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Runs, but not quite right!

Discussion in 'XJ Technical Chat' started by Tom Culbertson, Sep 4, 2018.

  1. Tom Culbertson

    Tom Culbertson New Member

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    1986 Yamaha MJ700X Maxim X - - - Had not run for a year before I acquired it. I changed the plugs, cleaned the carbs, cleaned the gas tank, replaced the intake rubbers (from air box to carbs), repaired some wiring issues (unrelated to ignition, charging, etc.) put good gas in it...........voila, it runs! But.....it pulls strong on acceleration, sounds "flat" at highway speed and misses intermittently at cruising speed and at idle. Idles fine once it's warm. The carbs were balanced by a pro and mixture set by him, too. No wet plugs. Battery is fine - 12+ volts, charging system putting out proper voltage. What next? Replace ignition coil? This bike has a lot of miles on it, but I know little about it's history.
     
    Tom Culbertson, Sep 4, 2018
    #1
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The TCI would be the last thing to look at.

    Check valve clearances.

    Describe how you cleaned the carbs.
    How far were they taken apart, and were any parts replaced?
    Were the slide diaphragms inspected?
    Were the fuel levels checked (not just the float heights).
     
    k-moe, Sep 4, 2018
    #2
  3. Tom Culbertson

    Tom Culbertson New Member

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    I removed the carbs, took the upper half off, thoroughly cleaned the lower halves with carb cleaner and compressed air. Cleaned the jets, main needles of slight corrosion, ran air through every orifice, did not disturb the diaphragms other than to inspect them. Replaced no parts. The carbs were actually very clean except for some green corrosion in the jets, which I removed. I did not check the float heights.
    I don't think the "miss" I'm getting is a fuel issue. It's too intermittent/irregular. I did not check the valve clearances. I don't know how, other than to read a manual. I'm not a pro at this.
     
    Tom Culbertson, Sep 4, 2018
    #3
  4. Polock

    Polock Well-Known Member

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    start it up, go for a ride till it's warmed up. park it but leave it running and spray some water up on the coils and plug wires with a spray bottle.
    see what happens?
     
    Polock, Sep 5, 2018
    #4
  5. Mototimothy8

    Mototimothy8 Member

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    Did you by chance take the emulsion tubes out and clean them? They tend to become caked up if they sit without fuel stabilizer in the fuel.
     
    Mototimothy8, Sep 5, 2018
    #5
  6. Polock

    Polock Well-Known Member

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    could be something silly like the side stand switch
     
    Polock, Sep 5, 2018
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  7. alFrumpus

    alFrumpus Member

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    Last edited: Sep 6, 2018
    alFrumpus, Sep 6, 2018
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    cgutz likes this.

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