Yost powertube set up

Discussion in 'Sportster Models' started by Mjolnir, Oct 31, 2012.

  1. Mjolnir

    Mjolnir Member

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    Hi from sunny South Africa,

    I have a 1200 XL Sporty. I installed a Yost Powertube kit on the stock 40 CV carb along with the following adjustments;
    1. Slow jet up from 42 to 45. Main jet up from 170 to 175.
    3. Drilled out the slide needle hole with 1/8" drill bit supplied in the kit. vacuum port already drilled out to 1/8".
    4. Installed the blue needle with the e-clip on slot 3 (factory setting).
    5. Installed slide spring supplied with the kit.
    6. Bike has stock headers but drag tailpipes and SE heavy breather air intake.
    7. Backed out mixture screw to 21/2 turns + 1/8 from seat.

    Bike has improved performance but does not idle smoothly. Questions:
    1. Is this set up correct for altitude 5751 ft (1753 m) above sea level?
    2. Some advice given was that the vacuum port should not exceed 7/64" and, if so, to replace the slide.

    Will really appreciate some advice on this :34:
     
  2. BUBBIE

    BUBBIE Well-Known Member

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    I would be adjusting the idle screw FOR the best idle NOT just out the # of turns you have.

    The larger 42 to 45 Might be the problem... The Higher in altitude the Less fuel (the smaller jet) is needed.. Just one size to a 44 does make a difference here.

    On my 1200R sport at 4400 feet, I needed to go back to the smaller jet from 800 foot elevation where a larger idle jet was needed...

    I have Never had good results on that type of carb change. I like the Stock carb set-up and drilling the slide is a No No in my book... This can make for a bad idle..... Did you go with a lighter diaphram spring? (looks like you did in the kit) I never had good results from that either.

    I have done all that type of stuff on the cv carbs, only to find over the years of Monkeying, a clean, well jeted Stock carb worked the best for me...(older now):newsmile100:

    Just my thoughts here. You'll get more from the sporty riders..Hang in there.

    signed....BUBBIE
     
  3. Mjolnir

    Mjolnir Member

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    Hi Bubbie,

    Thanks for the info. I adjsutedt teh mixture screw until I got a clean blast without hesitation, backfiring or smoke from the pipes or carb.

    Your info mirrors other opinions that I have been able to get from the Internet. Will try a smaller slow jet and fit the original spring along wth a new slide.

    again,

    much appreciated
     
  4. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    I agree with Bubbie here. I have done the same thing only to come back to original configuration and focus on tuning with jet changes and idle/air mixture adjustment. Had to beat this simple carb when set up right.

    Some of the kits are really designed for more of a drag set up where you are going immediately to WOT and holding there through the gear changes. Not the kind of riding most of us do!!

    TQ
     
  5. Mjolnir

    Mjolnir Member

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    Thanks TQuentin,

    Well, suppose it boils down to buying a new slide as both the needle hole and vacuum port holes are at 1/8' . Will put it down to school fees.
     
  6. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Yep. Live and learn. I think we have all done this!!

    TQ