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  1. #1

    Question POP-OFF pressure can this be the problem???????

    Hello To all

    So i have a yamaha xl 760 1998 it used to run great but now it doesn't hehehehehe

    The problem is i can go about 1/4 of throttle and all ok still not planning have to wait a little there then go full throttle rpm go up and down a little an the boom 7000 rpm all good runs no problem but if i want to go lets say 3/4 of throttle engine will just die un less i pull a little on the choke then it will hold


    to i think my pop off valve is opening too late what do you think???


    and by the way what would be a good reading for this pop off valve on this pwc ???


    by the way i am 5000 ft above sea level if that matters


    Thanks a lot guys for your help


  2. #2
    It's obviously​ leaning out in the mid as your probably aware. I believe on most carbs you can measure pop off using a small air gauge and pump. Obviously you have to take them out of the ski.

    Has it always done this or is it a recent development?

    Edit: just saw your 5000 MSL, that means your definitely running lean as there is considerably less oxygen at that altitude to begin with. You should be running rich.

  3. #3
    OK in the multiple test i have made i have been turning the low and the high speed screw alot and what i have accomplished are the results mentioned above

    and this problem has been for over a year

  4. #4
    so considered the altitude should I be using more or less pop off valve pressure

  5. #5

    Join Date
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    Is the power valve motor working properly? I've seen a bad motor hold one at lower rpms and then come on all at once. Took some playing with the throttle to be able to even get it to try to go. As soon as the throttle was released I had to wait for it to come back open again. Just a possibility.

  6. #6
    Less maybe? I'm not a carb expert though. But the fact that there is "less" air at 5000ft and your still running lean means there is a serious problem. If you were to run that at sea level you would be in severe danger of a lean siezure.

  7. #7

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    Popoff should be no longer the prime suspect at that throttle percentage...Not sure what carb (s) are on a 760....but they are usually about all the same setup...Google "Mikinui sbn manual" page 17, says main jet handle most of the fuel in that range...but anything that could limit fuel is a player....filiters, pump, fuel selector, needle not coming off the seat far enough or restriction any where in fuel supply.....high speed screw is add some to over come it, but it is still lean....do not run until going in and looking for the problem...and remember, all circuits below that throttle position are still adding thier percentage of fuel and do not shut off, if they are lean the total will be lean.
    Last edited by Crazypirate; 04-04-2017 at 06:37 AM.

  8. #8

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    Mikuni SBN PDF.... http://www.mikuni.com/pdf/sbn_manual.pdf

    page 13, 1/3 to 3/4 throttle is the main jet. I'd also be looking for a fuel blockage though, the small filters in the carbs on the pump side, or internal passageways

  9. #9
    ok so carbs have been rebuild ed with the sbt rebuild kit could get the mikuni kits here in Mexico so new filters selector valve is free flow no problem there main fuel filter is ok too i will check the main and pilot jets to see if they are according to manual and also check for bent arm on the pop off


    can the sbt kit be the problem?????

  10. #10
    So today I checked the main jets and they are according to Yamaha manual so the only thing I have left to check or change are all the fuel lines thinking one could have a little Crack and could be getting air some where or again can the sbt pump diafragm is too stiff?? What else would you check

    Again thanks for your help

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