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  1. #1

    GP1200 - Bad Reeds??

    Okay, I have rebuilt the carbs with Mikuni parts, put in new 1.5 N/S, kept main jet 135 and pilot 110, new 115 gram spring. Pop offs all at 50 across the board, doubled check valves, low and high speed adjusted per Mikuni specs, new plugs, primer installed.. just installed for premix and loaded up fuel tank at 40:1.

    Ski starts up great in driveway, but low speed rev is rough.. like it is missing, and WOT will climb slower than expected then hit the top. With quick throttle bursts, I see air/fuel mixture come flying back at me when looking down carbs. Forum search indicates bad reeds will cause this..

    My question: will the bad reeds cause the other symptoms (missing and rev problems) as well? Originally rebuilt carbs due to low end hesitation under load at the lake.

    Also, since it looks like I need to replace the reeds, do you all recommend reed stuffers at the same time? I have read a little bit about these on teh forums.

    Ski is a 1998 GP1200. Thanks in advance for your help.

    B. Holt


  2. #2
    Yamaha artisan Cutlass's Avatar
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    110 jet is a little big for a stock GP1200, but it does kinda sound like the reeds might not be sealing well. But reeds aren't a 100% perfect seal. I expect some spray back would be normal.
    Yes reed stuffers are a good mod.
    Stock air box or aftermarket flame arrestors? I'm trying to figure out if your popoff is appropriate for your setup.
    Either way, you should be running the ski with airbox/arrestor on as running without it affects the signal the carbs get and can cause running issues.

  3. #3
    Cutlass... made a mistake in my original post... 100 pilot jets... It is a stock air box with stock flame arrestors.. 50 psi is what has been recommended to me in other posts.. The spray back when reving is pretty significant I would say. Made me pull my face back the first time when it hit me.. Even with the stock air box and FA installed, it still runs the same way..

    I am not really interested in modding this ski if I don't have to.. Just want it to run well on weekends for this summer.

    As far as the popoff reading, have you ever seen a table for appropriate pop-off pressure, especially for stock carbs? That would be great.. I just can't find one.. Help me out if you would on this.. if the popoff pressure is lower, it will be richer, right? Can't tell right now if it is too rich or too lean... There is a bunch of gas going down the venturis though..

    Anyways, thanks for your help.. (again) LOL.

  4. #4
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    Okay, pulled the carbs (again) and the intake. The reeds look great. They all appear to be sealing well and there are none that are broken or stuck. This is the first time I have dealt with reeds in a 2 stroke, but nothing really seems out of order here.. Please look at the pics and let me know what ya think. They all look just like the first pic.

    Now that brings me back to why it appears there is significant spray back through the carbs with a heavy throttle. Is this normal for a 2 stroke? What other reasons could there be for this?

    I am at a standstill as to why it is missing and running bad with increasing revs through the range. The only thing I haven't gotten into is the CDI, but there seems to be adequate spark to each plug..

    Any thoughts please?? Thanks.

  5. #5
    Yamaha artisan Cutlass's Avatar
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    Reeds look fine to me. So maybe its a fuel/carb issue or a weak spark issue. You'll need an adjustable gap spark tester to really stress test the ignition system. There is also a few tests in the service manual for testing the stator.

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    110 is too high.
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    100s are suggested across all 3. I don't know how that relates to your problem though.

  7. #7

    still running bad.

    Quote Originally Posted by akjose View Post
    110 is too high.
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    100s are suggested across all 3. I don't know how that relates to your problem though.
    I mentioned it above to Cutlass. That was a typo.. They all 3 are 100 pilot.. Thanks for the chart. Still not sure why it is running like poop.

  8. #8
    Moderator OsideBill's Avatar
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    Check Crank Phase this can cause issues like you are decribing. The reeds do not look bad enough for the problem you desrcribe. I would dissassemble the reeds clean them and reinstall. but if you are getting severe blow back check crank phase.

    to check phase bring #1 to TDC and measure from the spark plug hole to top of piston. then check #3 it should be close to an exact match on height.

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    Quote Originally Posted by OsideBill View Post
    Check Crank Phase this can cause issues like you are decribing. The reeds do not look bad enough for the problem you desrcribe. I would dissassemble the reeds clean them and reinstall. but if you are getting severe blow back check crank phase.

    to check phase bring #1 to TDC and measure from the spark plug hole to top of piston. then check #3 it should be close to an exact match on height.
    Bill, what do u do if they don't match? Just wondering for my own knowledge.

  10. #10
    Yamaha artisan Cutlass's Avatar
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    You fix or replace the crankshaft

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