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Thread: Carb help - Suzuki GN250 sputtering and dying at idle

  1. #16
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    28th February 2011 - 17:50
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    Love the look of it ..,... I am still in progress of doing mine ... hell fun to ride
    Seriously thinking of cutting the ass outa mine like yours has had done
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  2. #17
    Join Date
    10th August 2013 - 06:43
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    1984 Suzuki GN250
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    Boulder, CO; USA
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    15
    Quote Originally Posted by fridayflash View Post
    sounds like youve had a thorough go at it...whats the diaphragm like? anyway good luck with the new carb, gn's are fucken ace bikes man! your one looks cool, was it imported into usa you reckon?
    It has a USA Vin tag on it, but all the auzuki dealers in my area have no idea say that only the GN400 shows up in their databases.
    Its also rare that these came with drum brakes in the front (mine kind of sucks, need to rework them but no point till I get the bike running).

    The diaphragm looks good - it actually looks like it might be new (rubber is soft, no holes, seals well). I think I am going to try to rebuild this one once I get it running with the new one (if that does end up working).

    What is so good about flat-side carbs BTW? Is it just a style thing, or would I get any other benefit out of it?


    Quote Originally Posted by nzmikey View Post
    Love the look of it ..,... I am still in progress of doing mine ... hell fun to ride
    Seriously thinking of cutting the ass outa mine like yours has had done
    Thanks for the compliments on the bike - its far from complete unfortunately. I honestly couldnt decide what i wanted out of it, but I really dig the look of the japanese style brat bikes. So I just went for it and didnt look back. Now, I kind of want to weld up some extensions so I can fab up a nicer seat. The angle of the one I have on it now makes it slightly un-ergonomic to ride, because you are basically trying not to fall off

    Its kind of depenedent on what kind of style your after, but cafe style always looks sexy in white - I would leave them, or chop them a touch and throw a cafe-style rear section = seat (or flat tracker style, also really cool).

    Front forks are a touch too high for me, so I am going to put on some longer rear shocks to bring the seat up a little bit and try to use spacers to level out the tank a little more. I want to turn it into a brat/cafe/streetfighter style because I cant make up my mind
    I stripped the paint off, but ended up leaving it because it looks pretty cool - think I might leave it that way.

    Took a lot of inspiration from this GN400;
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  3. #18
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    9th October 2008 - 15:52
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    The carb your running will always prefer a stock airbox and the top diaphragm is controlling the slide lift based on pressure.
    A flatslide means your accelerator cable will directly pull the carb slide open so will work well with a short V stack and filter.
    Also the gas flow through the flatslide will be approx 20% greater than the cv carb for the same size = a little more power. This is because the flatslide doesn't have the butterfly valve on the airbox side.

    Maybe spend some time looking in the bucket bike threads looking at what works best on their 150cc single cylinder 4 stroke race bikes.
    I have evolved as a KB member.Now nothing I say should be taken seriously.

  4. #19
    Join Date
    10th August 2013 - 06:43
    Bike
    1984 Suzuki GN250
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    Boulder, CO; USA
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    UPDATE:

    So I replaced the carb, and there was absolutely no change. I then ruled out the fuel system as a problem, and once I did that I realized that the battery was NOT charging at idle. I hooked up an old voltmeter I have and found that the voltage was right at 12.8-13, and only crept up to 13.5 at the extreme top end. When the voltage dips towards 12.5 it starts running rough, and at 12.0v it runs like shit and wants to stall and die.


    So now I need to figure out weather its the rectifier or the stator that is the source of the problem. It is getting great spark, and starts right up when its cold, and the battery is fairly new as well so I can rule all those out as well.

    The rectifier gets pretty damn hot after just 2 or 3 minutes of idling so I suspect that it is causing the voltage fluctuations and lack of charging - but is there any way to confirm? I am buying a proper multimeter today so I can test resistance and more precise voltage, but I am 99% sure there are no real shorts anywhere.

