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Tuning

Discussion in 'XJ Technical Chat' started by crow, Oct 10, 2010.

  1. crow

    crow Member

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    After pulling the carbs down and putting them back on bike I'm trying to fine tune the mixtures.

    The bike has an after market 4-1 pipeline exhaust. The previous owner had drilled a couple of 25mm holes in the otherwise stock airbox, which I've plugged up.

    All jets are standard as per the factory manual for the HSC33 carbs (assuming no one has drilled them out). Starting from 2 3/8 turns out and when using the colortune plug I really struggle to find a rich mixture (no orange flame) that should start backfiring/popping or die. I'm backing the mixture screw out to where I'm afraid it's gonna pop out and still just a weak blue colour in the plug.

    Should I be looking at larger main jets at this stage or is there something else to do before this?
     
    crow, Oct 10, 2010
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  2. TIMEtoRIDE

    TIMEtoRIDE Active Member

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    Someone can correct me if I'm wrong, but you want to increase the smaller jets 1 - 2 sizes, not the main jets, for the problem you're having.
     
    TIMEtoRIDE, Oct 10, 2010
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  3. wizard

    wizard Active Member

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    Your stock jets should be good, have you checked they are the right numbers? You are happy that the fuel levels are ok?
    2-3/4 turns is too far out, what is the book default?
    I take it you have synced the carbs with that new carbtune? If so, I would give the colour tune the arse & start with some plug chops.
     
    wizard, Oct 10, 2010
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  4. crow

    crow Member

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    Yep jet numbers match the factory manual XJ750RL supplement for all fuel and air jets.

    Synced carbs OK (well OK for an amateur), haven't checked since fiddling with the mixtures.

    OK will research how to do plug chops but will not have an opportunity to play till Thursday night due to other commitments.

    Not sure if I'll get rid of the colortune plug just yet. For a start it's bloody mesmerizing looking at the thing!

    Edit: I was pretty happy with the float levels, all within spec. Only thing that has me worried is whilst the carbs were level left to right they were not level front to back, I've since read conflicting versions of what is right. Levels were taken from the middle of the carb bowl though.
    Haven't read in a book what the correct turn out of the pilot mixture screw is though. They all say don't touch it.
     
    crow, Oct 10, 2010
    #4
  5. Polock

    Polock Well-Known Member

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    my 750's seem to like about 3.25 turns out, then it's tweek till it sounds good
    don't be surprised if you need to go a few bigger on the main for the top end but it shouldn't matter for idle
     
    Polock, Oct 11, 2010
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