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Pretty spectacular screwup on the 750

Discussion in 'XJ Technical Chat' started by JPaganel, Sep 22, 2012.

  1. JPaganel

    JPaganel Well-Known Member

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    I don't know exactly what it is that I did, but I had a pretty spiffy moment there last night.

    I got new brake hoses and finished putting together the brakes. A few days before that I reinstalled the cleaned carbs, had some trouble with a sticky throttle cable and lubed it.

    So, after getting it all together I decided to start it up. Choke on, bike starts, idles up, choke off, RPM keeps climbing. It settles at about 5000 and backfires a little. I start messing with idle screw, that does nothing. I let it run for a few minutes, while poking around. And then I happen to look at the header. #2 and #4 pipes are starting to glow.

    Turned it off right quick.

    Haven't tried to figure it out yet, so I don't really know what the problem is, but red hot exhaust is pretty spectacular.
     
    JPaganel, Sep 22, 2012
    #1
  2. jeffcoslacker

    jeffcoslacker Member

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    That's what mine did a while back....don't know if the pipes got that hot but they did tint a bit gold after that episode.

    Could not figure out what went wrong to save my life.

    I took the carbs off again, tried to spot the problem and decided I couldn't find it, put them back on and it's been fine since.

    Glad it stopped. But wish I knew what I did wrong.
     
    jeffcoslacker, Sep 22, 2012
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  3. JPaganel

    JPaganel Well-Known Member

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    I have some kind of an aftermarket exhaust which is black, so it's more noticeable.
     
    JPaganel, Sep 22, 2012
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  4. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    The two pipes that are turning red means that your mixture is so rich it's burning in the exhaust headers.
     
    MN-Maxims, Sep 22, 2012
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  5. LVSteve2011

    LVSteve2011 Member

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    I used to watch the exhaust pipes of my BMW glow red, could only see it at night and I was at full throttle. Guess it was just the nature of my bike to do that, didn't cause any damage.
     
    LVSteve2011, Sep 23, 2012
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  6. JPaganel

    JPaganel Well-Known Member

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    Sounds right. I think I might need to re-check floats and bench sync.
     
    JPaganel, Sep 23, 2012
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  7. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    The older BMW's exhaust, like the pipes on my Norton and most aftermarket systems, are single-walled and therefore directly show the effects of heat or overheating.

    The stock Yamaha pipes are double-walled so you don't see the effects of heat unless they get WAY overheated, or the inner pipes crack or rust.

    I'd be more concerned that those cylinders were running lean and therefore too hot.
     
    bigfitz52, Sep 23, 2012
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