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Thread: Carb tuning.

  1. #1
    PWCToday Regular Firebird!'s Avatar
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    Carb tuning.

    I am rebuilding the motor from Yamaha SUV (65u non pv). Had to mail the top end to have the sleeves bored since could not find anybody local to do the job. In the mean time, while waiting, decided to go through the carbs.

    Long time ago, when I purchased the ski, the carbs were trashed from the salt water corrosion, so I got other set of carbs from eBay. They look exactly identical except they came with smaller size fuel nipples. Don't think it should be a problem , but have to use smaller fuel line on a carbs and then transition it back to larger one to go out.

    I remember that I put in the new Jets and needle and seats. I do not remember why I chose those sizes so I wanna verify that it is correct choice for my setup.

    I do have K&N Air Filters on top of carbs with chokes still present.

    Mag:
    HS Jet 140
    LS Jet 102.5
    N/S 1.5
    Pop Off 28 Psi (I don't know why is it so high and differs from other carbs)

    Center:
    HS Jet 140
    LS Jet 92.5
    N/S 1.5
    Pop Off 21 Psi

    Pto:
    HS Jet 140
    LS Jet 100
    N/S 1.5
    Pop Off 20 Psi

    So, is this a correct setup or I need to change anything?


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  2. #2
    PWCToday.com Is My Home Away From Home
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    Re: Carb tuning.

    Throw your kn filters in the trash and get new ones. Look up the 65u balance mod on greenhulk and do it if you want your carbs correct.

  3. #3
    Thinks everythng sux =) Top Dog vomitspot's Avatar
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    Re: Carb tuning.

    be sure to inspect fuel pump check valves
    those are the little clear circles about the size of a dime
    Last edited by vomitspot; 07-17-2017 at 10:58 AM.
    nina hagen daz

  4. #4
    PWCToday Regular Firebird!'s Avatar
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    Re: Carb tuning.

    Quote Originally Posted by driftmaster View Post
    Throw your kn filters in the trash and get new ones. Look up the 65u balance mod on greenhulk and do it if you want your carbs correct.
    Why would I throw my filters in a trash and spend around $200 on new ones? I know they may not be the best on a market, but I think they worked good in a past.
    By doing balance mod you mean is when they drill out The Return orifice from all three carbs and install a jet in return fuel line as restrictor?

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    Last edited by Firebird!; 07-18-2017 at 12:02 AM.
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  5. #5
    PWCToday.com Is My Home Away From Home
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    Re: Carb tuning.

    Yes drill out returns.

    Put the stock air box on then it will make more power. KN's are junk, you dont need a papor filter, just a screen. KNs are very restrictive, unless you have one I haven't seen before throw it in the trash and go stock
    air box. I guess you could try to sell it.

  6. #6
    PWCToday Regular Firebird!'s Avatar
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    Re: Carb tuning.

    Quote Originally Posted by driftmaster View Post
    Yes drill out returns.

    Put the stock air box on then it will make more power. KN's are junk, you dont need a papor filter, just a screen. KNs are very restrictive, unless you have one I haven't seen before throw it in the trash and go stock
    air box. I guess you could try to sell it.
    I don't think it is paper - I'll take a picture when I'll get home tomorrow. What Jets/pop-off's should I have if I'll decide to go with stock box?

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  7. #7
    PWCToday.com Is My Home Away From Home
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    Re: Carb tuning.

    43 pop off anything less and it will load up at low rpm's witb135 high and 105 lows. Cross over fill on each side of the intake is also recommended and like vomitspot said check your pump side check valves and double up on the siphon valve.

  8. #8
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    Re: Carb tuning.

    Tap the last return for the jet too, that way the mod stays with the carbs.

  9. #9
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    Re: Carb tuning.

    Quote Originally Posted by driftmaster View Post
    Tap the last return for the jet too, that way the mod stays with the carbs.
    Cant do that - like I said my nipples a bit smaller on those carbs and jet will not fit inside - will have to do it outside.
    Last edited by Firebird!; 07-18-2017 at 05:28 PM.

  10. #10
    PWCToday Regular Firebird!'s Avatar
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    Re: Carb tuning.

    Ok here is the pics of my k&n filters. They do not look to be too restrictive to me - I can clearly see through them. In my opinion the stock box would be definitely more restrictive.
    IMG_8953.JPG IMG_8954.JPG IMG_8956.JPG IMG_8955.JPG

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