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Carby adjustment screws-help please?

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  • Carby adjustment screws-help please?

    Ok, I bought the kids (cough) a cheap chinese type 50cc dirt bike, assembled it (properly, with grease, Loctite and cable ties lol) with no instructions, starting guide shows throttle cable adjustment (done) and idle/mixture screws.
    Now, the idle I get (has a spring behind it), but bike will only run with the choke on. The choke has 3 positions (on, half and closed), can just about get it to run on half choke, runs fine on full choke, but absolutely refuses to run on closed choke, in fact it stalls out (sounds like flooding, a wet fart noise) if you hold open revs from open choke and close it. So, my first guess is mixture, which I believe to be the second screw next to the idle. So, question is when I screw it inwards (tighten or clockwise) am I richening or leaning? Does screw in increase fuel or decrease fuel?
    Also, what are tell-tale signs of lean or rich running? I am assuming it is rich and flooding when choke closed, but there is no smell of unburnt fuel or crackle crackle of a lean burn off throttle?
    Confused...

    Any ideas? (besides the burn it coz it's shit lol)

    Cheers

    sS
    yes, i am ignorant
    yes, i am a prick
    no, i don't care
    you make me sick

  • #2
    First get the terminology right...

    The choke is closed when you start a cold bike, then when it warms up you open the choke...

    You seem to be saying confusing things...

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    • #3
      Have you looked to see the choke is operating the way you think it is?

      As in when you think the choke is closed on the operating lever, blocking the carby bore, that it actually is?

      Comment


      • #4
        I screw in until idle starts to limp then back put a quarter turn. This gives the leanest practicable idle.
        -

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        • #5
          One and a half turns out seems popular from memory.
          -

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          • #6
            so just making sure.. burning, is off of the table?

            And its a 4stroke yeah?
            You can't *burrrp* can't just post, just post anything you feel like morty, you just *burrp* just end up *burrp* end up hurting people's feelings morty I mean how, how would you like it if I said things that offended you morty?

            Comment


            • #7
              Originally posted by shortSteve View Post
              Ok, I bought the kids a cheap chinese type 50cc dirt bike
              Private health cover?

              Comment


              • #8
                Check the float level. Might be to low if it will start/run with the choke.
                any mixture adjustment externally will be for idle adjustment.
                running more than idle will be controlled by the main jet and needle in a 2 stroke.
                4 stroke will be similar.
                Id pull the carb down and give it a clean. Blow out the jets and reassemble.
                wouldnt be the first time some petrol has sat at the bottom of the bowl and clogged jets as it will evaporate and leave a horrible white shit in there to stuff things.

                Comment


                • #9
                  Originally posted by Desmo View Post
                  Private health cover?
                  Yep, TPD and death, aswell as income protection. Should cover theusual dramas lol.

                  It's a 4 stroke, new. Carb looked clean when I put on the air filter.
                  Carby definately sounds "sucky" as I close the choke button, so [MENTION=6669]Rich...[/MENTION] 's definition is probably more correct.
                  Hmm. Float levels eh? Better get googling
                  yes, i am ignorant
                  yes, i am a prick
                  no, i don't care
                  you make me sick

                  Comment


                  • #10
                    Lol missus flys over east, buys his girls a mini dirtbike
                    B19 Oakford V.B.F.S

                    Comment


                    • #11
                      Originally posted by shortSteve View Post
                      Yep, TPD and death, aswell as income protection. Should cover theusual dramas lol.

                      It's a 4 stroke, new. Carb looked clean when I put on the air filter.
                      Carby definately sounds "sucky" as I close the choke button, so Rich... 's definition is probably more correct.
                      Hmm. Float levels eh? Better get googling
                      So it's got a button you lift?

                      Comment


                      • #12
                        Carby adjustment screws-help please?

                        The idle screw; what side of the carb is it on, engine or airfilter?
                        In sterquiliniis invenitur.

                        Comment


                        • #13
                          Signs of running rich: black smoke, fuel smell, boggy a bit like it is running on choke (if really rich), doughy throttle response, black/wet plugs
                          Signs of running lean: high idle, reluctance to return to idle, hot exhaust, melty plugs, pinging, bogging under load, but engine wants to rev un-loaded
                          “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

                          Comment


                          • #14
                            Originally posted by thro View Post
                            Signs of running rich: black smoke, fuel smell, boggy a bit like it is running on choke (if really rich), doughy throttle response, black/wet plugs
                            Signs of running lean: high idle, reluctance to return to idle, hot exhaust, melty plugs, bogging under load, but engine wants to rev un-loaded
                            This isn't entirely true. An engine that runs rich is pretty hard to diagnose without a wideband O2 sensor and will have hardly any smell, an exhaust that smells is more than likely running lean and you are smelling unburnt hydrocarbons.
                            But yes, black smoke is WAY too rich...

                            Comment


                            • #15
                              Depends how rich we're talking

                              But yeah, taking a look at the plugs might help? If it will run on the choke but not without the choke it sounds like it needs more fuel to me (richen mix, check jets, fuel level, etc. to add more fuel)?

                              I haven't tried this with any of my more recent carby bikes, but my old dirt bike would stall on the choke when warm.


                              edit:
                              oh, also check for air leaks on any vacuum hoses or anywhere between the motor and the carb (split carby boot, carby not sealed properly in the boot, etc.). the carb may be fine, but if the motor is sucking air from somewhere it shouldn't the mix will be all fucked up even if the carby is in tune. Maybe worth a quick check before diving into the carb straight away...
                              Last edited by thro; 26-11-2014, 08:14 PM.
                              “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

                              Comment

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