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Anybody good with 4-Stroke Dirt Bikes? YZ400f

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  • Anybody good with 4-Stroke Dirt Bikes? YZ400f

    We have a 99 YZ400f that we bought a couple years back. It ran like a bat out of hell and then we let it sit for a while. Mom let a guy take it to a shop to do the maintenance/cleaning on it and all they did was completely disassemble the carb. I just spent 5hrs thoroughly cleaning everything and reassembling it, although I didn't do any tuning. It used to start on the first or second kick and now I can't keep it on. I'm done dicking with it and we are getting ready to sell so I wanted to know if anybody was awesome with these and wanted to tune it for me while I provide you with an abundance of beer or burgers or some cash. Definitely don't want to pay dealership prices so let me know if you can help!

  • #2
    Location is Mesquite/Sunnyvale area near Belt Line and 80.

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    • #3
      motorcycle sub-forum would be a better place to ask.

      pretty sure kingjason is familiar with the 400-426f

      what's it doing exactly?

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      • #4
        Set the mixture screw 1.5 turns out from lightly seated. Did you pull the pilot, main, and enrichener jets out and physically clean and look through them. The pilot jet will affect its idle and overall running. I'm fluent in the 400 and 426, I have a 99 and just finished a motor build on my buddies 01 this mornig @ 2 am. I'd look at it but there's a huge distance gap.

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        • #5
          Also, while the pilot is out i usually pull the mixture screw and run carb cleaner througj the mixture and pilot passages, they are inter connected.

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          • #6
            I'm not sure that the orifices of each of those jets got clean enough.. I have the pilot at 1 1/4 turns out as per the manual but I can't keep it running. I got the carb assembled, turned the fuel on, bowl is filled, choke on, I can get it to crank up for a few seconds with the idle up a little but it doesn't stay on. I kicked for about 15 minutes before getting exhausted and tearing my shoe up. Lol

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            • #7
              It.has an accelerator pump, hit it a fw times before kicking to prime it. Sounds like the pilot jet is clogged. I use a torch tip cleaner or a wire bristle pulled from a wire brush to clear it out.

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              • #8
                I can pull the pilot jet and clean it all out. What does the accelerator pump look like and how to I hit it? I thought it was just the spring loaded diaphragm mounted on the carb.

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                • #9
                  Originally posted by shumpertdavid View Post
                  It.has an accelerator pump, hit it a fw times before kicking to prime it. Sounds like the pilot jet is clogged. I use a torch tip cleaner or a wire bristle pulled from a wire brush to clear it out.
                  this. pilot controls idle to quarter throttle. also, make sure your float is at the correct height

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                  • #10
                    I don't think the float height was changed since it was running, but I did notice that those phucks dinged up the float needle entrance, although it doesn't affect the float or needle movement.. I'm wondering if that could cause a problem though. I think the point of the float needle is still seating fine so it shouldn't affect it. The float height is only adjusted when the carb is apart and floats visible right? I'll pull the pilot tomorrow and clean it thoroughly and the seat as well to see if that helps

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                    • #11
                      With the air box off you should be able to twist the throttle and the little brass nozzle sticking up into the bore of the carb, behind the slide, coming from the bottom should spray fuel. It will be a small stream shooting into the motor.

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                      • #12
                        On the dirtbike carbs, I like to totally disassemble them and pull every jet, needle, etc... then I put them in my wife's sonic jewelry cleaner and run it twice on the longest setting. Night and day difference and gets rid of all the crap in the orifices that you simply can't get to. Plus my wife LOVES it when I use it to clean car/motorcycle parts.
                        Originally posted by stevo
                        Not a good idea to go Tim 'The Toolman' Taylor on the power phallus.

                        Stevo

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                        • #13
                          Hmmm. My dad is a Jeweler so if worse comes to worse, I may end up doing that. lol

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                          • #14
                            check valve lash...........
                            pinto gt with wood trim

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                            • #15
                              Do you have a sales price in mind?

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