Almost Done Just need to Tune Carbs
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Almost Done Just need to Tune Carbs

This is a discussion on Almost Done Just need to Tune Carbs within the Technical forums, part of the Caferacer.net Forums category; Any body have any good Carb Tuning guides availabe? I've got a GS425 79 that is done except for tuning the carbs. It has pod ...

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  1. #1
    Senior Member BrianH's Avatar
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    Almost Done Just need to Tune Carbs

    Any body have any good Carb Tuning guides availabe?

    I've got a GS425 79 that is done except for tuning the carbs.

    It has pod filters and a two to two exhaust.

    Everyone says start with the main jet first, then work your way down.

    Stock it had a 110 main so I'm thinking of running a 115? Does that sound like a good place to start?

    I had it running real rich and pulling hard through all the gears, but unfortunately the richness fouled up the plugs too badly and the bike lost power and started stuttering.

    Anyways this is the final segment of the build and i'm getting de-motivated trying to get these Carbs right.


    Any help is appreciated.


  2. #2
    Senior Member sdurand76's Avatar
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    don't have a carb guide to post, but the bigger the number on the jet - the bigger the whole. if you're running rich going up a jet size will make it worse

  3. #3
    Senior Member BrianH's Avatar
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    Yeah I understand that. I guess I should specify I was running a 117.5 wile running rich. Not the stock 110 jet.

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  5. #4
    Senior Member BrianH's Avatar
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    Anybody? Basic Cab Tuning Theory?

  6. #5
    Senior Member crazypj's Avatar
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    You have Mikuni CV carbs, there's gazillions of information on them.
    look for 4 cyl with about double you engine size.(early GS/GSX, Z1000, some Yamaha's)
    Don't bother looking at Honda, they use Kei-Hin
    Start searching and let us know what you find

    PJ
    I dabble in rocket science, when I\'m not picking my nose
    The other night I gave my girlfriend an orgasm, but, she spat it back at me

    'you can take my word for it or argue until you find out I'm right'

  7. #6
    Senior Member BrianH's Avatar
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    hanks PJ. Just wanted to know if anyone had some guidelines on how to go about tuning the carbs properly after changing the intake flow on a bike.

    My guess is starts with the mains, I was going to run two sizes up from the stock 110, which would put me at 115's.

    Run it at open throttle see how the plugs look and how the bike feels.

    If thats proper i would then go onto the needle jet and play with the height settings until I got the midrange correct with no stutter and smooth acceleration.

    One thing I am concerned about is the transition between different jets.

    Then last move onto the pilot make sure idle is stable, play with the mixture screws etc.

    This is the first time I've re-jetted carbs let alone rebuilt a bike this and after posting on the gsresources(a great site for the suzuki gs line), posting here, and searching through a lot of information what I explained above sounds like the general idea.

    I'm sure there is a lot more to it than that, but ill keeping looking for more info.




  8. #7
    Senior Member BrianH's Avatar
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    Heres a pretty good article for CV carb tuning if anyone else is interested.
    http://www.factorypro.com/tech_tunin...m_engines.html

  9. #8
    Senior Member BrianH's Avatar
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    Little up date on the tuneage.

    Like instructed i first decided to tackle the main jet. The stock jet in the bike was a 110, so I upped it to a 115 to compensate for the pod filters added on the bike.

    On a cold run the bike ran well on full throttle top end. After the bike warmed up a bit, it had some stuttering and dead spots in the top end full throttle range.

    I'm thinking that the pilot is too large, because according to that CV carb tuning link i posted, i rich problem will get worse as the engine warms up.

    One other thing to note is that the low end and mid range after the bike is warm is extremely stuttery, its not like the engines missing or anything, its almost as if the fuel is being turned on and off, thats how drastic the stutters are.




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