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Le Mans IV 1985 no start

Discussion in 'Loop & Tonti' started by thierry roullier, Mar 9, 2019.

  1. thierry roullier

    thierry roullier Just got it firing!

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    I tried to wake up the bike over the past few days after a long winter where this new to me bike started very well. I did change the battery (odyssey). For this I had to move the tank. I removed the cute aluminum air tubes pretending to be air filters and replaced with K/N pod filters as airbox was removed by previous owner. That's all the changes I made. Of course gas pipes were put back in position and locked

    1) engine turns around vigorously when pushing start button
    2) I have good blue/white spark on either cylinders. Spark plugs are on the dark/wet side though
    3) Choke is on and cables system seems to be working
    4) I removed gas cap to ensure no suction issues
    5) gas is flowing and gas is 3 months old

    Yet not even an interest of a start. I removed the Air filters to see if this would make a difference. No luck.
    When I switch the contact off there is a Big Bang

    Any proposed next steps would be greatly appreciated! thanks. Thierry in Chicago.
     
  2. Trout

    Trout GT Reference

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    If plugs are wet & smell like fuel then the choke slides may be stuck.
    Try this:
    Turn fuel petcocks off.
    Put OLD plugs back in.
    Try starting. Let it crank over a few times then stop, then repeat, then hold the button & let her spin.
    If it tries to fire off then it probably is a fuel issue either choke sticking or possible float/needle valve seat sticking.
    Sometimes if a plug has gotten wet they will not work properly.

    Remove air filters & get a can of spray carb cleaner & 2 new plugs.
    Install two new spark plugs.
    Leave fuel turned off.
    Turn key on.
    Do a quick spray of carb cleaner in each carb.
    Try starting.
    If it fires on the carb cleaner you have a fuel issue.
    Check choke slides first.



     
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  3. thierry roullier

    thierry roullier Just got it firing!

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    Thanks for pointing me in the right direction. I will try that and report. Bike is still very cold from the Chicago weather. I just got myself a guzziology manual and will read this as well.
     
    Trout likes this.
  4. fireflyr

    fireflyr Cruisin' Guzzisti GT Contributor

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    My T3 was doing exactly the same thing. It had spark, plenty of fuel and would backfire when I let off the trigger. I replaced the Lucas electronic ignition with a new Dyna III with new 5 OHM black coils and it fires on the first try. I think my old coils may have been the culprit.
     
  5. thierry roullier

    thierry roullier Just got it firing!

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    OK I tried option 1: close fuel taps and let it crank. No luck and big explosion.

    Lots of fuel flowing off the carbs so it seems flooded. I cranked again with throttle open to ty as well. No luck

    I could feel the needles moving when accelerating

    I am going with the hypothesis that the carb floats are blocked in the open position so I will check this next.
     
  6. john zibell

    john zibell Moderator Staff Member GT Famiglia

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    If the floats have been sitting in gas for a long period, they may become heavy. On a bike of that vintage, new floats would not be out of the question.
     
  7. fireflyr

    fireflyr Cruisin' Guzzisti GT Contributor

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    If floats were the culprit then couldn’t you turn on the petcocks until the bowls were full, then turn them off. Then go thru with the start. It should at least fire up.
    I’m betting on electrical. What ignition system is installed?

    Funny thing is when I go to start the T3 the dogs run for the hills. I thought I was going to blow the exhaust system apart. When I pull the Lemans out they could care less.
     
    Last edited: Mar 13, 2019
    thierry roullier likes this.
  8. Trout

    Trout GT Reference

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    Try This:
    Leave petcocks off.

    Pull bowls on carbs & let all fuel drain out.
    Replace bowls.
    Install new plugs. IMPORTANT !!!!!
    DO NOT TURN ON PETCOCKS.
    Spray carb cleaner into carbs.
    Crank.
    If she fires & runs then the problem is fuel.

    If she won't run or even try to run the issue is electrical.
    Possible points are needing attention (if the bike has points).
    Bad/weak coil(s) etc..
     
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  9. john zibell

    john zibell Moderator Staff Member GT Famiglia

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    First post, he has blue spark. Later he says fuel is running out of carbs. Floats have nothing to do with turning petcocks on or off.
     
  10. V700Steve

    V700Steve High Miler GT Contributor

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    If you have a Dyna 3 ignition sys, it will spark w/turning on and turning off the key. Don't confuse this w/out of time. I would shine a timing light in inspection hole. If no light shines no spark in wires. I'd get new plugs if they been damp w/fuel.
     
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  11. thierry roullier

    thierry roullier Just got it firing!

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    Success!! Thanks for everyone for answering my question. I did try most of the options above and what finally did the trick was installing new spark plugs. Finally we had some sunshine in Chicago and I was able to take her for a short run.She now runs like a locomotive. I very much appreciated everyone's help in this.
     
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  12. V700Steve

    V700Steve High Miler GT Contributor

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    Now you can show it off at DeKalb breakfast, 1st Sat of the month. Ride Safe
     
  13. thierry roullier

    thierry roullier Just got it firing!

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    Yes no excuses! I will try in April then.
     

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