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Both smokers down with the same ailment

  1. #1
    Lifer Kurlon's Avatar
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    Both smokers down with the same ailment


    This started with my KTM. Took it for a short road ride last week and discovered along the way that if I hammered the throttle it'd cut out on top as if I hit the kill switch. Well, the bike hadn't moved since some time last summer, same gas... gotta be bad fuel, right? So into the corner it went, tank drained.

    This weekend I went to Canaan for the first time, and brought my motard. My first session out I heard it starting to detonate on top in 4th and 5th once warm, so into the pits, mixture richened, and when that didn't clean it up I tracked down a can of Sunoco 260GT to throw octane at the issue. Prior to this it had only been run at short tracks since rebuild, and never been wrung like this.

    Well, that helped, no detonation and I was able to start trying to learn the track. Once I started to build a line I was finding out that my gearing was a lil short as I held it WFO for longer and longer. Guess what started to happen? Same symptom set, if wrung out in 5th it'd cut out. Close the throttle for a moment and it'd respond again. Ok, WTF, retired the machine for the day.

    Come home, put clean, fresh gas in the KTM and it's doing it even sooner than before, 1/2 throttle is enough to piss it off so bad it'll actually stall out, requiring kicking to refire. Whatever is going on with one I suspect is going on with the other. I could believe a crank seal leak on the KTM due to inactivity. The motard absolutely has not sat this year. I also don't get why it literally shuts down until it's coasted for a moment with closed throttle, I would expect an air leak to recover quicker when the throttle closed? I would like to implicate the gas, but the motard is running from a fresh, previously unopened can of 206GT. I'm going to try and rig/beg/borrow/steal a setup to leak test both motors. In the mean time I've pulled the plug on the motard, it's reading a touch rich which I would expect given I purposely fattened it up, borescope says I didn't damage the piston or cylinder, and the only crank movement I can find is a touch in and out, no side to side / up and down. Brake and parts cleaner on the ignition side seal while the bike is idling doesn't do anything. Oil drained out, no signs of being down, no fuel smell, bike is not smoking excessively.

    Does this symptom set ring a bell with anyone else?

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  2. #2
    Lifer Chippertheripper's Avatar
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    Re: Both smokers down with the same ailment

    It doesn't, sadly.
    All I can tell you about the KTM is you should follow the manual's directions, and nothing else. KTM's are not finicky in any way when jetted as the manual states.
    That , at the very least, will eliminate your jetting as a possible cause.

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  3. #3
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    I haven't actually touched the jetting on the KTM, never had reason to. Prior to this it's run like a top, putting in the woods at mind numbingly slow speeds or short rips on the road like an idiot. All the teardown / inspection / fuckery has been with the motard so far.

    One other note, the theory I left the track with was poor fuel flow into the carb (motard) resulting in leaning out on top. (And thus detonation or cut out.) Given both are doing it, I'm now mostly confident that's not the issue.

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  4. #4

    Re: Both smokers down with the same ailment

    Video?

    And full disclosure, you have read my posts...I usually ask you for the all-knowing advice LOL

    Yeah...uh...check the valves

    Fresh plug?

    If it was fine til you rung out on top then fine after closing then it's not happy when top temp hot or running out of fuel delivery?

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    Last edited by breakdirt916; 08-27-17 at 03:17 PM.
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  5. #5
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    No vid, but the best description I can give:

    Cruising along at in 5th at 50mph on the street, maint throttle, all is good. Roll it on slowly and we're pulling more and more, good. WFO and the bike responds, here we go and, wait, was that a misfire, and now nothing, no fire at all, just coasting. If you close the throttle the engine braking increases slightly, and then after a moment you notice the slight surge of being slightly lean at closed throttle, it's firing again and it'll accept throttle again.

    If when it cuts you stay in the throttle, or you don't wait for it to refire before twisting again, it just refuses to do anything. If you're going too slow (KTM, 'cause it's doing it sooner now) you will stall to a stop when it acts up.

    The warning, if you get one feels like lean jetting causing it to miss/detonate. Once it dies it feels like electrical, no spark at all.

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  6. #6
    Soul Rider Paul_E_D's Avatar
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    Re: Both smokers down with the same ailment

    Quote Originally Posted by breakdirt916 View Post
    Video?

    And full disclosure, you have read my posts...I usually ask you for the all-knowing advice LOL

    Yeah...uh...check the valves

    Fresh plug?

    If it was fine til you rung out on top then fine after closing then it's not happy when top temp hot or running out of fuel delivery?
    No idea why two bikes would do the same thing, but: replace plug, plug cap, fuel, xlean amd inpect jets, reeds, airbox, filter and try again.

    Remove head and inspect for actual det marks. Check coolant.

