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High Altitude

Discussion in 'CV Performance' started by johnr733, Jun 7, 2011.

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  1. HarleysLR

    HarleysLR Active Member

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    probably a little lean on the slow jet, try a 48, sometimes shimming helps sometimes it don't. I run a 48 in both my bikes and have the same jetting as I had with an EVO with 10.5 :1 compression. I'm at 6,000 ft, the 190 is probably pretty close. Change jets before shimming.
    HarleysLR, Jun 29, 2011
    #21
  3. johnr733

    johnr733 New Member

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    Yes, I know it raises the needle, but what effect does that have on the carb? Why would someone choose to do it, what are they trying to solve by this step?
    johnr733, Jun 30, 2011
    #22
  4. HarleysLR

    HarleysLR Active Member

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    Shimming the needle raises the needle a little and it allows more fuel in at lower rpm, it is a way to mask the main problem of being to lean at low rpm.
    In reality a thinner needle will change the amount of fuel without changing the jetting. The needle from the first (1988-89) 1200 Sportster, Part No. 27094-88. This needle is smaller in diameter (richer) in its straight-diameter section, which controls mixture strength in the 1/8-1/2-throttle range.
    HarleysLR, Jun 30, 2011
    #23
  5. kenfuzed

    kenfuzed Administrator Staff Member

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    Shimming a needle has an effect on all ranges of the needle so before doing so one needs to be prepared for more than a single change. Because the needle has several steps that help transition idle to an off-idle state, off-idle to midrange, and finally midrange to a handoff to the main jet for 3/4-full throttle, all these transitions will move when shimming the needle. Every version of needle has it's own specific profile to address the range in which it is expected to deliver for a particular engine or model. The most common consequence of shimming a needle is that you cure a lean off-idle mixture but the move allows the main jet to circuit to kick in too early, thus creating an overly rich condition before the engine rpm is ready for it. This can sometimes feel like the engine momentarily bogs (not to be confused with a hesitation) as the bike reaches full throttle.

    I am a firm believer that using the proper needle designed for an application is far more accurate than attempting to shift a transition point with shims. There are circumstances where shimming is appropriate but you should know what you are seeking to change and how that will change other areas before throwing a shim on a needle. Adding a shim to only improve the off-idle section is better accomplished by tuning the mixture screw. This is also why I have spent years in developing needles, because needles such as the N65C (1988 XL) were developed to overcome a dead spot on a carb that lacked an accelerator pump, but this same needle may not be the right choice for other models.
    kenfuzed, Jun 30, 2011
    #24
  6. johnr733

    johnr733 New Member

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    Hi again guys, need a little insight here.

    For the first time since installing the kit I had the bike on a relatively steep hill today. Bike started sputtering rather badly and I had to start goosing it to keep it running. Float related? Any other thoughts?

    As always, thanks in advance.
    Last edited: Jul 31, 2011
    johnr733, Jul 30, 2011
    #25
  7. kenfuzed

    kenfuzed Administrator Staff Member

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    Did it sound like it was pinging?
    kenfuzed, Jul 30, 2011
    #26
  8. johnr733

    johnr733 New Member

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    No, not really the description I would have, more like a missing feeling.

    However I would be curious as to what to do if that happened to be the case also.
    johnr733, Jul 31, 2011
    #27
  9. cowboy

    cowboy Moderator Staff Member

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    Just how steep was that hill to make you think it s float related ? I have Been over the mountains of new mexico & not had any trouble from the float in my C V carb , if it your float it's not set right , I would check to see if there's dirt or crud in the float bowl
    cowboy, Jul 31, 2011
    #28
  10. johnr733

    johnr733 New Member

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    It as probably one of the steepest I've ever driven on. The reason i attributed it to the float is because I did adjust it when installing the CVP kit and i felt it was a little tricky. Not sure of myself, you know?
    johnr733, Aug 1, 2011
    #29
  11. cowboy

    cowboy Moderator Staff Member

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    oh now i see I live at sea level & rode all over the mountians of new mexico with no problums , sounds like you float is just a hair off
    cowboy, Aug 1, 2011
    #30
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