help me figure this one out!

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by rockohlic, Sep 29, 2013.

  1. rockohlic

    rockohlic Been here awhile

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    05 950 adv. went on brutal ride, bike went down on rt. side with the tires higher than the handle bars. I couldn't lift the pig so I had to wait 10 minutes or so for the next rider to come along and help up right the 950. In the mean time I did shut of the fuel, however when I tried to start it, it was obvious the bike was flooded so I held the throttle open to clear things out and when it started it back fired thru the carb. Instantly I could tell it was running on one cylinder, at about 2500 rpm it would run on both cylinders and would pop on decal a lot but only at partial throttle openings, at complete throttle closing there was no popping.
    Now I have the bike home with the air cleaner off and at idle there is NO vacuum from the front carb-at all. I can put my hand over the carb opening with no change/ill effect. If I open the throttle it will start to fire on the front cylinder but does back fire thru the carb.
    OK, looks like I jumped a tooth some where. I will get it apart today and do a leak-down test and assuming I did not bend a valve, where do I start looking for the problem?
    #1
  2. Ramv

    Ramv Been here awhile

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    Do you have the emissions still in place ? You may have loaded the charcoal canister with fuel.
    #2
  3. rockohlic

    rockohlic Been here awhile

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    no, all ectomy's performed. I know the chain can jump but how bout the cams? How can I tell which one? am I over looking something simple?
    #3
  4. mdfehrmann

    mdfehrmann Been here awhile

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    The 950's are getting to the age where the carb diaphragms are starting to fail. I've seen more than one at this point so that's an easy check and fix.

    Matthew
    #4
  5. Tangai

    Tangai Been here awhile

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    Sounds like when the bike back fired, it blew the front carb off from its mount.
    #5
  6. Orangecicle

    Orangecicle On a "Quest"

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    Check for any vacuum leak, such as a boot issue as mentioned. If you find nothing, pull the carbs and clean them well. You might have dislodged some trash in a bowl and stopped up your pilot/idle circuit.
    #6
  7. rockohlic

    rockohlic Been here awhile

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    thanks, I will do tonite and report back!
    #7
  8. rockohlic

    rockohlic Been here awhile

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    no vacuum leak. My leak down tester does not have a fitting small enough so this will have to wait till I can get the proper part. sure seems the cam chain jumped. Has anyone had this happened and what did your bike run like when it did? I have read here some where that you never start the bike with the throttle open cause the hydraulic tensioner is not up to psi yet. what say u-guys?
    #8
  9. Sumi

    Sumi Long timer

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    +1 on the carb boot leak.. Are you sure it didn't blew off the carb (or tore the boot)?

    IMO pull & reinstall the carbs (check for cracks on the boot during this, also you should check the front carb at least - as some serious backfire could cause the slide/diaphragm to melt, and as written before it's easy to clog the idle circuit as well), and if it's still producing the problem only then check the timing.

    Also you should check the vacuum ports on the manifold if they are still in place / not leaking.

    If the timing chain jumped (which IMO is quite rare to happen), then - because of the cams are gear driven - both intake and exhaust cams will be off, and you will probably need a degree wheel to readjust it properly.. Should this be the case, play attention to get it right (infos about firing order and proper crank degrees are on ktm950.info) - don't configure it for a bigbang setup:)
    #9
  10. rockohlic

    rockohlic Been here awhile

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    checked all the points of vacuum, even put the carbs back on with out the air box because it is difficult to see all around the boots. One weird thing is the slide on the back cylinder (the only one running at idle) flutters, a lot! it moves up and down rapidly 1/4 an inch. I know crank case air moves this way but.....?
    #10
  11. sstewart

    sstewart Long timer

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    Check that diaphragm closely. I let a bad one deal me misery once.
    #11
  12. renogeorge

    renogeorge Long timer

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    Did you check front cylinder plug? I know you said you have low/no vacuum. But pushing an unexploded mixture through the combustion chamber doesn't produce normal vacuum at the carb.

    Good luck
    #12
  13. rockohlic

    rockohlic Been here awhile

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    just did a leak down test and the front cylinder will not hold any psi. I even loosened the cam towers in case the valves got tight on me and the cam was pushing down on the buckets w/out lobe contact. When blowing air into the cylinder I can feel air coming out of the intake. Burnt or bent valves????
    #13
  14. Zuber

    Zuber Zoob

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    Yes.
    #14
  15. rockohlic

    rockohlic Been here awhile

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    Is it possible to skip the chain on the cam gears if you start the engine with the throttle open(flooded) and the hydraulic tensioner does not have a stiffie yet? I know the "what" now just trying to figure out the "why". And also does anybody have a line on valves or do stick with OEM?
    #15
  16. Sumi

    Sumi Long timer

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    I've never had it happen on my friends (3 of them on lc8s) or my bike, and I can tell you all of them bikes tend to lay a lot on their sides:DD But.. ofcourse it might happen..
    Don't want to ruin your day, but as you probably already know, it seems like you will have to pull at least the head to see what's going on:(

    Btw, is the spark plug/coil OK? (swap it between the cyls? maybe..)
    #16
  17. rockohlic

    rockohlic Been here awhile

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    I did not think a need to, after the leak down test was positive. I also poured alchohol into the intake ports then compressed air into the cylinder=lots of bubbling, lots of air comming from the cylinder up thu the valves.
    #17
  18. Zuber

    Zuber Zoob

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    Unless your cam chain is totally shot - so stretched that it rattles all the time - it can't skip. Even if you pull the tensioner out, you can't get it to skip.

    You've bent or burnt a valve.
    #18
  19. gearheadE30

    gearheadE30 Long timer

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    My money is on a bent valve. If you have enough fluid in the cylinder and try to turn the engine and compress the fluid, if the valves try to open at the same time there can be so much pressure that there literally isn't anywhere for things to go, resulting in excess pressure on the valve stem, usually causing it to bend. If it was broken, you'd hear bits of valve grinding away in your engine, usually.

    If it's flooded really bad, you can often put the bike in 6th and push it backwards to try to blow things out. Due to valve overlap and rotational speed, this is often more effective than using the starter if things are really bad.
    #19
  20. rockohlic

    rockohlic Been here awhile

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    I do not think it was flooded enough to fill the cylinder. I appreciate Zuber's enthusiasm for the burnt valve theory. Good to know it is that hard to skip a tooth on the cam chain. FYI the 950 has 21k miles. I am the 2nd owner and when I got it I immediately adjusted the valves and found the intakes very, very tight. I just do not want to replace the valves with out having a good feeling it is not going to happen again. weird thing is I put 2000 miles on it after adjusting the valves and then ........heads are coming off tomorrow.
    #20