the problem with the Athena kit. They aren't great but they aren't the problem. I will be writing a blog on this in the fullness of time, along with how you fix the Athena barrel and what it is like afterwards. But it's all in development now.

        In short, it's the port timings not the port windows that are the problem.

        Take the head off, or look up the exhaust port and rotate the crankshaft 360 degrees to see what I mean. It should be obvious.

        Also bigger is not always better. The engine produces a finjte amount of vacuum pressure. A bigger carb reaults in losses of this oreasure. Loss of pressure results in loss of soeed which will negatively impact your performance. Don't go too big. Don't go too small. There is a middle ground. 34 is probably a little on the big side. 32mm is pretty sweet.

        Always Originate, Never Pirate!

        DylanDT219D 1 Reply Last reply
        0
        • CalumC Calum

          @DylanDT219 the ports aren't the problem with the Athena kit. They aren't great but they aren't the problem. I will be writing a blog on this in the fullness of time, along with how you fix the Athena barrel and what it is like afterwards. But it's all in development now.

          In short, it's the port timings not the port windows that are the problem.

          Take the head off, or look up the exhaust port and rotate the crankshaft 360 degrees to see what I mean. It should be obvious.

          Also bigger is not always better. The engine produces a finjte amount of vacuum pressure. A bigger carb reaults in losses of this oreasure. Loss of pressure results in loss of soeed which will negatively impact your performance. Don't go too big. Don't go too small. There is a middle ground. 34 is probably a little on the big side. 32mm is pretty sweet.

          DylanDT219D Offline
          DylanDT219D Offline
          DylanDT219
          wrote on last edited by
          #19

          @calum

          look maybe because here we have a different mechanics thought but put a 38mm on a 170cc athena which also has some design problems I don't see a problem in doing so, I repeat my dtr with the 170cc athena, carb of the 30mm, firebox + fmf and not it is not even 100 km / h. I prepared the cylinder together with a friend of mine who knows enough and we also prepared the engine block along with everything a zeltronic control unit, reed valve v-force 4 will also be added. I think a 32mm with all these things is underdeveloped for the components it will mount

          1 Reply Last reply
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          • CalumC Offline
            CalumC Offline
            Calum
            wrote on last edited by
            #20

            Right, okay cool. I am just trying to help.

            I have been around these bikes for 13 years. I have seen how they tune. I have ran Athena 170 with 38mm carb and rode it daily. I linked a video of that bike on a flyby.

            I am trying to give you my experience. Out of all the modifications I have done, the best I have got out of my bike is a ported 3mb with altered squish 32mm carb, underslung pipe and zeel.

            alt text

            It's not the carb as to why you can't do over 100

            Always Originate, Never Pirate!

            DylanDT219D 1 Reply Last reply
            1
            • CalumC Calum

              Right, okay cool. I am just trying to help.

              I have been around these bikes for 13 years. I have seen how they tune. I have ran Athena 170 with 38mm carb and rode it daily. I linked a video of that bike on a flyby.

              I am trying to give you my experience. Out of all the modifications I have done, the best I have got out of my bike is a ported 3mb with altered squish 32mm carb, underslung pipe and zeel.

              alt text

              It's not the carb as to why you can't do over 100

              DylanDT219D Offline
              DylanDT219D Offline
              DylanDT219
              wrote on last edited by
              #21

              @calum
              go easy I'm not saying you don't know anything about it but here it works differently, especially because I live in Switzerland and here. engine blocks of the dt are different from all the rest of the world such as the 4BL there has never been here etc. etc. my engine block is 3ME and since you have worked a lot on this type of bike you will also know this and you will also know that they are blocked , for sure the carburettor is not the problem but it can help a lot

              Glynn123G 1 Reply Last reply
              0
              • DylanDT219D DylanDT219

                @calum
                go easy I'm not saying you don't know anything about it but here it works differently, especially because I live in Switzerland and here. engine blocks of the dt are different from all the rest of the world such as the 4BL there has never been here etc. etc. my engine block is 3ME and since you have worked a lot on this type of bike you will also know this and you will also know that they are blocked , for sure the carburettor is not the problem but it can help a lot

