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Idle question(s)

Discussion in 'XJ Technical Chat' started by Andyam5, Dec 8, 2018.

  1. Andyam5

    Andyam5 Member

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    So when were talking about idle jets on Hitachi 32 carbs, what are we looking at specifically?

    Here's the problem.
    My 650 4KO was bang on, brakes and suspension all sorted, valves done, carbs cleaned (yes, really cleaned), throttle shaft seals replaced, airbox & intake rubbers replaced, fuse box upgraded to the new type etc. etc.
    I don't have any air leaks, float heights were set dry & wet, carbs were balanced and colourtuned. This was all done a couple of years ago, then, for one reason or another it sat in the garage until 6 months ago when I managed to get back on the road

    It starts first time, every time with some choke - hot or cold, pulls like a train, beautiful to ride and I use it almost every day for commuting or just for giggles but I CAN NOT get it to idle properly

    If I turn the idle knob so thet it idles at 1100ish rpm and then blip the throttle the revs drop back down and it just dies, if I then wind the idle knob back in, it has no effect until it suddenly "grabs" and rpm goes up to about 2500

    So, when I'm sitting at lights or whatever, I have to blip it to keep it running, it's not a major problem but just one of those nagging things that sits in the back of my mind, it'd be so good to get evrything perfect

    Anyhow, what I'm asking is, should I be looking at the pilot jets? And if so, what's changed in the 18 months it was sitting idle

    Cheers for any and all advice
     
  2. XJ550H

    XJ550H Well-Known Member Premium Member

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    pilot jets are about the idle check them reclean them and the passages to the mixture screws

    first thing is the idle must be set when bike is fully warmed up. get the bike warmed up with a 10 or 15 mile ride then set the idle to 1100 rpms
    is the idle knob end making contact with the lever?
     
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  3. Colin 85 700

    Colin 85 700 Active Member

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    To note, pilot jet is the smallest jet in the carb (other than choke jet in bowl)
    It is the first to gum up or plug with debris, reclean as XJ550 recommends.
     
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  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    when you remove the carbs check the throttle shaft plates make sure they are centered and not scraping the carb throat. also check to make sure the throttle shaft is working smoothly and not binding
    with the way the throttle shaft linkage works 1,2,and 4 could be binding

    the idle jet circuit consists of the jet and mixture screw with its passages. the mixture screw does have a very small o ring flat washer and spring.
    this link has a nice cutaway of the carbs
    Something New, Something Naked
    and this link explains the carb function
    THE SECRET LIFE OF CARBURETORS

    you should also make sure the throttle linkage (connection to cable) is not binding and that the throttle cable is well lubed

     
    Last edited: Dec 9, 2018
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  5. Andyam5

    Andyam5 Member

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    Cheers fellas
    Yes the idle knob is making good contact, mechanism is all free ie. shaft & butterflies, mixture screws all have spring + washer + O rings in place (and in the correct order)
    I'm guessing something has upset the mixtures slightly even though I ran the carbs dry before storage, tank has no rust and I'm running it with a fuel filter
    I spose I'll have to pull them out again when the weather warms up next year and go through the whole lot again... Damn you ethanol
     

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