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  1. #1

    New guy with another GP with a bog after full carb rebuild and mysterious idle hang

    Hey all, looking forward to talkin skis with you guys!

    Okay- first things first to get them out of the way....

    I'm familiar with these carbs. I owned or have owned Yammies for the past few seasons (Raider, WB2, GP12). Each one received the same full carb rebuilds upon me purchasing them. I replaced needles and seats with genuine mikuni carb parts. The rebuild kits are the same as well. I bought this GP this year and bought the brand new needle and seat kits the day it came home. I rebuilt the carbs and replaced the oil lines. I replaced the springs for the N/S with identical ones that were in it. The jets were cleaned as well. The ski is a little bit of a hard starter, as my research has led me to believe that I am not the lone ranger there. This past weekend we ran out for a water test and the ski started a little tough and I was lightly feathering the throttle along with choking and once she hit I got a slight "blorp" noise like a muffled backfire. I did have a ton of oil in the case most likely due to running a little premix along with some fresh high-test along with some oil I fed into the carbs as I was priming the lines. Anyway I idled out of the no wake area which would have lasted about 2-3 minutes and gently took off and it kinda stumbled but I chalked it up to all the excess oil in the system and the plugs may have been a little dirty. After a few minutes I went ahead and let it rip from about 30 and it pulled seamlessly, no issues. Whenever we would attempt to stop and idle for more than a few moments though if you try to take it above 3k it seems to bog badly. It runs out to about 59ish indicated no problem but it almost dies at times as well. After riding it for a couple hours I pulled it out of the water and started it to clear it out and it the r's climbed up to about 6k so I blipped the flipper and it revved up but didn't seem to calm down much so I shut it down, then restarted it and it idled fine but if i would rev it to clear it out it would hang again before settling down. Throttle action appears to be normal. I plan to investigate this further by checking for an air leak and all that but I figured I would see if there is anyone else thats been here before. Searching seems to have a few similar results but still not sure... BTW I have read about the water coming in through the exhaust outlet and all that jazz, I just wasn't sure if that would be a contributing factor. I would think you can stab the flipper and be able to not have it almost die... I really don't wanna yank the dang carbs back off but if I have to I will. Who knows maybe even just run it over to the local shop.


  2. #2
    eb87's Avatar
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    Hello, my experience with the GP1200 is that a motor (not in the water) revving to redline like you describe means a vacuum leak on a cylinder which means it's running lean and 2 strokes don't last long running lean. The back of the motor has 2 large crank seals and if you get a backfire or water ingestion it'll blow the seals out against the shaft coupler. Another issue I know about that causes a bog down is a bad check valve inside the carb. It's a clear disk that is concave (looks flat but it isn't) that sometimes will get creased and and allows fuel to flow the wrong way. Hope you can get it figured out.

  3. #3
    I got the idle hang sorted and am looking into a couple other things. My center carb is leaking fuel by the throttle shaft so I have ordered a shaft and butterfly kit. The bog is only there momentarily now. A restrictor was put into the return line and it has fixed many of the issues. The crank seals were checked and they are good. There is a possibility that the check valves are messed up. Carbs will be coming off one last time to investigate while I replace the shaft and install the primer kit.

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