                Glynn123G Offline
                Glynn123G Offline
                Glynn123
                wrote on last edited by
                #22

                @dylandt219 Calum’s right I’m afraid, carburettor is not the issue..
                I’ve played around with the ignition timing through Ignitech DCCDIP2 aswell as carburettor and all sorts on my DT through the years. I recommend you work through what you’ve done and find the actual issue or limitation that’s holding the bike back, as even the standard 28mm can quite easily produce numbers on a mild ported 170 kit. If you’ve been messing with your timing through the zeeltronic put it back to a base map, fresh spark plug and check the spark is good, these units have had issues in the past and it’s not unknown for them to be duff out the factory. I would be more inclined to suggest an exhaust issue or timing related/spark problem than anything else, or if you’re still using the servo powered YPVS make sure you’ve not got it running backwards!
                The carburettor should not be an issue unless you have jetted it absolutely wrong, but I think if that was the case you’d be having terrible running conditions all the time.

                CalumC DylanDT219D 2 Replies Last reply
                2
                • Glynn123G Glynn123

                  @dylandt219 Calum’s right I’m afraid, carburettor is not the issue..
                  I’ve played around with the ignition timing through Ignitech DCCDIP2 aswell as carburettor and all sorts on my DT through the years. I recommend you work through what you’ve done and find the actual issue or limitation that’s holding the bike back, as even the standard 28mm can quite easily produce numbers on a mild ported 170 kit. If you’ve been messing with your timing through the zeeltronic put it back to a base map, fresh spark plug and check the spark is good, these units have had issues in the past and it’s not unknown for them to be duff out the factory. I would be more inclined to suggest an exhaust issue or timing related/spark problem than anything else, or if you’re still using the servo powered YPVS make sure you’ve not got it running backwards!
                  The carburettor should not be an issue unless you have jetted it absolutely wrong, but I think if that was the case you’d be having terrible running conditions all the time.

                  CalumC Offline
                  CalumC Offline
                  Calum
                  wrote on last edited by
                  #23

                  @glynn123 It sounds like Powervalve, gearing, or other issue.

                  100KMH is attainable on stock restricted DTR.

                  Always Originate, Never Pirate!

                  DylanDT219D 1 Reply Last reply
                  0
                  • Glynn123G Glynn123

                    @dylandt219 Calum’s right I’m afraid, carburettor is not the issue..
                    I’ve played around with the ignition timing through Ignitech DCCDIP2 aswell as carburettor and all sorts on my DT through the years. I recommend you work through what you’ve done and find the actual issue or limitation that’s holding the bike back, as even the standard 28mm can quite easily produce numbers on a mild ported 170 kit. If you’ve been messing with your timing through the zeeltronic put it back to a base map, fresh spark plug and check the spark is good, these units have had issues in the past and it’s not unknown for them to be duff out the factory. I would be more inclined to suggest an exhaust issue or timing related/spark problem than anything else, or if you’re still using the servo powered YPVS make sure you’ve not got it running backwards!
                    The carburettor should not be an issue unless you have jetted it absolutely wrong, but I think if that was the case you’d be having terrible running conditions all the time.

                    DylanDT219D Offline
                    DylanDT219D Offline
                    DylanDT219
                    wrote on last edited by
                    #24

                    @glynn123
                    no I understood that the problem is not the carburetor but I repeat it is one thing that helps the motorcycle to do some numbers for sure, mine has been blocked at the level of the control unit in fact as I repeat I will command the zeltronic

                    1 Reply Last reply
                    0
                    • CalumC Calum

                      @glynn123 It sounds like Powervalve, gearing, or other issue.

                      100KMH is attainable on stock restricted DTR.

                      DylanDT219D Offline
                      DylanDT219D Offline
                      DylanDT219
                      wrote on last edited by
                      #25

                      @calum
                      the problem is that it does not even do 100 km / h reaches a maximum of 85-90

                      1 Reply Last reply
                      0
                      • CalumC Offline
                        CalumC Offline
                        Calum
                        wrote on last edited by
                        #26

                        @DylanDT219 I'll just clarify this one more time.

                        It's not the size of the carb as the reason why you can't do 100KMH. A stock DTR will do that no problems.

