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HELP!!! Carb rebuild? Starter issues?

Discussion in 'XJ Technical Chat' started by hdelong2002, Aug 3, 2008.

  1. hdelong2002

    hdelong2002 New Member

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    First, thanks for all of the support so far. I feel like progress is being made.

    As a newbie, this site has a lot of great resources.

    Now, here is where I stand:

    1) Put in new battery.
    2) Used PB Blaster & Marvel Mystery Oil
    3) Confirmed spark plugs spark
    4) Checked compression (plugs out/throttle wide open)
    5) All 4 cylinders are at 110 PSI

    Recommendations????

    By the way...I have the Haynes Reference book...
     
  2. Gamuru

    Gamuru Guest

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    I guess to answer your question, we'll need to know where you're at with your bike, where you're trying to get to, and what it is that's preventing you from reaching your goal.

    Elaborate, please.
     
  3. randall68

    randall68 Member

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    Does the bike run, Gamura is right, not much to go on unless we know what problems exist??
     
  4. hdelong2002

    hdelong2002 New Member

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    sorry....here goes.....

    The bikes doesnt start, but with some starter fluid blown thru air filter it makes an attempt. Without starter fluid, it just keeps turning over and then after 10-12 tries, I stop.

    Last year when the compression was done, it was at 40-50, but with the help of this forum, the cylinders are now all at 110 PSI. Estimate was $1K to fix. Offered to "junk" the bike for me for free. I kept it and hoped it could come back to life.

    My goal is to get this bike running enough to be an everyday driver, so that I can ride back and forth to work, mainly. My wife wants to ride it also, so I need it to be reliable enough for her to ride also.
     
  5. wizard

    wizard Active Member

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    how did you get the compression up from 40 to 110, which is way below what it should be (156 nom), but would still run if you have, fuel, spark, timing right.
     
  6. RickCoMatic

    RickCoMatic Well-Known Member

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    hdelong:

    Do a "Wet" Compression Test.
    Put 2 tablespoons of Marvel Mystery Oil down in each of the Spark Plug Holes and do another Compression Test.

    Be sure all the Plugs are out.
    The Battery FULLY Charged.
    And most importantly ...
    The THROTTLES Wide Open.

    Let's see what happens to those numbers with the Oil added to the Holes.
    Also ...
    Keep an eye on the Gauge.
    Let us know if the Pressure HOLDS or loses Compression gradually or quickly.
     
  7. hdelong2002

    hdelong2002 New Member

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    I used the advice from this site to use PB Blaster & Marvel Mystery Oil...let sit, then retest with plugs out, throttle wide open...have done that 2-3 times since April....


    Last year, when it wouldnt start very well, I took it in for a tune-up.
    I am convinced that the shop I went to last year, just looked at the bike as an '81 and didnt want to spend time trying to determine what it really needed. They repair wrecked bikes (salvage shop) so I figured they might be able to help, but kind of think that an '81 was past their limit.
     
  8. Gamuru

    Gamuru Guest

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    Assuming the engine compression is fine, your carbs need work, especially if it will try to fire with starting fluid. You're going to want to get those carbs cleaned. As for getting the bike to start on choke, see my how to on cleaning the enrichment circuit well.
     
  9. RickCoMatic

    RickCoMatic Well-Known Member

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    You've got some tough decisions to make.
    You can try cleaning the Carbs and trying to make the bike run; but those Compression numbers aren't good!

    Bikes with low compression numbers usually go downhill pretty quickly.
    Whatever is the cause of the low compression gets worse after the engine is running.

    Before the situation gets so bad that it will cost you a whole lot more to rectify it; I'd concentrate on doing something about getting some compression back.

    Right now, before anything bad happens, you have the opportunity to save the engine from incurring any serious damage that could result in a mechanical breakdown that could ruin the engine.

    Compression is what puts the brakes on the Piston from keeping going in a straight line up through the top of the Cylinder Head.
    The Compression slows the Piston's inertia.
    Combustion reverses the direction and completes the power stroke.

    When Compression numbers are low there is less less force to reduce the inertia and the Connecting Rod bears the full responsibility of stopping the ascent and reversing the direction.

    Continued stress on the Connecting Rod without adequate Compression to help reduce the upward force of the Piston causes fatigue on the Connecting Rods which leads to a Connecting Rod failure.

    Inevitably!

    Either you do something about it ... now that you know; or the Rods (all 4)
    are going to be exposed to the undue stresses I mentioned earlier and a catastrophic failure is likely to occur.

    You probably need Rings (and/or) a Valve Job.
    I don't see that putting time and effort into trying to get the Bike running decently without addressing those facts would be a wise decision.
     
  10. hdelong2002

    hdelong2002 New Member

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    Can a newbie do the Rings and/or Valve job? I'm willing to try to learn to take of this thing. Or is it really a job for the experienced mechanic, because some things just need done by know-how?

    I have the Haynes reference book also...
     
  11. RickCoMatic

    RickCoMatic Well-Known Member

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    Doing the Rings and Reconditioning the Head is straightforward Small Engine work.
    If you haven't been down that road; Id get some help.

    I'd get creative to save some time and money.
    Contact your local Technical High School and speak to the Department Head of the Auto Shop.
    Tell him of you dilemma and see if he or one of his most talented students would provide some of their expertise and experience to help you.

    Explain to them you'd like to have an expert help you with installing some new Piston Rings in your Vintage Yamaha.
    Be sure to mention you have the Workshop Manual.
    Suggest donating some money to their "Expendables Fund" and offering a modest amount of a gratuity for the help you desperately need.

    Offer them the "Opportunity" to use your Motorcycle Engine as a "Project" for the Class to use their collective skills in assisting you with the restoration.

    50-50

    Either they say: "Yes, we will."
    -or-
    "Sorry, we can't help you."

    If they tell you NO ... ask him for the name of one of his most talented students he would recommend to you to contact privately!

    Go for it.
    You got absolutely nothing to lose!!!
     

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