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    Bros 400 re-jetting

    Hi all, I'm new so please excuse the incredibly simple question, but.. is rejetting the carb because of after market filter, exhaust, etc. Just a matter of buying a bunch of sizes of jets, warming the engine up, and then trying out different jet sizes and screw settings on the carb until the idle is good?
    cheers!

    #2
    A little more intricate than that I'm afraid. Depending on the exhaust and intake, you'll need to do a few test rides to make sure there are no gaps in the acceleration and idle good. It may be overkill, but on a new bike I always start at baseline.... Meaning I do a valve adjustment check and get it running perfect with stock setup first, then I go into the modifications. Many may agree or disagree with this step, but I've always found it beneficial to start with a good baseline.

    Once the timing, valves, idle, and stock acceleration are as best they can be, that will hopefully assure a smooth transition to the modified setup. (not to mention some piece of mind)
    Otherwise, buying a bunch of jets and trying out the different sizes is pretty much the technique. You gotta learn the process somehow. Once you've done it enough times then you'll see where the flat spots are and hopefully, fiddle with your mixture screws, shim your needles, adjust floats accordingly.

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      #3
      you need to study to the TUNING INSTRUCTIONS furnished with k&L /dynojet and factory pro kits, available online i believe.

      "select the best (highest speed) main jet FIRST."

      guys on here can give good jetting info if you state what exhaust and air filter you're using, altitude and etc.
      squirrelman
      Elite Hawker and Carburetor Master
      Last edited by squirrelman; 07-29-2021, 01:00 AM.
      "It's only getting worse."


      MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

      Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

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        #4
        Another thing to do is make sure the carbs are balanced, and for me the next thing to do is check the plugs to see if the motor is running weak or rich. Also if the bike is running ok now, before you do anything make sure you have a good reason to make an adjustment, and do not rush into making adjustments.

        Comment


          #5
          Originally Posted by Toxicwst View Post
          A little more intricate than that I'm afraid. Depending on the exhaust and intake, you'll need to do a few test rides to make sure there are no gaps in the acceleration and idle good. It may be overkill, but on a new bike I always start at baseline.... Meaning I do a valve adjustment check and get it running perfect with stock setup first, then I go into the modifications. Many may agree or disagree with this step, but I've always found it beneficial to start with a good baseline.

          Once the timing, valves, idle, and stock acceleration are as best they can be, that will hopefully assure a smooth transition to the modified setup. (not to mention some piece of mind)
          Otherwise, buying a bunch of jets and trying out the different sizes is pretty much the technique. You gotta learn the process somehow. Once you've done it enough times then you'll see where the flat spots are and hopefully, fiddle with your mixture screws, shim your needles, adjust floats accordingly.
          mixture screws have little effect after about 3000 rpm and won't tune out flat spots above that, and floats MUST be set to factory specs.
          "It's only getting worse."


          MY rides: '97 VFR750, '90 Red Hawk, '88 Blue/Black Hawk, '86 RWB VFR700 (3), '86 Yamaha Radian, '90 VTR250, '89 VTR250 (2), '73 CB125, '66 Yamaha YL-1

          Sold: '86 FJ1200, '92 ZX-7, '90 Radian, '73 CB750, '89 all-white Hawk, '88 blue Hawk, '86 FZ600, '86 Yam Fazer 700 , '89 VTR250, '87 VFR700F2, '86 VFR700F.

          Comment


            #6
            Thanks for the replies lads, really helpful. Just had some pods laying around so I slapped them on to see what it was like. Seems the start easier now but have a bit of popping on decel. So I'm probably running lean ?

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              #7
              Also seems to be quite a contentious topic but with stock exhaust pods won't do much I've read ?

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