                        The problem lies elsewhere.

                        As I initially said, 38mm can be attained on the stock inlet manifold if you enlarge the size of the inlet manifold.

                        I used a drill attachment called a "Hole Saw". It was a crude method that worked.

                        Whilst YES it can be done, you won't net gains from a bigger carb. Bigger is not always better.

                        I won't say anymore on it now.

                        Always Originate, Never Pirate!

                        T 1 Reply Last reply
                        0
                        • CalumC Calum

                          @DylanDT219 I'll just clarify this one more time.

                          It's not the size of the carb as the reason why you can't do 100KMH. A stock DTR will do that no problems.

                          The problem lies elsewhere.

                          As I initially said, 38mm can be attained on the stock inlet manifold if you enlarge the size of the inlet manifold.

                          I used a drill attachment called a "Hole Saw". It was a crude method that worked.

                          Whilst YES it can be done, you won't net gains from a bigger carb. Bigger is not always better.

                          I won't say anymore on it now.

                          T Offline
                          T Offline
                          theportingmaster
                          wrote on last edited by
                          #27

                          @calum The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone...(while it benefits from porting, lifting the whole lot 3mm is a bad idea) The Athena 170 cylinder is exactly the same casting as the 125, but bored out more and the pv is spaced further away from the bore. double check the pv cable setting. On mine with the pulley lined up with the mark, it was only about 3/4 open. Only when I looked up the port did I spot why it felt so flat initially! Exhaust port width limit is 73% of the bore diameter with good rings (measured straight across). So 56mm bore is 41mm and the 65mm bore can be opened up to 47mm. Although in the interests of safety I've stuck with 45mm for now (70%), same as the standard RD350. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so it has 125cc sized ports. I opened them up to 170cc sized ports by widening the exhaust 5mm, and lifting the transfers about 1mm.
                          Initially the 170 kit felt awful, until I double checked the pv setting and found the spool must have a different end for DT's, as even with the pulley lined up, it was about 3mm closed. Once that was reset, it flew... Mick Abbey said 30mm best carb
                          for ported 170 so fitted 30mm Koso-Pwk.

                          CalumC 1 Reply Last reply
                          1
                          • T theportingmaster

                            @calum The first people with a 170 kit lifted the cylinder 3mm, hence the terrible torque curve..but from then on the myth that the 170 kit needed 'port adjustment' was set in stone...(while it benefits from porting, lifting the whole lot 3mm is a bad idea) The Athena 170 cylinder is exactly the same casting as the 125, but bored out more and the pv is spaced further away from the bore. double check the pv cable setting. On mine with the pulley lined up with the mark, it was only about 3/4 open. Only when I looked up the port did I spot why it felt so flat initially! Exhaust port width limit is 73% of the bore diameter with good rings (measured straight across). So 56mm bore is 41mm and the 65mm bore can be opened up to 47mm. Although in the interests of safety I've stuck with 45mm for now (70%), same as the standard RD350. Most people reported a good increase in bottom end grunt but no real gain at peak hp. It turns out this is mainly due to the cylinder casting being the same as their 125cc cylinder, so it has 125cc sized ports. I opened them up to 170cc sized ports by widening the exhaust 5mm, and lifting the transfers about 1mm.
                            Initially the 170 kit felt awful, until I double checked the pv setting and found the spool must have a different end for DT's, as even with the pulley lined up, it was about 3mm closed. Once that was reset, it flew... Mick Abbey said 30mm best carb
                            for ported 170 so fitted 30mm Koso-Pwk.

                            CalumC Offline
                            CalumC Offline
                            Calum
                            wrote on last edited by Calum
                            #28

                            @theportingmaster At bottom dead centre, the exhaust port is still covered by the piston. The same goes for the transfers too.

                            https://www.youtube.com/watch?v=e6dc-5hFH5w

                            Lifting the barrel up so the exhaust/transfer ports are actually exposed will allow the engine to reach its full potential.

                            Not to mention the actual transfer ports aren't fantastic.