    There's not much else

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  7. #7
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    Plug in the KTM is one heat range colder than the book calls for, reading way fat. I should inspect the jetting at some point. Replaced with a new Irridium fine point of the right heat range and on a short test ride was able to hit ludicrous speed. (Floating the front at 75mph on knobbies on pavement is always exciting.)

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  8. #8
    Posting Freak jimmycapp's Avatar
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    Re: Both smokers down with the same ailment

    Do you know what lean and rich feel like in a 2 stroke? I do, but I've never felt detonation. Not sure what that's like on a two stroke. Check to make sure a jet didn't loosen up and make is rich (4 stroking). I had a cracked carb boot, from sitting, that caused a lean 1/4 throttle.

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  9. #9

    Re: Both smokers down with the same ailment

    What the hell 75mph floating the front

    I did a freeway wheelie at 65-70ish on a night stunter/sportbike group ride and ran out of rpms when it came down

    2 smoke madness

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  10. #10
    Soul Rider Paul_E_D's Avatar
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    Re: Both smokers down with the same ailment

    Detonation feels like a tingle thrpugh the bars or when bad, a slight miss at high rpms. Not what josh described here.

    So the ktm is fixed?

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  11. #11
    Lifer Pittenger5's Avatar
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    Re: Both smokers down with the same ailment

    Kurlonitis

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  12. #12
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    I don't have a good feel for rich vs lean on a smoker, but I've got far too much experience with detonation from the four stroke world. When it's light, you don't actually feel anything, but it sounds like someone's dragging a screwdriver across the cooling fins on an air cooled cylinder. As it get worse you'll feel the bike stutter and even buck if you push it hard.

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  13. #13
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    I don't know if it's fixed, but it definitely acted better than my earlier test ride. I'll try to get some more rides in to see how it responds.

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  14. #14
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    Re: Both smokers down with the same ailment

    I'm sure you're sick of getting suggestions at random, but I've gone through this on my YZ. I was convinced I had something in my carb, so I cleaned it and it seemed better, but the symptom came right back. Long story short, I cleaned the carb like 3 times and it was finally fixed. I suspect if I had used an ultrasonic cleaner it would have been fixed the first time, but I didn't.

    Good luck!

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  15. #15
    Senior Member capitalcrew's Avatar
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    Re: Both smokers down with the same ailment

    I have no experience with this on bikes but on my race jetski I chased a WOT dying issue forever. In the end it was something in the carb. It also too multiple cleanings to get it straight though.

    Might have had some dirty gas go in both? Running inline filters can prevent this if that happens to be the issue.

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  16. #16
    Lifer
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    Re: Both smokers down with the same ailment

    This sounds more like you are running the bowl low/dry than anything else. I would: clean everything having to do with fuel delivery and tank venting, try raising the float level a bit, replace the needle and seat, and replace any up stream filters you have (including the one on the petcock pickup).

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  17. #17

    Re: Both smokers down with the same ailment



    Or put on a stock carb?

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  18. #18
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    Quote Originally Posted by breakdirt916 View Post
    Or put on a stock carb?
    Why would I want to go even further backwards on runability?

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  19. #19
    Soul Rider Paul_E_D's Avatar
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    Re: Both smokers down with the same ailment

    Quote Originally Posted by gregp View Post
    This sounds more like you are running the bowl low/dry than anything else. I would: clean everything having to do with fuel delivery and tank venting, try raising the float level a bit, replace the needle and seat, and replace any up stream filters you have (including the one on the petcock pickup).
    Float height is another good guess

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  20. #20
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    Float height or fill rate of the bowl was my first line of thought, and I'm going to be investigating that. I was first thinking the needle seat for the float needle might be too small, but that should have shown itself at NHMS. What I didn't consider is the bowl vents could be slightly crudded up which would have a similar impact?

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  21. #21
    Lifer
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    Re: Both smokers down with the same ailment

    Bowl and tank vents are all suspect. Prolonged full throttle under heavy load will push the delivery systems to their maximum capacity.


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  22. #22
    Lifer Imbeek's Avatar
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    Re: Both smokers down with the same ailment

    Sure sounds like a fuel delivery issue. If not a clogged jet or some float problem, are there any fuel filters either inline or part of the petcock that can be cleaned or replaced? Kink, pinch, or melt in the fuel line maybe? Even a clogged or kinked vent line coming out of the gas cap could do it. You checked the airboxes for mouse nests, right?

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  23. #23
    xxaarraa
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    Re: Both smokers down with the same ailment

    float height, bowl vent, fill rate of bowl, needle and seat, 4stroking... all this makes me very glad that I grew up in the fuel injected age. You older generation had it rough with all this crude technology....


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  24. #24
    Lifer
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    Re: Both smokers down with the same ailment

    Try owning a true vintage dirt bike! I discovered very quickly that they are best kept as a fond memory!


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  25. #25
    Lifer Kurlon's Avatar
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    Re: Both smokers down with the same ailment

    25 years old, it's not vintage yet?

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