    The rectifier is about $100 brand new which is a little steep (Rick's rectifiers, good quality part). So I want to be sure before I purchase it and probably pay for overnight shipping. A stator is $150 too, which is fucked because of how little I paid for the bike

    So, my questions are:

    1. How do I differentiate a bad rectifier with a bad stator?? Any tests that I can do?

    2. And Is it OK to use RTV Sealant (the ultra duty stuff) in place of a gasket around the stator cover? I want to inspect it, but dont want to order another gasket unless I have to (another $30 bucks)

    3. Lastly - what other models use the same motor? I know that the gz250 does - but those are even more uncommon in the US than the GN. I just want to be able to shop around and not have to pay extreme prices. Wondering if the DR250, RM250, etc use the same rectifier and stator.

    At least I think I narrowed down the problem

  5. #20
    Join Date
    17th April 2009 - 14:06
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    the DR250 is supposed to be the same as the GN250, don't know if you have them in the states though
    "I know your about to do something apocalyptically evil but hey, still want to hang"

  6. #21
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    21st June 2014 - 01:57
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    sorry to dig up an old thread, but did you find the problem?? I've been having almost exact same symptoms on my wifes GN250 and tried pretty much everything you tried

  7. #22
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    9th October 2011 - 22:24
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    1987 Suzuki GN250
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    Quote Originally Posted by Zerker View Post
    the DR250 is supposed to be the same as the GN250, don't know if you have them in the states though
    The Volty is identical, GN125/GN400/GZ250 are very similar.
    "If you think you can do it, or think you can't do it, you're right." - Henry T Ford

  8. #23
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    9th October 2011 - 22:24
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    1987 Suzuki GN250
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    Quote Originally Posted by jezpatrol View Post
    sorry to dig up an old thread, but did you find the problem?? I've been having almost exact same symptoms on my wifes GN250 and tried pretty much everything you tried
    I've been having similar symptoms on my GN too. Iain reckons carb may need a clean, but thinks (and I agree with) that starter motor is the cause as it has started to click - he has checked the relay, battery and alternator.
    "If you think you can do it, or think you can't do it, you're right." - Henry T Ford

  9. #24
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    17th April 2011 - 14:39
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    Quote Originally Posted by GDOBSSOR View Post
    The Volty is identical, GN125/GN400/GZ250 are very similar.
    GN 125 only has 2 valves, 250 has 4.
    For a man is a slave to whatever has mastered him. Keep an open mind, just dont let your brains fall out.

  10. #25
    Join Date
    18th February 2017 - 04:03
    Bike
    1989 Suzuki GN 250
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    UK
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    it looks like one of them things

    mine started with same problem today, its completely stock no mods since 1989 lol
    kept it covered through very cold and wet december and january, but started it once every couple of weeks, warmed it up and let it idle for a bit then recovered, anyway went for a ride this morning decided it wont tick over and cuts out every time i stop, unless i keep it at 2 1/2 to 3 thousand revs.
    looking at the thread though i think first port of call is fully optimizing the battery on a drip charge, see if anything changes before stripping it down. could be the cold has goosed the battery, pretty usual here in the UK then after that empty tank and put some fresh petrol in, sometimes it loses octane when stored for a bit, process of elimination - always start with the cheap/free fixes first there's nowt worse than buying a whole load of expensive bits to find out you just had a screw loose, or a badly earthed wire lol trust me I've been there

  11. #26
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    28th January 2015 - 16:17
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    Checking generator system: get yourself a half-decent multimeter, you'll need it.

    Rectifier: check the power diodes, as per this page: http://www.electrosport.com/technica...ting-guide.pdf

    Stator: check the windings for continuity, it shouldn't be more than a few ohms.

    Plugs and wires have to be in good condition, an intermittent contact will send spikes to your reg-rec and kill it in short order.

  12. #27
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    12th April 2006 - 18:44
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    Clean the carb, set adjustments and it should be ok. Fuel coming from tank? Sometimes the tap can clog up.

    If not fuel related, consider electrical. New plug. Check HT lead / replace it. Coil earth. Just undo everything, clean the contacts, and try to run it again. Check coil with an ohmmeter.
    "May all your traffic lights be green and none of your curves have oncoming semis in them." Rocky, American Biker.
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