                            Here's my DT 125 R 3MB00P Barrel
                            alt text

                            vs the Athena 170

                            alt text

                            For fun let's compare that against a bog standard Aprilia RS 125 barrel

                            alt text

                            The DT just isn't a fast bike. But a "Performance" barrel that covers the transfer ports and exhaust port at bottom dead centre isn't helping matters.

                            Always Originate, Never Pirate!

                            DylanDT219D 1 Reply Last reply
                            0
                            • CalumC Calum

                              @theportingmaster At bottom dead centre, the exhaust port is still covered by the piston. The same goes for the transfers too.

                              https://www.youtube.com/watch?v=e6dc-5hFH5w

                              Lifting the barrel up so the exhaust/transfer ports are actually exposed will allow the engine to reach its full potential.

                              Not to mention the actual transfer ports aren't fantastic.

                              Here's my DT 125 R 3MB00P Barrel
                              alt text

                              vs the Athena 170

                              alt text

                              For fun let's compare that against a bog standard Aprilia RS 125 barrel

                              alt text

                              The DT just isn't a fast bike. But a "Performance" barrel that covers the transfer ports and exhaust port at bottom dead centre isn't helping matters.

                              DylanDT219D Offline
                              DylanDT219D Offline
                              DylanDT219
                              wrote on last edited by
                              #29

                              @calum
                              Mhm

                              Glynn123G 1 Reply Last reply
                              0
                              • DylanDT219D DylanDT219

                                @calum
                                Mhm

                                Glynn123G Offline
                                Glynn123G Offline
                                Glynn123
                                wrote on last edited by
                                #30

                                @dylandt219 asking for advice and replying in the way you have is childish and just makes you look like a tool mate, if you clearly don’t understand what you are doing I think the best advice anyone can give you now is take the bike to a mechanic. Everyone here is trying to be helpful but it’s clear you’ve already chosen the route you want to go down, so why even ask?
                                You can take the advice or alternatively spend £200+ on a big carb and have an even bigger steaming pile of shite that still goes 100km/h, you’ll learn either way

                                CalumC DylanDT219D 2 Replies Last reply
                                0
                                • Glynn123G Glynn123

                                  @dylandt219 asking for advice and replying in the way you have is childish and just makes you look like a tool mate, if you clearly don’t understand what you are doing I think the best advice anyone can give you now is take the bike to a mechanic. Everyone here is trying to be helpful but it’s clear you’ve already chosen the route you want to go down, so why even ask?
                                  You can take the advice or alternatively spend £200+ on a big carb and have an even bigger steaming pile of shite that still goes 100km/h, you’ll learn either way

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

                                  @glynn123 🤣

                                  So what I consider the "Holy Bible" for two stroke tuning
                                  Graham Bell's Two Stroke Performance Tuning. I've read it cover to cover, is a real eye opener.

                                  Some of the things just seem quite obvious now, but the part about carb size was really interesting.

                                  Always Originate, Never Pirate!

                                  1 Reply Last reply
                                  1
                                  • Glynn123G Glynn123

                                    @dylandt219 asking for advice and replying in the way you have is childish and just makes you look like a tool mate, if you clearly don’t understand what you are doing I think the best advice anyone can give you now is take the bike to a mechanic. Everyone here is trying to be helpful but it’s clear you’ve already chosen the route you want to go down, so why even ask?
                                    You can take the advice or alternatively spend £200+ on a big carb and have an even bigger steaming pile of shite that still goes 100km/h, you’ll learn either way

                                    DylanDT219D Offline
                                    DylanDT219D Offline
                                    DylanDT219
                                    wrote on last edited by
                                    #32

                                    @glynn123

                                    I wonder why I heat up so much ... in any case I repeat for the 8493020'39494598292 time since here you probably can't understand that I KNOW VERY WELL THAT A CARBURETTOR DOES NOT SOLVE MY PROBLEM but I know and help I can give to bike more than everything I'm doing, so let's open these eyes and read more, thanks 🙂

                                    1 Reply Last reply
                                    0
                                    • CalumC Offline
                                      CalumC Offline
                                      Calum
                                      wrote on last edited by
                                      #33

                                      For completeness

                                      alt text

                                      This is my old inlet manifold that I opened up to easily accept larger carbs.

                                      Always Originate, Never Pirate!

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