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  1. #1
    PolarisNut's Avatar
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    1.5 N/S...any fuel flow issues?

    This isn't a Yamaha specific question, but know you guys have experience here. The problem I'm having is fuel is leaking from the booster at lower RPMs where the motor vibrates badly. I'm running 2.0 N/S w/ a 115g spring. I was thinking of trying a 1.8 or even a 1.5 N/S to try to get it to stop, but some feel that it wont feed the motor under heavy loads. I know you Yami guys do this all the time. Just looking for some feedback. Carbs are Full Spectrum 48mm with two external fuel pumps, BTW. Brazina says to try a 1.8...I guess he ought to know, as they are his carbs. This is on a tripple pipe 1200 Poo, BTW.


  2. #2
    All hail the Chief! fullboogie's Avatar
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    I've heard of this before with 2.0's. 1.5's have been successfully used on skis going 80+, so they will probably be fine for you. Consider switching, and installing the proper springs and setting popoff.

    Oops - just realized this isn't a GPR. Never mind...

  3. #3
    PolarisNut's Avatar
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    Quote Originally Posted by fullboogie View Post
    I've heard of this before with 2.0's. 1.5's have been successfully used on skis going 80+, so they will probably be fine for you. Consider switching, and installing the proper springs and setting popoff.

    Oops - just realized this isn't a GPR. Never mind...
    No, its not for a GPR, but if 1.5s flow fine on an 80+mph GPR, they should be fine for me trying to reach 70 on my lowly Polaris

  4. #4
    cheatin' piston popper addicted's Avatar
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    Nut, did you try calling full spec?

    http://www.fastcarbs.com/

    and if it matters, I think a 1.5 will be fine as well.

  5. #5
    PolarisNut's Avatar
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    Quote Originally Posted by addicted View Post
    Nut, did you try calling full spec?

    http://www.fastcarbs.com/

    and if it matters, I think a 1.5 will be fine as well.
    Getting ahold of Ed is not easy, but I did finally speak with him the other day. He says to try 1.8s, new check valves, but don't double up on them, and make sure their sealing surface is lapped. I trust what he says, but then again, I trust Randy at Watcon, and he says they are too small.

  6. #6
    Duke's Avatar
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    1.5s would be fine as far as flow goes but you would have to readjust your popoff. Have the 2.0s been sitting for a while? The needles can get a wear ring in them not shutting the fuel all the way off, especially with the 115 gram springs. If so it may just need new needles to get the dribbling under control.

    Most tripples will knock a a little fuel out at idle due to the vibration, usually doesn't hurt much.

    Another thing to try would be doubleing the check valve on the kidney.

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