Home Forums Shifter Karts CR125 Too Lean?

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    • #53592
      Todd Kageals
      Participant

      Guys,

      I have been driving long enough that I am starting to play around with the tuning on my kart (stock Honda CR125, Keihin PWK, pump around).  I have been running a 180 jet for the past 3 years!  The kart has always run well and has been very durable.  We do about 8 race weekends a year which for us works out to about 10-12 days (some sprint, some road race).  This weekend I dropped down to a 175 jet which according to some should have still been on the rich side.  We run 110 Sunoco race fuel mixed at 20:1.  On the long front stretch, at WOT, I would start to hear and occasional “pop” from the exhaust.  I would also hear the “pop” anytime I was at full throttle for more than a few seconds (always as the revs started to get to around 11K or so.  This caused me to short shift but there was not much I could do on the straights.  I can’t really read the plug (it always looks the same to me!).  I pulled the head to check the piston.  The piston surface (new before this race) is a light tan and feels like sand paper.  The is one tiny ding on the surface of the head and some very tiny marks around the flat portion of the head.  Otherwise the head is very shiny and clean.  Does this all sound like the 175 was too lean?

    • #53594
      jim lewis
      Participant

      Todd,

      The pop and lack of power indicate a lean condition. Light tan on piston also indicating a lean condition.

    • #53627
      Chris Hegar
      Participant

      1999 kit motor or 2001?

      What pilot and needle?

      I’m guessing this was at Buttonwillow?

    • #53733
      James O’Brien
      Participant

      Your piston should be smooth and covered in carbon.

      www.eshifterkart.com

    • #53740
      Rodney Ebersole
      Participant

      James O’Brien, Going from 20 parts gas and 1 part oil, to 32 parts gas and 1 part oil is not adding more oil to the mixture.

      • #53786
        James O’Brien
        Participant

        Ratios and drinks do not mix, thanks for the correction Rodney

        www.eshifterkart.com

    • #53776
      Jimmy McNeil
      Participant

      20 to 1 is a rich mixture (even for road racing) and may even be contributing to the speckling your seeing on top of the piston. Think that comes out to 6oz per gallon, go to 4.5 or 5 oz. Running a rich fuel/oil mixture = leaner in the combustion chamber. The popping your hearing is common with a lean condition.

    • #54814
      Todd Kageals
      Participant

      1999 kit motor or 2001? What pilot and needle? I’m guessing this was at Buttonwillow?

      Chris,

      This was actually at Summit Point, WV.  I don’t know what pilot I was running as I have never swapped the pilot.  I was under the impression that the pilot only affected the mixture at part throttle (I’m almost never part throttle at SPR).  The popping only occurred at full throttle on the main straight.  Needle was DGJ.  I think 20:1 is the spec ratio for our club.  The motor is a ’99 but I built it from an old dirt bike motor (completely rebuilt including the 6 speed).  I did notice that I am missing the rubber boot that goes on top of the carburetor around the cable.  Not sure how much that would affect it.

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