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I think I have a carb issue...

Discussion in 'XJ Technical Chat' started by Eric Hughes, Oct 14, 2020.

  1. Eric Hughes

    Eric Hughes Member

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    Its been a few weeks since I was on the bike and it has been laggy at low RPM since I acquired it, but ran good enough. Today it was extra, not great. Had to keep bumping the throttle so it wouldn't die at stops. On the road anything over 5000 was great, so of course I kept on it. Giving it a once over back at the house I notice carb 4 has fuel varnish on the outside of the bowl, all the others don't. So I think I have a carb issue, what do you think. Gasket leak at the least. Guess its time to take them to church, check the valves, replace the head bearings, fix the fork seals,, etc..... Oh and pretty sure there is a minor air leak in one of the intakes. Happy Fall to me. IMG_2387.jpg
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    check your spark plugs and charging system too. try to avoid tunnel vision when looking into issues
     
    StahlMaster and k-moe like this.
  3. Eric Hughes

    Eric Hughes Member

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    Plugs look ok at the moment but you are right I do need to check it all out. That #4 cylinder takes a bit to get warm some times. So there are issues, several of them. Just hate to take off too many bits when it does run well enough for a weekend ride through the country. So it will be one thing at a time, till it gets colder than I'm willing to deal with.
     
  4. k-moe

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

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    Start with finding the vacuum leak (or leaks) then, as well as checking valve clearances. She may not have many more weekend rides in her otherwise.
     
  5. StahlMaster

    StahlMaster Active Member

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    I would drop the bowl on that carb and check the float. If you can remove the float, clean the valve seat. May be a easy fix.
     
  6. k-moe

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

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    Temporarily....
     
  7. Eric Hughes

    Eric Hughes Member

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    Valves are pretty much top of the list. With carbs right behind. PO claimed rebuilt and sync but who really knows. While they are off I will get a better look at the intakes for repair or replacement. Funny thing is I bought this bike as a regular rider and parts swap and test for the other project bike (81 midnight maxim). Guess thats how it goes sometimes, that bike moves to the back for a bit. I would get a new bike to be the daily but nothing new really does it for me like these XJs do.
     
  8. k-moe

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

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    You won't find any vacuum leaks that way. The intake boots can have visible cracks and still not have leaks. Brand new intake boots will be crack-free and can still have leaks at the manifold gasket. The throttle shaft seals are a common source of vacuum leaks. The vacuum caps and vacuum line for the petcock can leak.

    Check using carb cleaner with the bike idling without enrichment. Methodically (and slowly) spray the intake boots, vacuum caps, vaccum line for the petcock, and throttle shaft seals. If the engine speed rises you've found the leak.

    Diagnose first. Tear-down later.
     
  9. Eric Hughes

    Eric Hughes Member

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    It doesn't idle consistently without enrichment. Will it diagnose the same if I turn the idle screw up enough to keep it running? Was thinking I needed to go through the carbs to get the idle worked out and fuel flow correct and then sort the vacuum out. Kind of a chicken and the egg situation.
     
  10. k-moe

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

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    It will diagnose the same. Adding more fuel (carb cleaner in this case) after the carbs will always cause the engine speed to increase. The enrichment may be masking a vacuum leak, and the carbs may otherwise be working well (aside from the leaky float bowl).
     

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