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  1. #1
    RC Enthusiast gandalfnz's Avatar
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    Problem with TRX 2.5 at half thottle

    Hi Guys

    I am not sure why Nitro Rustler section is not work, when I post a thread in there, it just vanishes.

    Anyway, I have a Nitro Rustler which I cant figure out what is wrong with.

    The engine is complete gutless after a WOT pass.
    If I was to do another WOT, it would go like its half throttle, even though I have the trigger fully pulled.

    Or, if I run it about half throttle and then want to do a WOT, gutless again.

    If I then let it sit idle for a few seconds and take off again, it runs normal as it should.

    Its almost like I need the engine to load up on fuel a little so that I can reach full speed.

    Not sure if this means that the engine is near the end of its life.

    Thanks a lot for your support.

  2. #2
    Marshal Double G's Avatar
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    With the engine off do a test (simulate the length of time of your WOT pass) with the electronics and see what happens to the servo - does it open halfway or full the second time around? What batteries or pack are you using? If it passes that test, then make sure the system is air tight from the air filter to the pipe.

    What sound is it making? Does it sound like it is choking (think Chewbacca) which is lean or just does it seem like it takes a while to get up to speed and has a bit of smoke (rich)?
    The Super Derecho

  3. #3
    RC Enthusiast gandalfnz's Avatar
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    Quote Originally Posted by Double G View Post
    With the engine off do a test (simulate the length of time of your WOT pass) with the electronics and see what happens to the servo - does it open halfway or full the second time around? What batteries or pack are you using? If it passes that test, then make sure the system is air tight from the air filter to the pipe.

    What sound is it making? Does it sound like it is choking (think Chewbacca) which is lean or just does it seem like it takes a while to get up to speed and has a bit of smoke (rich)?
    Its hard for me to explain.
    Its definitely not the lean bogging sound.

    It sort of gargles likes its running super rich, then takes off really nice. But it doesn't always do this, and its also not that typical running rich drowning sound.
    If I accelerate nice and slowly it will always reach top speed.
    If I do a WOT and then keep revving it until I turn around and do another pass, it always will not take off and reach top speed, until I stop and wait a few seconds then take off again.
    It needs to load up on fuel for it work as it should.
    If I don't stop and keeping reeving it even more it will either run completely gutless or just shut off.

    The engine has seen a fair bit of use, so not sure if maybe needles and carb need cleaning, or engine is just nearing its end.

    I have another nitro rustler which hasn't had a lot of fuel trough it and managed to tune it really well. Runs great.

    Thanks
    Last edited by gandalfnz; 01-20-2020 at 01:10 PM.

  4. #4
    RC Champion
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    Try replacing your fuel line and also the fuel filter. Try and make sure there are no sharp bends or kinks in your fuel line as well.

  5. #5
    RC Champion grizzly03's Avatar
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    What are your needles set at? Idle gap? Have you tried going back to factory settings and retune? Sounds like your needles could be set wrong. What happens to engine RPM after a WOT pass? RPM's hang high for few seconds or drop?

    My quick guess (One is set rich and the other set lean). HSN set lean, LSN set rich, idle opening more than 1mm.

    My experience with a bad engine is no matter how I tune it, it had no power and/or overheats.

  6. #6
    RC Enthusiast gandalfnz's Avatar
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    Hi

    Let me try and answer the all the questions asked.

    I did a WOT simulation without driving the car and the servo opens normally, it never jams or goes hard.
    I am using Eneloop NiMh batteries for Tx and Rx.

    I have removed the fuel lines and tested them for leaks, have blocked one end with a finger and blew air on the other. They seem pretty air tight to me.
    The same air filter I used on my other Rustler which runs flawlessly.

    LSN is one or one and a half turn out from flush.
    HSN is almost 5 turns out.

    Now keep in mind please, that at almost 5 turns out I get temps are around 230F. Its very hot and dry outside with temps around 85F.
    For LSN, if I lean it even a tiny bit more, my idle goes too high, so much that the car starts to spin the wheels and wants to take off.

    Idle gap is around 0.5 mm, almost at a minimum.

    Thanks for all your help!

  7. #7
    RC Champion grizzly03's Avatar
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    When you lean the LSN your idle would go up, then you would lower the idle with the idle screw to lower it back down. Don't think that because you have your gap set you cannot close it more. The factory settings are a starting point only. What does the LSN pinch test show you.

  8. #8
    RC Enthusiast gandalfnz's Avatar
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    Hi Guys

    Sorry for not replying for a while, I haven't had the time to play with the Rustler in a while.

    I am still having issues with one of the Rustlers (sold the well used one).
    The one I have left is almost new, engine looks and feels new, compression is really good.
    It has been sitting idle for a very long time before I purchased it.

    Engine still has a very high idle. I can tune the HSN fine, but LSN is giving me headaches.
    LSN is tuned to 3-4 seconds pinch test, temps is also around 250F, but it just idles too high.
    The only way to lower the idle is to richen the LSN more, but then the car is too rich to even take off when starting from cold. If I pre heat the engine, that hides the super rich LSN somewhat.

    The most interesting thing is that lowering the idle screw does nothing, absolutely does not lower the idle at all. I checked and carb slide is moving when unscrewing the idle screw, linkage is also good.

    I am almost certain it that since idle screw does not lower the RPM, engine is drawing air from somewhere else, but from where?
    I did a leak test on the front bearing and yes its leaking, but not much as the fuel does not leak or get flung around while running. From what I have read, its also normal for these to leak a little.

    Any ideas? Maybe some of the seals are bad from not being used so long. Carb LSN seal, or backplate seal.

    Other than that, the Rustler runs great and its my favorite Nitro RC, its so simple to work on and parts are readily available. We have a Slayer Pro and Revo 3.3, but somehow I just always end up using the trusty Rusty.

    Thanks
    Last edited by gandalfnz; 04-13-2020 at 05:27 PM.

  9. #9
    RC Champion grizzly03's Avatar
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    Check your exhaust for leaks (coupler) and check that the fuel tank cap is sealing. Also if you have taken the carb off, check the O-rings that seal the carb to engine block are still good.

  10. #10
    RC Enthusiast gandalfnz's Avatar
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    It will have to wait yet again, but I was thinking next time I might get WD40 and spray it at all the usual leak spots, see if the engine changes a tune or stalls when it sucks in WD40?

    Just an idea?

    Its all put together now again, not sure when I will have the time to take it apart again, but I will report back eventually.

    I have a bit of doubt that my tune might be to blame, but I have tried so many times and always end up in the same position. Idle high, LSN rich. Idle game is less than 1mm (0.8).
    Decreasing idle gap does not lower the idle.

    Fuel cap I already checked and it seems to be tight, blew trough a tube while lightly holding my finger over the cap and no air was getting out.
    Last edited by gandalfnz; 04-13-2020 at 09:55 PM.

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