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  1. #1

    98 GP1200 just rebuilt carbs but bogs @ low speed

    Just rebuilt all 3 carbs and set the low/high speed screws to the recommended turns in the post here on SBT forum. Replaced all the filters too. pop-off pressures great.

    Took it out today for the first time since rebuild... starts up great and idles wonderful ... but at WOT from idle and coming off high speed run -> will start to bog down and has audible noise that sounds like it is pushing alot through the carbs.. (not sure how to describe the noise since it isn't really missing or hesitating) - just sounds like it can't process the mixture and will slow down ... then at a higher RPM (forgot to look).. hold on and runs fantastic.

    Not sure if I should adjust the low speed or high speed adjusters since I don't want to mess with that higher RPM power..

    Any help would be appreciated.

    Thanks.


  2. #2
    Yamaha artisan Cutlass's Avatar
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    Any mods to the GP or is it 100% factory stock?
    when you idle around a bit the exhaust starts to fill up water from the cooling system. When you go WOT, it takes a little bit for the engine's exhaust to clear out the water and then it'll take off. Is that what you're experiencing?

  3. #3

    Carbs

    It is stock. No mods of any kind. I don't believe there is water filling up in the exhaust as the sound doesn't change from the starting idle. That sounds good. Also, after it runs good at WOT and I slow down to turn right, left, or not quite back down to full idle ---going back to WOT it happens again. My gut feeling is that it is in the carbs...

    What were you thinking about the exhaust?

    Thanks for your help...

  4. #4
    A child of five would understand this. Go get one. pierowman's Avatar
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    What he is talking about with the exhaust is specific to idling and then hitting WOT. The cooling water pools up in the exhaust and the engine has to blow this out before it runs properly. Search Jetworks mod.

    I have the same feeling that you are having a carb issue. Did you make sure you didnt have any air leaks in the carb? around the needle seat or the pump side? Change the fuel filter in the carbs. Just thoughts.

  5. #5
    Yamaha artisan Cutlass's Avatar
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    Agreed, doesn't sound like the water clearing out of the exhaust because it also happens after you slow down from WOT. Only extended idles cause water to pool in the exhaust. What caused you to rebuild the carbs? Were you having a problem before?

  6. #6
    I rebuilt the carbs because I bought the ski at the end of the season last year and took it our once. It had a low end hesitation, but not the same bog as it has now. I did not know the status of the carbs, so they I rebuilt them. I don't believe there is a leak anywhere.. the pop off test went well at the needle and seat. I changed the internal filters in all three carbs at the same time. I set the low speed adjusters to the specs in the SBT sticky... 1 1/4 front and center, 1 1/8 +/- 1/4 for the rear. The high speed adjusters were set to 1/2 front and rear, 7/8 +/- 1/4 for the center. I read elswhere in this forum a different setting.. Think is was Oside post... Could that be the problem?

    I live about 1.5 hours from the lake so testing is a pain... plus removal of the flame arrestor to get to the adjusters to turn just a bit is lengthy..

    I do appreciate your input guys.. looks like it will be a fun summer.

  7. #7
    Yamaha artisan Cutlass's Avatar
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    You have the stock settings correct, which should work well on a stock machine. Are you using geniune Mikuni kits or aftermarket kits? Have you read the Mikuni SBN carb manual? that might help you potentially pinpoint what carb circuit is giving you issues. From your description, it almost sounds like a pop-off issue(the regulator part of the carb:needle and seats, spring arms and springs.)
    Other then a possible carb issue, have you checked the compression and spark plug condition?

  8. #8
    I used the kits from SBT for the rebuild. Compression is great and equal in all three cylinders. New plugs.. Not sure what the Mikuni manual is but if there is info that lets me separate the three carbs, that might very useful. Can you point me in the direction where to find this? Thanks alot for your help.

  9. #9
    Yamaha artisan Cutlass's Avatar
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    Sorry. I meant to post the link but I forget to. Here it is:

    http://www.mikuni.com/pdf/sbn_manual.pdf

  10. #10
    Yamaha artisan Cutlass's Avatar
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    BTW, part of your problem could be the SBT carb kits. Some people have bad luck with them. The genuine Mikuni kits are the only thing I'd use.

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