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  1. #1
    aquaaddict's Avatar
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    Popoff pressure at 46 PSI ?!?

    Hi,

    Just rebuilding my Mikuni BN44, and upon doing hte popoff pressure test find that is pops at 48PSI using the bright silver spring in the genuine mikuni rebuild kit, so I tried the old spring and that goes at 46PSI.

    However the tables I have seen show that for the 1.5 needle it should pop at 32. I can understand it being a few out, but not this much.

    What can make such a big difference, or is there anyway that it should be 46-48PSI?

    Its a 1995 701 engine (62G) , single carb.

    The ski wasn't running when I got it so I didn't measure it before I pulled the carb apart. Have checked it using 2 different gauges.

    Thanks

    Anthony


  2. #2
    Yamaha artisan Cutlass's Avatar
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    That is quite a bit off. Are you using WD-40 to lube the needle and seat like the Mikuni service manual recommends? They did change the "Gold" 115gram spring to "Platinum" and its hard to tell the difference between that and the silver spring. I believe the 115g spring comes with the rebuild kit and thats probably what you installed. Just for reference, when I did my 3 carbs, I used the 115gram spring and 1.5 NS and came up with 48psi pop off pressures

  3. #3
    aquaaddict's Avatar
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    Quote Originally Posted by Cutlass View Post
    That is quite a bit off. Are you using WD-40 to lube the needle and seat like the Mikuni service manual recommends?
    Yes

    Quote Originally Posted by Cutlass View Post
    They did change the "Gold" 115gram spring to "Platinum" and its hard to tell the difference .... Just for reference, when I did my 3 carbs, I used the 115gram spring and 1.5 NS and came up with 48psi pop off pressures
    Ah ok that could explain it. Although not sure why the old spring also comes in at a similar 46 PSI, could it be that is actually the pop off required? I cant find the actual popoff spec anywhere, but the service manual confirms the current 1.5 needle valve, and 115 and 135 jets are correct.

  4. #4
    Mighty Mouse's Avatar
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    So if 48 PSI is too high, where should it be on a 701?

  5. #5
    aquaaddict's Avatar
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    Quote Originally Posted by Mighty Mouse View Post
    So if 48 PSI is too high, where should it be on a 701?
    Well the part number in the Yamaha parts manual for my engine states part number
    6R7-14253-00-00 which is apparently the 115g spring, which used to be gold colour coded and is now platinum, and seems to be the one included in the Mikuni rebuild kit (either that or it is the silver one thats included, but the silver is the softest one so doubt its that one).

    So guess it maybe the right one all along?!

    Anthony

  6. #6
    Mpeavler's Avatar
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    Stock should be 1.5 N/S and 115 spring.....if it's 100% stock go that route. The color on the 115's did change...be careful one spring looks right but is only like a 60-65 gram spring ...not the 115

    M

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