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  1. #1
    RC Competitor
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    When I engage the break idle falls

    Went out to the RC dirt track today and because I'm the , I most ran in the Midrange on the throttle and I could tell it was a bit rich. I leaned out the LSN then needed to lower the idle.

    Ling story short, when I engage the brake I can see movement on the carb slide and I'm betting close to a millimeter, and slowing the idle down more.

    How do I set the car so the carb is fully closed when there is no throttle being applied? I have not messed with TQI settings for the different trims.

    Thank you
    Last edited by Double G; 01-19-2020 at 06:43 PM. Reason: Language

  2. #2
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    I think I found it. Looks like the stop may have moved.


  3. #3
    Marshal Double G's Avatar
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    The carb should not fully close at idle unless you want to restart the engine every time you stop. 0.7-1.0 mm open at idle.


    And watch the acronyms as well. Per Traxxas: no no.
    The Super Derecho

  4. #4
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    Quote Originally Posted by Double G View Post
    The carb should not fully close at idle unless you want to restart the engine every time you stop. 0.7-1.0 mm open at idle.


    And watch the acronyms as well. Per Traxxas: no no.
    It wasn't, the problem was in the servo box for the throttle / brake box. Clue me in as I'm not sure of the terminology but the rod to the carb, has a stop, (round with set screw) apparently it moved and it was holding the carb open, and braking, made the carb close to the idle set screw.

    It may have been there from the factory, as I never noticed it until I tried to lean out the midrange.

    Also I don't remember the acronym If you remember shoot me a private. Thank you

    Last edited by CBerry; 01-19-2020 at 11:07 PM.

  5. #5
    RC Champion olds97_lss's Avatar
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    The idle set screw on the carb should be set so that it can't fully close regardless of the servo linkage. When the servo is at "idle" postion, the carb slide should be resting on the idle screw in the carb itself. When you apply brake, the set screw keeps the arm from moving further at all mechanically.
    Expert rigging at it's best!

  6. #6
    Marshal Double G's Avatar
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    In addition, the collar on the linkage should have a very small gap between it and the horn at idle. You may not have it adjusted correctly and when you apply the brake the two separate and the carb can close until it hits the idle screw.
    The Super Derecho

  7. #7
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    From experience if you donít have the linkage setup correctly it can close the carb enough to make it stop at idle. Make sure you have checked the linkage and made sure it is set correctly as it can make the truck die at idle.

  8. #8
    Marshal Double G's Avatar
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    The carb will close only as far as the idle screw will allow - no further. The linkage and collar are not to be set up to set the idle.
    The Super Derecho

  9. #9
    RC Competitor
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    It's fixed guys. It was all in the linkage. I have no gap now doctor G I'll add it in.

  10. #10
    RC Champion
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    Yup the linkage if not set correctly as I said, can cause issues. Glad you got it sorted!!

  11. #11
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    Quote Originally Posted by 222 View Post
    From experience if you don’t have the linkage setup correctly it can close the carb enough to make it stop at idle. Make sure you have checked the linkage and made sure it is set correctly as it can make the truck die at idle.
    If this was true why do all carburetors have an idle screw? The screw keeps the throttle from closing too far.


    Quote Originally Posted by Double G View Post
    In addition, the collar on the linkage should have a very small gap between it and the horn at idle. You may not have it adjusted correctly and when you apply the brake the two separate and the carb can close until it hits the idle screw.
    Quote Originally Posted by Double G View Post
    The carb will close only as far as the idle screw will allow - no further. The linkage and collar are not to be set up to set the idle.
    This is the correct way.

  12. #12
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    Grizz. On mine the collar either slid down the rod against the servo arm or it came that way. It does not make sense to me how this kept it open. When I hit the brake I could see the carb slide close, to the limits set by the idle screw. I really never experienced this issue before I tried to lean out the LSN which caused the idle to increase. I attempted to adjust the idle and that when I noticed the problem. The only thing I did to solve the throttle movement when I braked is adjust that collar. Only thing I can figure is the idle screw was screwed way in, and the tune made it run decent. I was running a lot in the mid range and the engine had that popping sound when the engine is rich. I keep turning the idle screw counter clock wise trying to turn the idle down and when I got it about right then the idle would drop and stall when I applied the brake. That is the only explanation I have.

  13. #13
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    CBerry, My post wasn't aimed at you. 222 said that the throttle can close too much to let the engine die at idle. I was just repeating that the idle screw controls the idle not the throttle linkage. If someone sets the idle with the linkage and not the idle screw, every time they hit the brakes the throttle barrel would close more than having the idle screw stopping it from closing more.

    After setting the idle screw you would need to check the gap on the collar because if you lower the idle screw the gap between the servo arm and collar gets smaller. If there was very little gap to begin with, this is why you noticed an issue after adjusting the idle. That's the biggest reason for the gap, to allow for small idle adjustments.

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