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carb balancing adjustment screw gsx250f

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by ben1, Aug 30, 2009.

  1. hi all,

    regarding a previous post i have decided to balance out my carbs.
    looking at the manual the picture is not very clear on where the throttle valve balancing screws are, can any1 lead me in the right direction, i can tell from the pic that they are between carbs 2 & 3 near the idle screw.

    and also with the across do i need to remove anything out of the way to get access to the screws?

  2. anybody??
  3. ok just did a balance and the 1&2 ar pretty much even, but 3&4 are all over the place.

    can some body who knows across please show or tell me how to adjust them.
  4. ** Incorrect Information **
  5. thanks rs101,

    and what do i adjust with?where is the screw?

    and with the fuel tank, are you saying even tho the tank is not in the way i will still need to find a reserve.?
  6. Are not the carbs on these 2Xduals, rather than 4 individuals? If so , you may not be able to sync 1&2 and 3&4.

    The screw sits between the carbies on the mechanism.
  7. yes they are in 2xpairs (dual). so its only the 1 screw which is the idle screw the 1 with the spring on the bottom?

    and how do i sync them if they cant be sync together?
  8. Yes, please disregard my original post


    Go to http://suzukiacross.org/downloads/

    Download the manual and the additional diagrams.

    The exploded carb is Fig 11, the Carb Balancing section is 4-11 in the main manual.


    Okay, Item 20 is your balancing screw. It seems that the butterflies can only be adjusted on a per-bank basis (i.e. 1+2, 3+4 at the same time)

    Further trimming comes from adjusting the pilot screws (Item 37)

    Items 41 and 42 are your vaccuum hoses. Here's a setup from a bloke on perth street bikes, with the same colours used. (The hoses have been cut, I probably wouldn't do that to them though.)


    Keep in mind that if you disconnect a hose and are not measuring from it, you will need to block the end using a similar diameter bolt or a plug, much like above.

    You will also need to be supplying fuel to the motor. Whether that's a cleverly positioned tank or a reservoir/funnel, is up to you. Your fuel intake hose is item 49.

    I only have a two-hose manometer, I would start by connecting my manometer to the nipples that 41 connect to, adjust 20 until there is an even vaccuum. I would then reconnect them.

    Then, inspecting the plugs, I would see if there are any cylinders that are running rich/lean. I would then trim the pilot screws paying special attention to the slightly rich/lean cylinders.

    This is all assuming item 4 is okay, apparantly it is notorious for wearing out. Pop the cover off (item 8), and carefully lift out item 9, if the holders are loose and the needles fall anywhere but back in the jet, it WILL damage them! Also, when replacing the diaphragm, ensure that you don't pinch the diaphragm on the cover. May take a go or two.

    Also, search the internet for information on the needle retaining clip, there's quite a few articles on the internet to check it out.

    EDIT: Such as http://suzukiacross.org/2007/05/30/fix-fallen-throttle-slide-holders/
    Hope it helps, took a little bit of preparation!
  9. wow thanks heaps rs101, thats great... really appreciate it.

    one more question about the fuel tank, why do i need to disconect the hose to the fuel tank when the tank is not in the way, cant i just use my normal tank being that its under the seat and not obstructing my work at all?
  10. Sorry, I forget that the across has that removable half-tank boot on it :bolt:
    No problem, just leave it on! More the point was to leave the fuel connected. (Not many other bikes have that luxury)
  11. kool,

    regarding pilot screws, they all need to be turned equally yeh?
  12. No, there's plenty of guys on here who actually have gone about swapping out needles and jets, I've never gone down this path, so they may have a better idea.

    However, I find what works for me is I start and warm the engine, leave it at a fast idle (1500 or so), and then gradually unscrew one screw (making the bike run richer).

    If you hear the engine revs rise, and then fall again, your sweet spot for that cylinder is just after the engine revs stop rising. If as you unscrew the pilot jet, the engine revs fall/gets rougher, you will need to screw it back in (it's running too rich), and again, set the peak point slightly on the lean side of the curve.

    But first I'd probably check out those valve slides!

    (Also, try not to take more then a few minutes while idling at operating temperature. The bike can take longer, but you don't want to have it running all day!)
  13. sorry rs101,

    so you are saying that i turn 1 screw till i hear it rise and then just as i here it fall again that is my sweet spot? and then do another screw and listen for the same etc...? and during the process of turning the 4 screws they can be all turnt to differant settings i.e screw 1 = 1 1/4 turns, screw 2 = 2 turns etc...?

    i have balanced the vacumm hose number #41 in the diagram you posted
    and that was dead even, i used the balance screw #21.

    but the vacumm hose #42 one sided was pulling harder not crazy hard but harder, so i played with the pilot screws and it didnt seem to change the pulling of 1 side, but i did turn all the screws equally 1 1/2 turns each.

    i to only have a 2 hosed sync tool, oo and the throttle slides seem to be in good nic
  14. Might have to put out an appeal for other Across owners, as I have never had to work with a dual butterfly set-up.

    For your questions, yes, they are all going to be about a similar setting, but not necessarily exact.

    And you've pretty much got it, what you're hearing is the engine revs rising due to more fuel being drawn into the motor, then when the mixture gets too rich, the revs start to drop again.

    The screw you're adjusting (item 37) is doing the same job as item 5.

    Once it's all set, you'll also need to rebalance both banks. by the way is looks, you're not going to be able to do much about the variation, you'll probably have to adjust it to a comprimise.

    Also for theory,


    A very thorough explaination to help make it clearer. Have a few beers and possibly even google a few other sites, everyone has a different way of explaining it.
    With this site, however, instead of an "Air Screw", you have a "Pilot Screw" - the same thing, just on the other side of the cycle - fuel, not air.

    And how is the bike running? any specific complaints?
  15. ok no worries,

    thanks heaps for all your help, it was great.

    and the bike is running better, has more pull from take off which is great.

    the only complaint is that it doesnt warm up right.

    before i balanced and moved pilot screws (although pilot screws are in the same position) the bike use to take about 5mins of rev at 3000rpm to warm up, then i could realease and it would just idle.
    but know doesnt seem to matter how long i warm it up it will idle for a minute then conk out, i need to give the throttle a bleep to boost it back up, but then same thing happens.

    but once i have ridden it and warmed it up more than just sitting it is fine.
  16. wind out the idle mixture screws half a turn
  17. To make it richer?
  18. Bingo!

    Turn however far you need to and still remain in that "sweet spot" on the fuelling curve. If 1/2 turn might be too much, then try 1/4 of a turn first to see how you go.

    And don't forget to rebalance!
  19. ok i started from scratch and ended up turning the pilot screws 2 1/4 turns they are all roughley the same, rebalanced the carbs they are as even as i could make them (actually they are pretty much spot on).

    just took the bike for a spin around the block, and i must say it feels totally differant (in a good way) it is so smooth and idles beautifully.

    so just wanted to say thanks to rs101 & iblast for there help, but a very big thankyou to rs101 your help was great, so thanks.

  20. No problem! Glad to help.