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  4. DT 125 R '88... New project

DT 125 R '88... New project

Scheduled Pinned Locked Moved DTR
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  • J Offline
    J Offline
    jgr72
    wrote on last edited by
    #71

    @Calum Athena 170cc set fits well into this 3BN engine, there was no problem to install it. Original piston remain about 1-2mm below deck and dome comes just about up to deck hight. Athena piston comes to deck hight and the dome is smaller and comes just over the deck. Athena claims that compression ratio is 13.2 and that is also what I endup by calculating it... combustion chamber is about 13ml and 168cc devided by that is around 13. That's not actually the real CR, since 2T engines start to compress only after the channels in the barrel when piston comes up, damn I didn't measure that part of piston travel...

    Next step is to find better solution for TMX30... I ordered from ebay WR200 intake, let's see if it will line the carb better past the rear shock. If not, I may need to build up my own intake... At this point it seems that the DT230 Lanza boot was a waste of money, it does'nt seem to fit in any way... Anyone interested?

    I also ordered 170cc version exhaust from Romeu Henriques, let's see how it fits and feels... Silencer will be a gianelli alu silencer...

    Anyone have idea, where to start settings of that TMX30? 135 mainjet felt best last autumn... Maybe 140-150 mainjet and needle one step up?

    And for all that are oppressing me to keep this as original as possible, that's not happening now... I will store all original parts for later time if I feel to return this original back again...

    1 Reply Last reply
    1
    • CalumC Online
      CalumC Online
      Calum
      wrote on last edited by
      #72

      Sounds like you caught the tuning bug, very serious this is.

      I am surprised you needed a bigger inlet for such a small carb. You can get reducers to fit.

      Always Originate, Never Pirate!

      J 1 Reply Last reply
      0
      • CalumC Calum

        Sounds like you caught the tuning bug, very serious this is.

        I am surprised you needed a bigger inlet for such a small carb. You can get reducers to fit.

        J Offline
        J Offline
        jgr72
        wrote on last edited by jgr72
        #73

        @calum said in DT 125 R '88... New project:

        Sounds like you caught the tuning bug, very serious this is.

        I've had it since 1987 ๐Ÿ˜‰

        I am surprised you needed a bigger inlet for such a small carb. You can get reducers to fit.

        TMX30 will fit quite well to original joint, but the angle is bad... WR200 should have more horisontal angle to avoid rear shock and that joint is originally made for TMX30 carb.

        CalumC 1 Reply Last reply
        0
        • J jgr72

          @calum said in DT 125 R '88... New project:

          Sounds like you caught the tuning bug, very serious this is.

          I've had it since 1987 ๐Ÿ˜‰

          I am surprised you needed a bigger inlet for such a small carb. You can get reducers to fit.

          TMX30 will fit quite well to original joint, but the angle is bad... WR200 should have more horisontal angle to avoid rear shock and that joint is originally made for TMX30 carb.

          CalumC Online
          CalumC Online
          Calum
          wrote on last edited by
          #74

          @jgr72 So I'm running a Dellorto VHSA 32mm on stock inlet manifold with no issues.

          Always Originate, Never Pirate!

          Irongamer727I 1 Reply Last reply
          0
          • J Offline
            J Offline
            jgr72
            wrote on last edited by jgr72
            #75

            WR200 inlet did the trick I need:

            alt text

            Air filter barely misses the rear shock and frame...

            Now need to modify those inlet attachment bolt holes to make it fit into crankcase...

            Maybe I will loose some bottom torque due to the missing boost bottle!?

            CalumC 1 Reply Last reply
            2
            • J jgr72

              WR200 inlet did the trick I need:

              alt text

              Air filter barely misses the rear shock and frame...

              Now need to modify those inlet attachment bolt holes to make it fit into crankcase...

              Maybe I will loose some bottom torque due to the missing boost bottle!?

              CalumC Online
              CalumC Online
              Calum
              wrote on last edited by
              #76

              @jgr72 Personally I'd want to keep the boost bottle. Whether it actually does anything though as you say.

              They did have boost bottles on some WR models. I think it's more useful on road going bikes.

              Always Originate, Never Pirate!

              1 Reply Last reply
              0
              • J Offline
                J Offline
                jgr72
                wrote on last edited by
                #77

                Yeah, I'd like to have it too... It have been there for a reason... Okey, maybe I need to try to find such a WR inlet that have boost bottle! This bike will be used 99% on sand or asfalt roads...

                1 Reply Last reply
                0
                • J jgr72

                  About a week ago, I bought new project for me ๐Ÿ™‚ My plan and idea is to keep this as original looking as possible, and maybe try to get museum register for it. That's why I'd like to change exhaust to as original look as possible... maybe gianelli painted black!? Now bike is running quite well, and papers claim it has 17kw... I think I will just ride the next summer, and take it to parts during next winter...

                  here are few photos:

                  alt text

                  alt text

                  CalumC Online
                  CalumC Online
                  Calum
                  wrote on last edited by
                  #78

                  @jgr72 I'm sure it'll be fine, you went with the big bore kit and the way those boost bottles work is via harmonics. So it's doubtful the frequencies would have been correct anyway.

                  Always Originate, Never Pirate!

