HELP! Vibration problem

Discussion in 'Dakar champion (950/990)' started by crazybrit, Jun 12, 2011.

  1. Chuckracer

    Chuckracer Jerkus Maximus

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    It's not set-up to fire as a "twingle", is it?
    #81
  2. crazybrit

    crazybrit Long timer

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    It's running on both cylinders if that's what you are asking. Now, whether there is a slight cylinder imbalance is another question.

    I've put about 1200 miles onto the bike since my last post. It's still vibrating a fair bit but it's now at least tolerable with the OEM triple clamps reinstalled.

    Previously I felt it wasn't running well when I'd get back to the city at the end of a ride. Recently I rode up Hwy 58 here in Oregon which climbs from 1200' to 5000' and it felt like the bike ran significantly better at 5000' and (I think) smoother also.

    Ken (Mortimer Sickle) and I went on a long ride again yesterday and we both agree that my bike vibrates significantly more than his, you can feel it above 4000 rpm coming through seat, bars, pegs and tank. Coming back from yesterdays ride for 70 miles at sea level (mid 80's temps) the bike didn't feel like it was running well, hard to explain, kind of a 'loose' not quite pulling hard enough sensation in top gear at 75mph.

    Jetting is same as it was when I got the bike in 2007. Stock with the needles moved one clip for the FMF. I've tried it with and without the Uni Prefilter. I've had the carbs apart more times than I can think of, I just took them apart a month ago to carefully examine diaphragms and needles. The fact that it runs better at altitude and in cooler temps both point to the jetting being too rich but I'm having a hard time believing that this is responsible for a pretty profound vibration change unless it's significantly affecting just one cylinder.

    Someone suggested I take it to the PIR on 9/19 as 2wheeldynoworks will be there and could probably check it out for the baseline $50 rate. I've never had a dyno tune done before, concern is whether he'll be able to check each cylinder.

    Other options at this point seem to be:
    • welding a couple of O2 bungs onto each cylinder and buying/borrowing an O2 tester.
    • seeing if I can get anything interesting test results using the EGT plugs or try some kind of IR thermometer. I'm skeptical of the IR thermometer as I think I need to put the motor under some form of load.
    • buying/borrowing a set of carbs. I borrowed a set before from Head2Wind but it was winter and I just ran it on the side-stand based on the dealers comments about blurring of mirrors being an effective test, stupid of me.
    #82
  3. MortimerSickle

    MortimerSickle Semi-Adventurer

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    ^This seems to contradict.

    Running better at altitude would indicate a lean mixture, and running better at cooler temps would indicate a rich mixture.

    In any case, in my unsuccessful attempt at jetting my carbs, I have been too rich, too lean, and too lame. None of these conditions have caused the bike to vibrate any more, or any less.
    #83
  4. crazybrit

    crazybrit Long timer

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    You need a leaner mixture at elevation as there is less air. I deduced from this that if the bike is therefore running well at elevation it's running too rich at lower altitudes but as you point out, that's boneheaded, the opposite would be true :baldy I need my morning coffee :D

    Yeah, the only case where I can see that it could be causing the vibes is if it's significantly affecting just one cylinder. I still wonder if it's something else inside the carbs, I have no idea what however.

    If anyone has a spare set of (known good) carbs they'd loan, or knows of a low-mileage set being sold *cheap*, LMK. I'm suspicious of higher mileage sets as I've read lots of problematic diaphragm reports and I don't need to be chasing after yet another problem.
    #84
  5. MortimerSickle

    MortimerSickle Semi-Adventurer

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    I would suggest you inspect the diaphragms, regardless of mileage. Mine are 10 years old, have 57000 miles, and still look good. On the other hand I have heard of newer, lower mileage ones that have cracked.
    #85
  6. crazybrit

    crazybrit Long timer

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    See two posts ago, regarding carbs: "I just took them apart a month ago to carefully examine diaphragms and needles".

    My resident mechanical engineer was there when I checked them, we both looked them over with a magnifying glass and flashlight.

    We couldn't see anything. Doesn't mean there isn't a problem of course.
    #86
  7. MortimerSickle

    MortimerSickle Semi-Adventurer

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    I meant, for you to examine any that you were considering for purchase.
    #87
  8. crazybrit

    crazybrit Long timer

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    Ah. I see. That's going to be tricky if they are not local.

    Maybe buying an 07+ wiring harness, FI parts and fabbing up a fuel pump isn't that bad of an idea :D Talk about a wild hair brained tangent :lol3
    #88
  9. MortimerSickle

    MortimerSickle Semi-Adventurer

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    Fixt. :D
    #89
  10. crazybrit

    crazybrit Long timer

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    Too sad to see the last post above be from Ken (MortimerSickle).

    So I "fixed" the issue this summer. I have a 3yo and a 5yo so I've been not riding much in the last 5 years. Plus a bit of the 'throw bike in corner under tarp and forget' issue.

    A long while ago I bought some carbs from another inmate here who himself purchased them to diagnose an issue he was having. The carbs fixed the issue for him (he ended up swapping parts until he narrowed down what the faulty carb part was, diaphragm iirc, replaced that into his original carbs and sold the spare set onto me).

    I've put about 900 miles now on the bike and it seems to be running fine. What's wrong with the old carbs I cannot say, I've disassembled them at least 3 times looking for an issue. Could be diaphragm. Maybe if I get really bored I'll try and figure it out.

    This Winter I plan to pull the 04 motor (I got from eldon, ~24k miles on it now), put my original 06 motor back in (11k miles) and if it's running ok, sell the 04 motor. Hopefully 6 years sitting on garage floor (all openings sealed) hasn't damaged the 06 motor.

    Take it easy up there Ken. You're greatly missed.

    [edit: it's weird reading back on this thread as I'd forgotten Head2Wind had loaned me a set of carbs previously. I remember it was middle of winter and the bike wasn't titled/insured so I was just pissing around comparing the loaner carbs to original ones at 6k rpms on the center stand. IIRC I'd decided that the vibration in the mirrors was somehow demonstrating the issue, which I think now was probably a massive red-herring. For sure just remembering back on this makes my head hurt]
    #90