surge at steady throttle

Discussion in 'Sportster Models' started by trat, Nov 11, 2012.

  1. trat

    trat Member

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    Ok getting my new, to me, sportster running pretty good now thanks to the help of you guys on the forum. I now have one more thing that bothers me. That is when riding at a steady pace say 50mph it gets a slight surge. Just enough to be annoying. To review....my bike is a 2000 1200XLH with a Mukini HSR carb. Since I have had it (about a month now) I have had idle problems which I cured with a rejet and adjustment of the pilot air screw. I also had trouble with the carb overflowing which was cured with a new float needle and float level adjustment. Also had some brake problems which were taken care of by a brake fluid flush. I am wondering if the surge could be related to an adjustment of the accelerator pump or possible vac leak at the intake. Also the VOES switch has been removed from the bike and I don't understand why! Is there some reason why this would be removed? The bike runs great with plenty of power. It starts and runs great but this surge is annoying!
     
  2. Jack Klarich

    Jack Klarich Expert Member

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    Check for vacuum leak first, but you are probably a bit to lean at cruising speed re jet carb?
     
  3. Breeze3at

    Breeze3at Well-Known Member

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    Define your surge. At steady throttle it feels like accelerate, or it falls off a little. I attached a Mikuni tuning PDF if you don't already have it. There are lots of subtle tuning adj. that could be your surge. Some aftermarket ignitions say the VOES isn't necessary. I removed mine ('92 Dyna) for a while, then put it back on. I did notice less pinging under load with voes on.
    http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf
     
  4. trat

    trat Member

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    just not cruising steady seems to accelerate then slow down kinda like a nervous throttle but I don't see any change in rpm or speed so it it very slight but noticeable....I have the tuner guide downloaded already and it was a big help setting up the carb. Could the VOES being gone cause this? maybe timing changing?....I don't understand exactly what it does but I think it's similar to a vacuum advance on an older car, is that right?
     
  5. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    The voes is a vacuum operated electronic switch that passes information to the ignition module to tell it when to advance and retard the ignition timing

    If there is no voes fitted has the vacuum port on the carb been blocked of to prevent the carb from drawing air in

    Brian
     
  6. Breeze3at

    Breeze3at Well-Known Member

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    I just looked at the instruction sheet for my aftermarket (Dynatek) ignition system. It says if the VOES is not used, the purple wire should be grounded to the frame or engine. That gives a steady (early) advance curve.
    My bike is 8 yrs. older than yours and a Dyna, but I think the same principal should be followed. I just looked at a XLH VOES on Ebay and it looks like it has two vac. line connections.
    98 Harley Davidson Sportster Sport Vacuum Operated Electrical Switch Voes | eBay
     
  7. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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  8. tourbox

    tourbox Senior Member

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    Do you have free play in throttle? A small amount is needed.
    tourbox
     
  9. trat

    trat Member

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    Yeah the vacuum port is capped.
     
  10. trat

    trat Member

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    I don't know if I have a stock ignition or if it has been changed to an aftermarket.....If it is stock and VOES has been removed should the wire still be grounded? Or does that just apply to the aftermarket set ups? Also the tank is a larger aftermarket tank and the petcock is not a vacuum type. The previous owner is no help, He really knows nothing about the bike he bought it this way and had it for a couple of years.