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  1. #1
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    Tmaxx classic tuning, shifting and smoke trail. Can't get a good balance.

    I'm having a little trouble getting my tmaxx tuned right. It idles good, good acceleration and smoke when taking off, run it out to top end, If I keep it rich enough to have a good smoke trail it won't shift. I can lean the hsn barely maybe 1/16 of a turn and it will shift every time, but the smoke trail is pretty thin. Temps today when running it was 70ish outside, and engine temps never got above 250.

    Sometimes when on the rich side where it won't shift, the rpms will climb like they should, no shift, and sometimes it'll get to the peak and sound like it fell off.

    I even tried turning out the transmission adjustment screw 1/8" of a turn, it hits 2nd a little better but still not every time.

    Running top fuel 20% about a quart and a half through it so far.

  2. #2
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    If you can't lean the top end any more do the pinch test on the bottom. If it's on the rich side then try leaning the low needle a little, no more than 1/8 to start. Could be that it's loading up enough on the low end that it's just not hitting enough RPM on high end. If you run it once and it doesn't shift and then do it again right after does it shift?

  3. #3
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    It is a touch rich on the lsn, pinch test is about 5-6 seconds, as far as the shifting goes it's sporadic, I can make 3-4 passes, it'll shift perfect, I can go for another pass, no shift, do another and right when it sounds like it'll shift it'll fall on its face, not cutting out just loses rpms.

    It may be tuned right when it shifts, but I'm watching smoke trails also, does traxxas fuel not smoke much? It's there, just not as pronounced as when I take off from a stop.

  4. #4
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    I don't know anything about Traxxas fuel. Long as you're seeing smoke on the top end you should be okay, but obviously the more smoke the safer. Sounds like you're a little rich on the bottom. Only way to cure that is to either lean the top a little, which also leans the bottom, or just lean the bottom a little. If you're happy with it on top try leaning the bottom a hair to see if it solves the problem.

  5. #5
    RC Qualifier nebulous.cow's Avatar
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    Id say what happens sometimes is the needles become out of sync. If your high is really lean and your low is really rich, or vice versa, they can affect each other for a little bit, and create the illusion that one is the wrong condition.

    When you do your high speed passes, really stretch them out. My touring nitros were especially hard to tune, the needles were not well 'separated' in the tuning process. So in order to get a proper reading on my HSN, I had to do a solid 5-8 second full throttle pass to clear out the crankcase, to get a good test result. I would often find my high to be too lean, and the richer low end was compensating for it. Same for tuning the low end, I would check its off-the-line acceleration right after doing a long full throttle pull. Like immediately after. To avoid the crankcase filling with excess fuel if my low was too rich.

    So really let your engine get into the ranges you are trying to tune. If you let it idle for a minute and then take off full throttle, odds are it has to chew through some excess fuel in the crankcase, and itll be rich that first pull. The HSN is designed for high speed. So really let it rip! But watch your temps, and its good that you are keen on the smoke trail. 250 isnt a bad temp either, but if you get to 270 or more, then start being more careful.

    Hope this helps.

    -Mike

  6. #6
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    Google Ron Paris "Tuning bible" and you'll find a post somewhere by a man that knew more about nitro RC engines than most people ever will. It explains a lot of what nebulous.cow is talking about. And it also explains why I tell people to set your idle gap properly FIRST when you get ready to tune, and then leave it alone until you have it tuned and are ready to make fine adjustments. Paris does a great job in his post explaining the balance between your HSN and LSN.

  7. #7
    RC Qualifier nebulous.cow's Avatar
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    This^^^^ Quality information there indeed!

    I did nitro helicopters as well, and tuning them was a handfull. 3 needles, and heli engines have the worst tendencies when it comes to needles affecting each other. It made me an infinitely better car engine tuner than I used to be. Especially since in helis, you don't control the throttle, a computer does, so you really have to watch and listen for what's happening. The more you know!

    Also, good mention on the idle gap, very important, I forgot to mention it. A bad idle gap usually also means a grossly out of tune LSN. If the gap is huge, your probably insanly rich on the bottom end if it idles, and if your gap is absolutely tiny, then you're probably really lean and your idle isn't smooth.

    Good info there.
    -Mike

  8. #8
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    Mr. Paris says leave that 3rd needle alone LOL! Unless you really know what you’re doing. I remember years ago someone (Thunder Chicken maybe?) made a MT with a ringed heli engine. A beast when it ran but really showed the difference between surface engines and those made for air. I don’t think the truck was around very long. Did you get your shift issue solved?

  9. #9
    RC Qualifier nebulous.cow's Avatar
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    Quote Originally Posted by cjtamu-redux View Post
    Mr. Paris says leave that 3rd needle alone LOL! Unless you really know what you’re doing. I remember years ago someone (Thunder Chicken maybe?) made a MT with a ringed heli engine. A beast when it ran but really showed the difference between surface engines and those made for air. I don’t think the truck was around very long. Did you get your shift issue solved?
    Yeah the heli engines are absolute power monsters, but only at a very specific RPM, and with a very specific pipe, and a very specific load. They basically run wide open the whole flight, but its the choice of the correct RPM and gearing that make it a torque monster. It took my 700 nitro 20+ seconds to spool up to speed, imagine that in a rc car! Lol. CVT rc car would be neat lol.

    Sorry to hijack, interesting stuff. Oh and as for the 3rd needle, I have begun experimentation with it on my OS21, and there really is a very small but important adjustment it makes, it really helps with taking off the line, after you've gained a few mph. My 21 tends to lean out right after the clutch locks and its accelerating in 1st, and richening the mid was exactly what it needed.

    -Mike

  10. #10
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    If you haven't already, Steve Bess wrote an article years back about not being afraid of your mid-range needle. Good read if you haven't seen it already. He can tune.

  11. #11
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    I ran 2 tanks of Morgan sidewinder 20% 12%oil, Man, it woke the tmaxx up. Faster, sounded better, banged second gear every time, and still had better smoke trail than the top fuel, granted not as thick as I wanted, but better. And the top of the piston is now a nice honey color, with the traxxas stuff it was a nasty gummy brown color. And it still has enough oil because the side of the truck was covered and the tip of the exhaust had some build up on it. Apparently my maxx doesn't like the traxxas fuel for some reason.

  12. #12
    RC Qualifier nebulous.cow's Avatar
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    Quote Originally Posted by jjshultz78 View Post
    Apparently my maxx doesn't like the traxxas fuel for some reason.
    You're not alone in that finding. I've tried a variety of brands of fuel and different mixtures and such, and unfortunately, Byrons has always been the winner in my book, but theyre gone now. Im using the last of the liquid gold I have, and if I ever see it on a shelf again, I'll swipe that right away. I've had good luck with VP, sometimes it's a little thin on the oil package for hot days though.

    Make sure you're not 'compensating' for tuning issues by switching fuels. Changing to any other brand of fuel will require some amount of re-tuning, so just be aware. I've never tried the sidewinder fuel specifically, but my local nitro shop stocks it, so someone must be using it! Different oil packages just work better in certain conditions too, and maybe you switched to a more ideal mixture for your driving and air quality. Glad its running better!

    -Mike

  13. #13
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    Glad you got it solved. Sidewinder is good fuel. I don't think you'll be disappointed if you try it. As an aside, after running one truck on 20% and one on 30% I've decided I like the 3.3 better on the 20%. More stable and I like the power band better. Just IMHO, but I'm sticking with 20%.

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