99 XT600 Severe popping under acceleration

Discussion in 'Thumpers' started by Pursang, Jun 19, 2013.

  1. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
    Jul 15, 2006
    Oddometer:
    107
    Location:
    Okanagan. Canada
    Last couple rides the bike has been popping severely through the carbs, starts around 3500 rpm and up and is getting worse, it pops five or six times each time I start getting on the gas and with each pop it momentarily kills the power, not like a fuel starvation bog but requires gearing down to get up hills, no popping on decelartion, bike starts and idles perfect, valve clearances are all up to spec, plug looks fine, compression is 159, fuel flow is good, I'm thinking it might be electrical since I dismantled/cleaned the carbs only 2500km ago when I installed a new top end. my question is if it's electrical which is the most likely part to cause this ? don't have a lot of cash so I'd really like to get it right, any suggestions are welcomed and appreciated !
    #1
  2. BIG ED XT FAN

    BIG ED XT FAN Long timer

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    Feb 18, 2006
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    1,261
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    Finger Lakes Western New York
    Plug Cap? or CDI unit?:eek1:eek1:lol3:lol3
    #2
  3. damo2010

    damo2010 damo

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    May 26, 2010
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    I know u prob checked this, do u have a lge breather out top of the carb and is it routed correctly. This hose kills mid range revs similar to what your talking about
    #3
  4. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
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    Okanagan. Canada
    Plug caps looks good, not sure yet about the CDI still looking into it.
    #4
  5. Pursang

    Pursang Bultaco !!!!!!!!!

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    Yup if you mean the hose from the secondary diaphragm to atmosphere it's clean and tucked away in a safe place under the seat.
    #5
  6. thumpthumpthump

    thumpthumpthump Thumpthumpthump

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    Is the choke all the way off? thumpthump
    #6
  7. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
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    I'm pretty sure it is, the bike starts, idles and runs perfect except for this popping which starts at about 3500 rpm.
    #7
  8. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
    Jul 15, 2006
    Oddometer:
    107
    Location:
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    Well the search is back on, I pulled the carbs and gave them a thorough cleaning, inspected every part except the coasting enricher and didn't notice anything obvious in the secondary carb, threw the bike back together and went for a short snort only 5 minutes into it the bike was popping like crazy, it seems to be getting worse with each ride cause on the previous ride it took half an hour to begin popping this bad, I'm wondering if it's an electrical issue ? would appreciate any suggestions.
    I noticed the carb was sucking unfiltered air and discovered the original hose clamps even when bottomed out were not clamping tight enough, didn't take much effort to pull the rubber boot off the carb, will use another style of clamp that tightens more.
    [​IMG]
    #8
  9. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
    Jul 15, 2006
    Oddometer:
    107
    Location:
    Okanagan. Canada
    To eliminate a few more possible problems I drained the fuel tank/carb, pulled both of the fuel petcocks off the tank, removed the screen tubes and blew everything clean with compressed air, the screens were surprisingly clean and the tank only had a few grains of sand inside, refilled with fresh premium and installed another spark plug, hit the magic button and no spark now I'm wondering if this issue is related to the original popping under acceleration problem ? any and all help would be appreciated with what to do next !
    #9
  10. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
    Jul 15, 2006
    Oddometer:
    107
    Location:
    Okanagan. Canada
    Here are the results of some testing with an Ohm meter. I would appreciate any suggestions as to what to check out next, should I have the Ignitor checked out if I can find a service that does that ?
    Ignition coil, primary: 4.5 (spec is 4)
    Ignition coil, secondary: 14.0 (spec is 13)
    Stator coil: 0.6 (spec is 0.65)
    Pickup coil: 243 (spec is 230)
    Sparkplug cap: 00.0 (spec is 10k)
    Sparkplug wire: 00.0 (spec ?)
    #10
  11. damo2010

    damo2010 damo

    Joined:
    May 26, 2010
    Oddometer:
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    Location:
    Roma, South Western QLD Aust
    Do you have spark back yet?
    I've been told that the high voltage stuff can be problematic, not sure if you have changed any of the spark plug leads and cap.
    From one of your previous posts, seemed like the popping was starting once bike was warmed up, maybe elec connections are getting worse with heat.
    I'm no expert with this side of it, but maybe sounds like week spark?
    #11
  12. Pursang

    Pursang Bultaco !!!!!!!!!

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    Location:
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    Nope no spark at all, I tried another plug wire and cap from a set of automotive wires I had in the shop, they don't have the copper wire like the original but still I thought it would do if the plug wire/cap were the problem, still no spark.
    #12
  13. motomike14

    motomike14 Thumper Crusader

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    Florida
    Automotive stuff will likely have a higher resistance, which is no bueno on that ignition system.

    Would start simple; test output from stator first then work your way up to the coil to see where the electricity stops at. Like most big bore singles, the Yamaha singles did have CDI issues (black boxes get hot, then boil themselves basically).
    #13
  14. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
    Jul 15, 2006
    Oddometer:
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    Location:
    Okanagan. Canada
    Thanks motomike, can you explain the procedure for checking for juice to the coil ? I set my tester to 200 AC and placed one of each lead to each of the wires going to the coil, turned the engine over but the meter remained at zero, I've searched all over for stator output procedures and numbers going to the coil but nothing is coming up, can't find anything in the various XT600 service manuals I have on pdf files either, I'm probably not testing it right.
    #14
  15. webmonstro

    webmonstro A Aventura Continua....

    Joined:
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    Oddometer:
    731
    Location:
    Portugal
    testing is done by resistance test

    you can build a high voltage spark tester (i did once and it worked) but make sure it's a CDI, since it's a '99 it 's most likely a TCI sistem (uses lower voltage ) i think you can test it with 12 v (not sure)

    As for the popping the 1990-2003 models have two pick-ups in the stator one for low RPM and one for high RPM
    Check the harnesse where the high RPM pick-up connectes to the CDI
    they can sometimes brake (as it kinks on a sharp turn ) where the wire goes in the plug
    I think it's the blue wire

    As for the HT wire to the plug , if you can remove it from the coil just connect a normal copper wire and connect to a spark plug to test output


    more info :

    http://www.transmic.net/en/home.htm



    good luck
    #15
  16. Pursang

    Pursang Bultaco !!!!!!!!!

    Joined:
    Jul 15, 2006
    Oddometer:
    107
    Location:
    Okanagan. Canada
    A great big thanks and congrats to webmonstro you nailed it ! the problem was a broken green/white wire going to the TCI.

    This photo was taken before I started testing components, the green/white wire looks perfectly intact.

    [​IMG]

    After pulling the connector from the TCI the wire popped out.

    [​IMG]

    Broke clean off at the spade connector.

    [​IMG]

    Lengthened the wire by an inch and installed another spade connector, the bike fired up immediately and ran perfect with no popping at all, my thanks to Big Ed, damo, thump, motomike and once again to webmonstro for your help and input, the beast is back ! :D

    [​IMG]
    #16
  17. damo2010

    damo2010 damo

    Joined:
    May 26, 2010
    Oddometer:
    431
    Location:
    Roma, South Western QLD Aust
    Great to hear you got it going. Tis what I love about this forum. This thread is worth saving for future reference.
    #17