Home Forums TaG Rotax Max FR 125 stalls when taking off

This topic contains 8 replies, has 2 voices, and was last updated by  EJ Korecky 2 months ago.

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  • #96537

    EJ Korecky
    Participant

    Runs strong all thru the power band after take off, but stalls when leaving the line if you don’t feather the throttle – if you give it full throttle, it stalls almost immediately. Float heights were set at 5mm, dropped it to 3 – planning on testing next week to see if this cures the issue. Any other ideas or suggestions would be appreciated.

    PV 8 clicks, 162 main, 2 1/2 turns air screw. Max EGT 1250, Max RPM 12800, Max water 146, Plug BR9EIX – looks spot on, battery fresh/full charge always, Reeds intact. Could this be a sign of a weak coil?

    Thanks,

    ej

    • This topic was modified 2 months, 2 weeks ago by  EJ Korecky.
  • #96539

    William Martin
    Participant

    Might try turning in the air screw a bit. Does it gag on the stand if you give it full throttle from idle? If so, turn the air screw in about a 1/4 turn and try again, repeat until you get decent throttle response. Hope this is useful!

    Bill

  • #96541

    EJ Korecky
    Participant

    On the stand, holding the brake and flooring it causes it to stall. I am assuming that it is rich on the bottom – wouldn’t closing the air jet richen it more? I will give it a try though.

    inner pilot B45, outer pilot 50, needle K22,

     

    Thanks for the reply,

     

    ej

  • #96565

    William Martin
    Participant

    Not familiar with what “typical” jetting is for that engine/carb combo, but if the plug looks good I wouldn’t change float height or main jet. It may be that your pilot jet is too big, and the air bypass has to be adjusted way out to make it idle. The fix for that is a smaller pilot jet and turn in the air screw a bit. I’m just going on a prior experience with a Honda shifter that developed a terrible bog when going full throttle. What had happened was the air screw had vibrated loose to where it was about to fall out… as soon as I put a new O-ring on the jet and set it back to where it was happy before, all was well with throttle response. You can easily try turning in the air screw, don’t worry about good idle, just keep it turning fast enough to not stall while you do your search for correct air screw setting. The important thing here is to stay on the safe side with jetting changes…go slowly!

    Bill

    ps: just fyi, if it runs good at full throttle, it isn’t weak ignition parts.

  • #96566

    EJ Korecky
    Participant

    Did some testing today…started with air screw at 1/2 turn, and went  in half turn increments to 3 turns with no change whatsoever. Tried the needle in clip in every position – no change. Tried leaner pilots – no change. Tried a new battery – no change. Without feathering the throttle at take-off, it stalled every time.

    Here is what I noticed – when I removed the atomizer tube (DQ 266), I noticed that it does not really seat on the atomizer bush, or carb body. The outer hex part of the tube just tightens onto the internal threads on the carb body. Without it seating, I am assuming that fuel can just get sucked past the threads into the Venturi – so it makes sense that no matter what I do, it will always be rich on the very bottom. Kinda explains why my mains have always been much leaner than others racing in the same class. I dripped some fuel onto the base of the atomizer when installed and actually watched as fuel dripped thru the threads into the Venturi part of the carb.

    Maybe its time to upgrade to the new EVO carb…

    Thanks for the ideas and suggestions,

     

    ej

  • #96580

    William Martin
    Participant

    Wow, that’s a strange one. Just out of curiosity, has it always behaved this way, or is it a recent change? It would be really good if you could borrow another carb & swap the whole thing out to see if the problem goes away. Just hate to go buying a new carb without that one sanity check!

     

  • #96584

    EJ Korecky
    Participant

    Not a new issue – has always struggled off of the line. I took 2 pics, but not sure how to post them here.

     

    ej

  • #96592

    EJ Korecky
    Participant

    Bought a new evo carb, and there is a major difference. Solved the problem instantly. Video link attached comparing the two. Either the original carb was not machined correctly, or it was a flawed design from the beginning.

    https://youtu.be/AqMkE8L5K-s

  • #96892

    EJ Korecky
    Participant

    Just wanted to post a follow up of an additional change I made…

    Engagement RPM has always been very low – around 2600 with new stock shoes and springs. This, coupled with the carb issue really made this engine struggle off of the bottom. I machined the shoes and got the weights down to 53 grams each (stock shoe weight is 64 grams). Engagement is now at 3700, and it is a completely different engine off of the bottom. Was considering the new EVO clutch, but with this change I no longer see the need.

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