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  • Carb tuning info

    Since I am STILL trying to eliminate the mid range stumble/sputter that plagues my bike, I have been searching for all kinds of carb tuning info. I recently discovered (along w/help from thewiz) that I am running 127.5 mains w/stock 42.5 pilots in my carbs. Stock mains are 115 for 1 & 4, and 120 for 2 & 3. The only intake/exhaust mods I have are a K&N filter in the stock airbox and the Jardine "spaghetti" pipes w/o the crossover tube. ALL mods were done prior to my ownership , except for the PUC wire repair that I did replacing all 4 wires all the way back to the connector.
    Back to the mains: they are bigger than the size recommended per DennyZ's (awesome) calculations, but the plug color looks good, and at WOT it runs like a cheetah w/its a$$ on fire once it gets above a certain RPM (non-working tach, can't tell you exactly where that RPM is). From idle to where I would expect the needle jets come into play, it runs good as well.
    If you are reading this Prom, you mentioned once before how to adjust my "un-adjustable" needles, but I can't find where that was. Would you please explain that to me again? Should I change my mains back down to a smaller size, or will that affect WOT too much? Mind you, I am not a triple digit rider (planedick ), but every once in a while, I too like to get on it a bit if I'm fairly sure that Jon and Ponch aren't around. I just want it to run like it used to when I first got it.
    Anyway, check this link out. It's got some really good info, even if it's not talking about our beloved BS34's. Any input in the right direction is, as always, greatly appreciated.



    Hi...my name is Mike, and I'm a lane-splitter.
    '80 XS1100SG (mine)
    '87 CMX450C Rebel (daughter's first bike)

  • #2
    Have you done a WOT plug chop? If the plugs have a good color when you check them after WOT then your mains are the right size. The way I understand it you have to tune from the "top" down. So if your mains are good then you adjust the needle up and down until you have good power.

    The way to adjust the "unadjustable" needles is to get some washers (thinner is better) the same diameter as the needle clip and then place the washers under the clip to raise the needle.
    1979 xs1100 Special -
    Stock air box/K&N Filter, MAC 4-2 exhaust, Bad-Boy Air horn, TC fuse box, Windshield, Soft bags, Vetter Fairing, Blinkers->Run/Turn/Brake Lights, Headlight Modulator, hard wire GPS power

    Short Stack - 1981 xs1100 Standard - lowered for SWMBO.

    Originally posted by fredintoon
    Goes like a train, corners like a cow, shifts like a Russian tractor, drinks like a fish, you are gonna love it.
    My Bike:
    [link is broken]

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    • #3
      http://www.xs11.com/forum/showthread...light=Shimming

      http://www.xs11.com/forum/showthread...light=Shimming

      SanDiegoMike:

      Look at the cited threads for shimming needles

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      • #4
        So what has changed since it was "running good"?

        Whens last time air filter cleaned, valves checked etc...?



        mro

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