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DT125R FORUM

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  3. What is causing my bike to overheat?

What is causing my bike to overheat?

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  • D DTR2003

    Ok, thanks for pointing me in the right direction.
    I'm not very knowledgable about motorbikes, but I have a friend coming to help me at the weekend.

    I'm not sure what I should do about the jets, because I don't think the exhaust is standard.

    The previous owner must have changed the jets with the exhaust because it had a 240 main jet in, when the manual says to use a 210 main jet.

    Should I buy the original yamaha exhaust so I can get the jetting exactly how the manual says?

    I'm sorry if this is confusing
    Do you mind if I come back at the weekend and ask a few more questions when I have more details?

    Thanks for the help, I really appreciate it.

    declanD Offline
    declanD Offline
    declan
    wrote on last edited by
    #4

    @dtr2003 ask away, main things to check in my opinion is the fixing make sure everything that is anything to do with the carb is “air tight” what main jet is in the new carb? I’d put the one out of the leaking one in it and that should be your jetting just about done and no don’t buy a standard exhaust that’s just not necessary

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    • D Offline
      D Offline
      DTR2003
      wrote on last edited by
      #5

      Ok guys, You've been a big help,

      The new carb has a 240 main jet too I think, but I'm not certain.
      Should I put a 210 in?

      I'll take off the carb at the weekend, double-check the jets, float height, and look for any leaks and adjust the screws on the carb.

      Thanks

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      • CalumC Offline
        CalumC Offline
        Calum
        wrote on last edited by
        #6

        Ask away, but I'd be very surprised if the suggested comments are you problem.

        The bike would run hot if it was lean, but usually it creates death ash, under load and kills the engine.

        In my experience, I would not ride the bike until you've got this problem nailed.

        I would check first to ensure there is no air leaks, and that you do indeed have coolant. A working thermostat and all the fluids are there as expected.

        Always Originate, Never Pirate!

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        • O Offline
          O Offline
          oldman
          wrote on last edited by
          #7

          also check operation of water pump, when warmed up and thermostat open you will see turbulence with the RAD cap off, take it off prior to warming bike though as pressure could be present if you don't. Put my 88 bike right back to standard with 210 main jet and standard exhaust, Calum is far more knowledgeable than me on the carbs so agree air leak or similar could well be making your bike super lean but need to check what's the setup of your new carb. If you confirm all is well with that rules a lot out. Good luck!

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          • CalumC Offline
            CalumC Offline
            Calum
            wrote on last edited by
            #8

            Yeah I'm not saying it's not fueling, but if the bike was so lean to cause the coolant to rise, then the affects to your engine are going to be horrendous.

            Usually, when running lean, preignition or detonation occurs. Both of which are engine killers.

            They tend to happen under load when the fueling is lean causing the combustible mix to preignite before the designated ignition point. Hammering the engine internals to pieces.

            It's so bad for the engine that if this were the case, I'd be looking to whip the cylinder off and check the tolerances.

            But as said, these things happen under load, and I know you've tried riding it (DON'T) but seriously the engine would destroy itself pretty quickly if it was that lean.

            So, what are you left with. Well the other thing is the coolant system is naff. Probably more likely, however the bike wouldn't be so bad to run, especially when cold. And it would take a bit of time before it became a noticeable problem.

            So it sounds to me like there are multiple issues here, possibly carburetor related, but does sound coolant related.

            I'll have a think.

            Always Originate, Never Pirate!

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            • F Offline
              F Offline
              finnerz89
              wrote on last edited by
              #9

              210 is the main jet size for later bikes, RE/X models
              240 main jet is the earlier ones I believe, same carb though. Doesn't explain your lean running issue though

              Current bikes:
              DT125X '07
              Street Triple R '11
              Aprilia ETV1000 '02

              Previous:
              DR650RSE '96
              FJ1200 '92

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              • CalumC Offline
                CalumC Offline
                Calum
                wrote on last edited by
                #10

                Main jet only really controls the fuelling at wide open throttle. The needle is going to restrict flow at the other times.

                As pointed out, this isn't strictly true, but it can be used in this example when at no load

                Always Originate, Never Pirate!

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                • CalumC Calum

                  Main jet only really controls the fuelling at wide open throttle. The needle is going to restrict flow at the other times.

                  As pointed out, this isn't strictly true, but it can be used in this example when at no load

                  F Offline
                  F Offline
                  finnerz89
                  wrote on last edited by
                  #11

                  @calum yeah I know, just pointing out the differences. It's also worth noting that the later carbs have 2 positions for the needle clip whereas the early ones have more.

                  Current bikes:
                  DT125X '07
                  Street Triple R '11
                  Aprilia ETV1000 '02

                  Previous:
                  DR650RSE '96
                  FJ1200 '92

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                  • terry.tzT Offline
                    terry.tzT Offline
                    terry.tz
                    wrote on last edited by terry.tz
                    #12

                    guy's slow down you all made some good points here but its a lot of opinions and the guys, not a DTR fanatic or bike mechanic so calm down personally I wouldn't do anything till I checked the coolant level as there could have been air in the system from changing the carb
                    next the plug to see if that shows me its lean
                    but if the bike is ticking over ok like it's not fluctuating revs that much but when revved a bit it takes awhile to return
                    or it climbs revs when ticking over then ye its most probably lean
                    and like @Calum said don't be riding it as you might not have a bike for long if you do

                    pictures and videos make it easier for people to see and hear the problem to help you so if you can get some up bud

                    "Muddy water is best cleared by leaving it alone" Alan Watts

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                    • D Offline
                      D Offline
                      DTR2003
                      wrote on last edited by
                      #13

                      You guys have given me a lot to work with...

                      No, I definitely won't be riding it anywhere when it's running like this.

                      I'll print off this whole thread and show it to my friend who knows a lot more about bikes than me...

                      Thanks

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