Home Forums 2-Cycle Racing Kt 100 stalling.

This topic contains 12 replies, has 6 voices, and was last updated by  Walt Gifford 4 years, 1 month ago.

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  • #52569

    Tom Petalino
    Participant

    I’m having problems with my yamaha stalling on the warm up lap before a sprint race. When the idle drops below 5000 rpm it just shuts off. After digging into the carb today, I found the internal screen was dirty. Could this be the answer to my problem. I’m racing this weekend. Running senior pipe.

  • #52572

    TJ Koyen
    Moderator

    What are you carb settings?

    A Yamaha carb at race settings doesn’t really like to rev low, you need to keep the RPMs up a bit to keep it revving cleanly or it’ll load up. If it loads up enough, it’ll just bog and die.

    Driver/Coach/Wrench : Innovative Performance/Exprit
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    • #52573

      Tom Petalino
      Participant

      My low at 2 1/2 turns. High around 1/4 turn. I know these settings are for race conditions. On the stand I run my low around 1 1/2 turns. Problem is when we all bunch up to get ready to start guy in front brakes . I’m trying to keep revs up but, engine seems to just die. Once I get going it runs fine. I know it’s something I’m doing , I’m on brake and gas at same time to keep it running . Any time rpm drops it quits. Would running at 2 turns on low help?

  • #52582

    tony zambos
    Participant

    The carb settings sound good. Keep blipping the throttle on the formation lap to keep the engine cleaned out. At 5K, you should be way below the stall speed on the clutch. Wouldn’t close down the low end needle. As you know it gets busy on the first lap and you might forget to open the needle back up.

    LAD Specialties customer / tony kart / rotax / kt100

  • #52583

    Jim White
    Participant

    It sounds like it’s loaded up.  The clogged screen would hurt most at high rpms not just lugging around.

    Leaning the low would help but like said above you have to remember to open it back up. It’s all about tuning and knowing how to keep the engine cleaned out.

  • #52591

    FREDDY SANDOVAL
    Participant

    All the advice given above is correct, you may wanna check your clutch stall, if it’s too low it will stall ( goes into direct drive mode ) Should be around 8600.

    What king of clutch are you running? 2 disc, 3 disc, wet or dry?

    • #52596

      Tom Petalino
      Participant

      Currently running a horstmen 3 disc dry on my race kart. 9100 stall. On my practice kart I have a 2disc horstmen set around 8600 stall. Same carb on both. I don’t have any problems with the practice kart. Only the race kart. That’s why I posted this issue. I’m not familiar with carb specs. Still on the bottom end of the learning curve.

  • #52605

    Jim White
    Participant

    The “same” carb on both? Or the same “type” carb? No 2 walbros are the same in the way they tune. There are some better than others. When you find the “one” you will know it.
    You need to learn to tune on the fly. All the fast guys do it. Personally I would lean the low down for the start and then open it up as you get up to speed.
    An older fart than I used to say “tuning is tough” he was correct. It’s one of the more important things that separate the guys in front from the guys in back.

    • #52608

      Tom Petalino
      Participant

      Same type of carb. I’ll give it a try this weekend during practice. Start at 2 turns  then open it up as soon as possible. First two or three turns at pittrace are  fairly tight  and slow.  Thanks for the input. I have three different carbs to try. I assumed they would all be about the same.

      • #52702

        Tom Petalino
        Participant

        Update to this issue.  Having same problem in practice, switched carbs to a backup carb. Problem completely went away. I had no problem keeping the motor running.  Lap times were a little off but,  ran fine. Hope this helps someone at some point.

  • #52706

    tony zambos
    Participant

    Tom,
    First of all, thanks for the update. On the carb with the issue, you’ve had it apart and found dirt in the screen, but did you rebuild it? That would be a starting point. Pay attention to the tips of the low & hi speed needles for any deformations or if they’re broken off. Also check the inlet needle valve. Finish up by testing the pop-off. 9 psi is usually good.

    LAD Specialties customer / tony kart / rotax / kt100

  • #52712

    tony zambos
    Participant

    Tom,
    Double check the pulse line between the crankcase and carb for a tight fit.

    LAD Specialties customer / tony kart / rotax / kt100

  • #52721

    Walt Gifford
    Participant

    I’ve had most carbs that had to be set 1-1/2 or 2 turns. When I get on that needs 2-1/2 turns I think there’s something wrong with it.

    You’re revving it wrong on the line up. I can keep one going all day standing still. If you hold it open a certain amount it will feed a ton of fuel. Pop it open and closed every 2 seconds don’t try to idle it higher with the pedal.

    Gif

    FAA certified jet engine and aircraft technician,
    Nicholson Speedway class champion 2001,
    Yamaha KT100 Service Center,
    41 years karting experience

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