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  1. #1

    Join Date
    Jul 2006
    Location
    West Bend, WI
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    Carb tuning questions - need to fix bogging

    Background:
    '99 GP1200 w/ 130 hours, bought used last summer - first ever boat for me
    Modded over the winter with:
    ADA billet head w/ 42cc domes
    Pre-mix conversion (running a bit leaner than 40:1 with Pennsoil synthetic always use either 91 or 93 octane gas)
    K&N Flame arrestors
    Solas XO prop
    R&D Rideplate
    Worx intake grate

    Had some engine trouble early this year - turns out someone was in the engine prior to me buying the boat and doing the above bolt ons, long and short I melted two pistons so since then we've done:

    SBT cylindar swap
    1/2 over pistons
    Carb rebuild
    New needles & jets
    Primer conversion

    I got it back from the shop, all tuned up and ready to go. However, it bogged after starting until the engine got quite warm. It was fine from idle (which seemed fast to me) up to about 4000 RPM and then it would bog and either die if I stayed on throttle or sit back down at idle if I let off. Once it got past this, however, it ran fantastic, best it's been, which I would expect after all this work and I hit 66MPH on the stock speedo in rough chop. But the bogging was really annoying and would do it during 360 turns, intermittently during riding at low RPMs and after sitting for even 5 minutes or so even after 1/2 hour of riding.

    So I start playing with the low speed screws and idle. I turned up the idle which got rid of the bogging after startup, but now it bogs after running for a while and getting good and warmed up. When trying to do 360's etc. or jumping waves, if the RPM get to low it bogs and I've got to wait for the idle to settle back down. In addition now I can only hit 61MPH on the stock speedo. I did some searching here and @ Riva yesterday and decided to start all over. I screwed in the low speed until lightly seated, turned them back out 1 1/4 and set the idle so that it was about 1350/1400 (using only the tach on the stock multigauge). I rode around for over an hour yesterday turning, tweaking, and every time I thought I had it set it would prove not to be. When I've got it set to run right from a standstill (i.e. no bogging at 4k RPMs) it'll bog at low throttle when it gets warmed up. When I adjust the idle when warm so there is no bogging at low speeds then from startup it bogs.

    I'm at my wits end. This is my first experience with tuning a carb and I've learned everything from posts here. I'm hoping someone can lead me down the right path.


  2. #2
    Moderator RX951's Avatar
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    Welcome to the Forum Byteme

  3. #3
    RAIDER RUNNER BULLRAIDER's Avatar
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    Byte,.... did you adjust your popoff for the flame arrestors, did you remove your chokes??what is your pop-off at now???

  4. #4

    Join Date
    Jul 2006
    Location
    West Bend, WI
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    Quote Originally Posted by BULLRAIDER
    Byte,.... did you adjust your popoff for the flame arrestors, did you remove your chokes??what is your pop-off at now???
    Popoff? The chokes were removed when installing the primer, I saw the choke plates and everything they took out. The shop did it when they rebuilt the top end and carbs.

    I'm enough of a newb with carbs that I don't know what or where to adjust popoff. I've got the service manual on PDF but can't find it in there either.

  5. #5
    mile_hi_1300's Avatar
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    Denver
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    Hey Byteme,
    there are some members who have put together some stellar info over the years about just about every aspect of maintenance and performance for this sport. Fernando put this doc together and Hydrotoys hosts it on his site. This doc goes through pop-off pressure testing toward the end. I hope it'll help.
    http://www.hydrotoys.com/gpr/tuners/...orAssembly.pdf

  6. #6
    My understanding is that the issue has more to do with throttle position and not the RPM's you are pulling. Someone on this site was kind enough to shoot me a copy of the SBN manual and it covers some basic tuning. It sounds to me like you are lean on your pop off. The pop off can be adjusted through a combination of the needles and springs. Shoot me a pm with you email address and I'll send you the manual.

  7. #7

    Join Date
    Jul 2006
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    West Bend, WI
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    Thanks!

    I just talked to the guy that rebuilt it and he didn't change anything or check popoff after the rebuild of the carbs.

    He did tell me that he used:

    115 gram springs
    1.5 needle and seat
    90 pilot jet and
    135 main jet.

    I'm gonna see if I can get this thing tuned to pull good low and mid using the idle and low speed adjustment and then work the high end using the high speed adjuster.

  8. #8
    RAIDER RUNNER BULLRAIDER's Avatar
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    Byte ,you need to set your pop off lower, ,since you installed flame arrestors and also removed the chokes . You can start with 95 gram springs, and try them , but you may end up with the 80 gram, leave the 1.5 n/s in there.this really will make a world of difference.

  9. #9
    Dave Sharp dav_dman's Avatar
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    holy schnitzge's, 90 low jets will kill you with f/a's when you let off throttle after cruising at 3/4 throttle. I predict you'll lock up tighter than a drum within 20 hours of use.

    As soon as you hit the bog, pump the primer a really quick a couple times.. if it takes off with a new life then you know you're lean. It could be popoff, like bull is saying, but my popoff was good with 1.5's and 115 springs and f/a's so i don't think so. Under full throttle, both jets come into play, and you are about 10pts low and your highs might not be adjusted in since this guy thinks 90 is good for your setup. Pull em, man.

    Put 100's on the lows and set your high screws fat at 1 turn out. If that doesn't do it then drop back to 95 springs like Bull suggested. Just my thoughts...

  10. #10

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    West Bend, WI
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    OK, thanks guys. Glad I posted the numbers.

    I'm going to order 100 pilots jets and the 95 gram springs all at once just in case. WTF, they're only $2 each.

    How hard is this to do myself? I really don't want to pull the ski and take it in, but I do want it done right. I've never done anything on a carb but turn the low speed screws and idle adjustment...

    That being said I do know what I'm doing with a wrench, just never put one to a carb before.

    Anything else I should do when I'm in there?

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