Home Forums Tech Talk Kt100 WB3A on track tuning help

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    • #35685
      Lawrence Doty

      I’m new to the KT100’s
      No history on the carb/motor (craigslist purchase)
      Currently using an open (A2) pipe. But will be getting an RLV3 pipe for next year.
      I rebuilt the carb. Reused the fulcrum and spring.
      Pop off is at 11
      Not sure what the fulcrum height is…don’t have a gage yet…
      I’ve been on the sprint track 2 days now. Day 1 I had the wrong gear and the motor was turning 16k at the end of the straight…changed gears, got it down to just over 14k.
      After doing a TON of reading and searching…I understand about the motor not idling on the grid and bogging under a load coming off the grid. I can turn the low needle in, get it to start and get off the grid, then open it back up once I get on the track.

      Now for the fun part…what am I listening for, looking for or want to feel in regards to tuning on the track?
      No EGT but I do have a head temp sensor. Highest I saw so far was 399.

      When turning the High and the low needles what should I expect to see/feel?
      What do I want to see/feel…other than better lap times…

    • #35693
      patrick hubbell

      Lawrence, lots of good questions.  pop-off should be more like 9 to 10. I would look for an experienced kart shop and have the inspect the carb to be sure it’s legal. 16K, never seen a KT turn that many revs.  At least not for long.  CHT is almost useless by it self. To many variables. Get EGT if you can. I have to go, will continue later.

    • #35720
      Lawrence Doty

      Downloaded the data from the MyChron to the laptop and realized that the 16k rpm wasn’t accurate…graph had some wild highs and lows. The 14k runs look a lot smoother so those I trust.

      Also rechecked the pop off. The carb popping off at 11 leaks really bad. I get one good pop and then it never re-seats itself and leaks out all the pressure. Tried several needles old and new…no change…other then blowing it out with air, is there anything I can do…or is this body done…?

      FYI..I’m filling the seat with WD40.

      The other carb I have pops off at 8 and drops down to 4 no leaking…guess which one goes back on the motor???

    • #35859
      Lawrence Doty

      Posted by Brian in another thread;

      You may want to put some teflon tape on the needles for you carb, that will help seal it up.  Those carbs always pumped too much at the top, and not enough at the bottom, the high speed can be closed down quite a bit, and the bottom opened quite a bit. if your bogging off a turn, your lean, open it up.  If you 4 cycle down the chute, lean out the high speed.  Check the plug or head to see if your too rich or lean.  You want a nice coffee color tending to grey.  Grey is too lean, black too rich.

      And clarify that it’s the Inlet needle (seat) that’s leaking.


      • #35941
        patrick hubbell

        You shouldn’t need Teflon tape to seal any part of the carburetor.  It is normal for the needle to pop once and then leak down.  You have a Mychron and are able to download data, excellent. All you need is EGT and you are set.

        Why EGT over CHT.  EGT responds instantly to changes in temperature. CHT responds much slower to changes in outside temperature, casting type, pipe etc. When tuning with EGT, you always want the temp to be increasing to some unknown maximum and it should increase quickly as soon as you open the throttle. Start with the “L” speed needle set at 1-1/2 turns and the “H” needle at 1/4 turn.

        Note: the low speed circuit feeds gas to the engine up to 12,000 rpm then the high speed circuit opens and both high and low are feeding the engine.

        Once the engine is up to temperature, open the “L” needle to 1-3/4. As you get close to the end of the longest straight, the engine may be to rich and loose power. This is called “four cycling” and sounds like “blaaaaaa” open up the H needle an 1/8 turn more, if the engine is still 4 cycling then lean the “H” needle 1/8 turns at a time until the engine runs crisp all the way down the straight. If the engine is lazy off the corners , richen the “L” an 1/8 turn.  If the engine is stil lazy then you might have to adjust the pipe’s length, the gear ratio or the stall speed of the clutch.

    • #35962
      Lawrence Doty

      Thanks, that’s the kind of info I was hoping for.

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