                  1 Reply Last reply
                  1
                  • J Offline
                    J Offline
                    jgr72
                    wrote on last edited by
                    #79

                    Hmm... that's true also... So if I want to use boost bottle, I need to enlarge it about 35% to be in the same as previously 125cc!

                    CalumC 1 Reply Last reply
                    0
                    • J jgr72

                      Hmm... that's true also... So if I want to use boost bottle, I need to enlarge it about 35% to be in the same as previously 125cc!

                      CalumC Online
                      CalumC Online
                      Calum
                      wrote on last edited by
                      #80

                      @jgr72 I think it's a little more complicated than that. As said it's all to do with Harmonics and the resonance frequency of the engine at a particular motion in the engines cycle.

                      I don't know the specifics in intimate details but the idea is this.

                      At some point in the engines RPM cycle, there is a dip in the air pressure and consequently the engine will perform less than optimally. They characterised this phenomena with a certain frequency. They then created a body with a natural frequency that matches the signature of this phenomena. When the engine hits this frequency, and is down on oxygen, the bottle resonates, forcing reserved air into the inlet tract. This makes up for the loss charge during this period and as a result performance is restored.

                      Now to my mind, there are so many factors that have to be considered that it's either pure genius or pure myth...it's hard to say whether the performance with or without is noticeable, it's probably so slight but the Japs just over engineer it all.

                      Always Originate, Never Pirate!

                      1 Reply Last reply
                      0
                      • CalumC Calum

                        @jgr72 So I'm running a Dellorto VHSA 32mm on stock inlet manifold with no issues.

                        Irongamer727I Offline
                        Irongamer727I Offline
                        Irongamer727
                        wrote on last edited by
                        #81

                        @calum was it really worth changing to a 32mm carb? I mean it's only a 4 mm difference from stock? Thought those 28mm mikuni carbs were well up for the job. I'm still running the 28mm with the 170 kit.

                        CalumC 1 Reply Last reply
                        0
                        • Irongamer727I Irongamer727

                          @calum was it really worth changing to a 32mm carb? I mean it's only a 4 mm difference from stock? Thought those 28mm mikuni carbs were well up for the job. I'm still running the 28mm with the 170 kit.

                          CalumC Online
                          CalumC Online
                          Calum
                          wrote on last edited by
                          #82

                          @irongamer727 It's not just the fueling, it's the amount of air you can get in as well. My brother ran a 38mm Keihin carb on his, although to be fair that was probablyt way too big. 32-34 is about right I'd say. The Aprilia RS125 ran 34 as standard and they were making 26-33bhp.

                          Always Originate, Never Pirate!

                          declanD 1 Reply Last reply
                          0
                          • CalumC Calum

                            @irongamer727 It's not just the fueling, it's the amount of air you can get in as well. My brother ran a 38mm Keihin carb on his, although to be fair that was probablyt way too big. 32-34 is about right I'd say. The Aprilia RS125 ran 34 as standard and they were making 26-33bhp.

                            declanD Offline
                            declanD Offline
                            declan
                            wrote on last edited by
                            #83

                            @calum are there any of the aprilia engines that donโ€™t have right hand drive?

                            CalumC 1 Reply Last reply
                            0
                            • declanD declan

                              @calum are there any of the aprilia engines that donโ€™t have right hand drive?

                              CalumC Online
                              CalumC Online
                              Calum
                              wrote on last edited by
                              #84

                              @declan Aprilia didn't make their engines. Just swap the swingarm when you do the engine. Simples.

                              Always Originate, Never Pirate!

                              declanD 1 Reply Last reply
                              0
                              • CalumC Calum

                                @declan Aprilia didn't make their engines. Just swap the swingarm when you do the engine. Simples.

                                declanD Offline
                                declanD Offline
                                declan
                                wrote on last edited by
                                #85

                                @calum well uno out of the Rotax engines but what if itโ€™s an sm

                                CalumC 1 Reply Last reply
                                0
                                • declanD declan

                                  @calum well uno out of the Rotax engines but what if itโ€™s an sm

                                  CalumC Online
                                  CalumC Online
                                  Calum
                                  wrote on last edited by
                                  #86

                                  @declan Just get an mx mate, much better bikes.

                                  Always Originate, Never Pirate!

                                  declanD 1 Reply Last reply
                                  0
                                  • CalumC Calum

                                    @declan Just get an mx mate, much better bikes.

                                    declanD Offline
                                    declanD Offline
                                    declan
                                    wrote on last edited by
                                    #87

                                    @calum ahh okay

                                    1 Reply Last reply
                                    0
                                    • J Offline
                                      J Offline
                                      jgr72
                                      wrote on last edited by
                                      #88

                                      Bike is getting ready for next summer:

                                      alt text

                                      That exhaust chamber :smiling_face_with_heart-eyes:

                                      alt text

                                      Gianelli silencer:

                                      alt text

                                      But need to twist something:

                                      alt text
                                      alt text

                                      I guess it's easier to warm and twist + cat a little bit of that exhaust chamber tail pipe... Gianelli's aluminium would melt away too easily...

                                      1 Reply Last reply
                                      0
                                      • CalumC Online
                                        CalumC Online
                                        Calum
                                        wrote on last edited by
                                        #89

                                        Looking lovely, I'd be reluctant to bend the pipe, just make up a larger bracket and move it closer.

                                        Always Originate, Never Pirate!

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