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Rejetting:what to do? where to go?

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  • Rejetting:what to do? where to go?

    I just got a new pipe thats straight through, its popping a little bit im worried that since theres no back pressure, its running a bit lean on air and thus heating up abit more.

    So ive been advised to do 100/100 with rejet from the stock 92.5/95

    Anyone have any idea how much this involves in terms of mulla?

    I dont want to do this mod for perfomance sake, but rather allow more fuel in so that the engine doesnt overheat. Is it really something i should worry about with a 250 due to lower compression not making much of a difference anyway?


    I know jack about carbs, so any insight would be appreciated

    thanks


  • #2
    Whilst i don't have an answer for you - i think you'll find that the compression on your 250 is likely higher than most thous - at least most thous from more than 2-3 years ago or more - i know GPX250s are up near 12.5:1... which is higher than my 600rr (12.2:1) ...
    “Crashing is shit for you, shit for the bike, shit for the mechanics and shit for the set-up,” Checa told me a while back. “It’s a signal that you are heading in the wrong direction. You want to win but crashing is the opposite. It’s like being in France when you want to go to England and when you crash you go to Spain. That way you’ll never get to England!” -- Carlos Checa

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    • #3
      The main reason you want to rejet is because if its to lean it will eventually burn a hole in your cylinder .

      it happened to someones cbr250 on here i can't remember who tho.

      a little rich is ok
      but lean is bad and expensive
      Wes

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      • #4
        I would have suggested to go see Russell @ Dynotime in Wangara but I hear that unfortunately he doesn't do tuning on carbs anymore and I don't think he does 250s either anyway.

        The best suggestion would be to find a guide on the net and have a crack at it yourself.

        "At the start of the season, you can’t win the championship in the first round, but you can lose it.” - Travis Pastrana

        "If your mind can conceive it then
        your hands can achieve it"- Nigel Petrie (Engineeredtoslide.com)

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        • #5
          The carb needle sits in the jet. The jet size determines how much fuel is let into the carb to be burned.

          Increasing the jet size will allow the engine to run richer which will hopefully cure your backfiring problems.

          Jets are around 20-30 $ a pop and it might take a few hours of playing around to get the adjustment just right

          edit: Yes it is something to worry about, the bike will perform much better with a larger set of jets after the new exhaust as long as it can also pull in more air.

          Any dealer will be able to sort out the jets for you if you are unwilling to do them yourself (lots of guides on the net). Probably cost a few hours in labour
          Last edited by taint; 10-11-2007, 07:07 AM.

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          • #6
            If you go to the factory pro website they have a thing about tuning carbs

            Factory Pro: Producers of the EC997 Low Inertia Eddy Current Dynamometer Series and Quality MC performance products

            then go to product support at the top of the page

            click on CV carb tuning (assuming you have these which you probably will)

            high RPM engines

            then you get a guide on how to adjust your carbs correctly.
            Wes

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            • #7
              What bike is it?

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              • #8
                Jets cost fuck all, get several different sizes. Run the bike up and do plug chops to determine if the motor is running to lean or rich.
                I love two strokes. Because they annoy the shit out of people. ^_^

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                • #9
                  Yeah, I'd say $5 a pop per jet is more realistic.

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                  • #10
                    Try richening up the midrange by placing a shim under the needle in the carbs.

                    You can generally richen up the low range with the mixture screws.

                    If that works ok you can just buy the mains.

                    But with the US sollar so shit it really dosen't cost that much to buy a jet kit from Factry Pro or Eaby
                    You put the c*nt in country run

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                    • #11
                      Originally posted by likefry View Post
                      If you go to the factory pro website they have a thing about tuning carbs
                      From memory when I got my Factory Pro jet kit for my CBR900 it also had a pretty comprehensive guide on the install of the kit and different settings dependent on what mods you already had on the bike. When Russell @ Dynotime fitted it he said he used the base settings on the guide that was provided and it was spot on when he ran it on the dyno (i.e. air/fuel mixtures were exactly how they should be, not too lean, not too rich all the way through the rev range).

                      The kits tend to come with a range of jets (mains and secondaries), a new set of needles, slide springs, float bowl screws and the tool to remove/screw in the jets:


                      "At the start of the season, you can’t win the championship in the first round, but you can lose it.” - Travis Pastrana

                      "If your mind can conceive it then
                      your hands can achieve it"- Nigel Petrie (Engineeredtoslide.com)

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                      • #12
                        thanks for the input

                        some further info:

                        1. its a hyosung 250 so its a twin
                        2. I'm not mechanically minded and would rather let a professional who knows what theyre doing to handle it. Although i am willing to learn with a little bit of guidence
                        3. Not sure if any kits exist, All i know is that they are mikuni.

                        So where should i go from here?

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                        • #13
                          I think if you just pour the fuel down the carby throats that you will get better metering than from your Hyo carbs

                          Tried looking for a Dynojet kit?

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                          • #14
                            Originally posted by Desmogod View Post
                            I think if you just pour the fuel down the carby throats that you will get better metering than from your Hyo carbs

                            Tried looking for a Dynojet kit?

                            haha, cruel.

                            The shop you bought it (dale britton?) should be able to sort you out with a jetting kit and fit it. Give em a buzz and grab a price

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                            • #15
                              maybe try rilusi?..

                              got my vtr250 jetted the other day cos it was running a bit lean..

                              set me back $250 all up for dyno, jetting and then re-dynoed.

                              now it lets rip a whopping 25.65hp

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