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Project GSX250 restoration

Discussion in 'Your 250cc Projects' started by SwarleyAUS, Mar 21, 2017.

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  1. SwarleyAUS

    SwarleyAUS Well-Known Member

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    OK so pressing on the mixture screw didn't seem to do anything.

    https://www.facebook.com/video.php?v=10212777717296524


    Suspecting an air leak... Think it's on the intake side. All clamps are tight as I can do them up by hand but the airbox ports were always a really loose fit on the carb intakes. I had already put duct tape on the carby intakes themselves to try to seal this connection a bit better, don't think it's worked though.

    After applying the WD40, eventually the idle came down to a nice 1500-odd rpm =D

    https://www.facebook.com/video.php?v=10212777701896139


    So just gotta seal up those boots.

    Next issue to rectify is that applying throttle causes the engine to cut out o_O
     
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    SwarleyAUS, Apr 1, 2017
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  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    How many turn's out are the mixture screw's now ?
     
    my67xr, Apr 1, 2017
    #62
  3. SwarleyAUS

    SwarleyAUS Well-Known Member

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    1 turn throughout both those videos. Should probably put them back to 1.5 turns, that's what the manual suggests
     
    Last edited: Apr 1, 2017
    SwarleyAUS, Apr 1, 2017
    #63
  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    When it started and was first running in the video above, were you holding the throttle at all ?
    If not then i would be removing the fuel bowl's and checking the jet's are all clean, and the emulsion tube's
    Part number's #21, #23 and #25 in the service manual
    To remove part #23 will require the top's of the carby's to be removed as well as the slide's (part #9 up to part number #1 in the service manual)

    The pilot jet's (part number #21 in service manual) sound like they might be blocked, check the hole through the middle isn't blocked or partly blocked and check all the hole's across the jet are open
     
    my67xr, Apr 1, 2017
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  5. SwarleyAUS

    SwarleyAUS Well-Known Member

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    No, no throttle. Everytime it has been running any throttle causes the bike to stall. Ok I will look to do that unless this information clarifies anything:

    Put the mixture screws back to 1.5 turns and with the choke out (on) the bike idles at ~5k rpm. As I adjust the choke, the idle speed changes to the point that with the choke completely off the bike stalls. With about 1/3 choke the bike sits happily at 1500 rpm though.

    Thanks for your help!
     
    SwarleyAUS, Apr 1, 2017
    #65
  6. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    If you are needing choke to keep it running, then you definately have an air leak.
     
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    Murdo, Apr 1, 2017
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  7. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Ok, glad we've got it diagnosed! Is the fact that applying throttle causes the engine to stall tied to the jets possibly being blocked? I'm not an expert but I don't see the throttle issue being due to air leaks. Throttle should feed in more petrol no?
     
    SwarleyAUS, Apr 1, 2017
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  8. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Throttle controls the butterflies in the carbs, which allow more air in. Venturi (vacuum ) effect then draws in fuel at a faster rate. If your jets/venturii are blocked, the bike will stall as the mixture becomes too lean to burn.

    With CV carbs, having the airbox and it being sealed is critical. Without the airbox at all, you'll get an extremely lean mixture, think about 18:1 where normal/good is 12-13:1 and stoichiometric aka "perfect" mixture is 14.7:1. Too lean and you will start to damage or melt the pistons/ringlands or suffer exhaust valve failure via extreme temperatures.
     
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    Linkin, Apr 1, 2017
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  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Yeah blocked jet's in the carby guessing it might be more in your pilot jet though.
    When you open the throttle it start's letting more air in which draws fuel in
    The pilot jet is the one responsible for fuel from idle up to and around 3/4 throttle.
    The needle let's fuel in from around 1/4 throttle and up, then 3/4 to full throttle is the main jet, the pilot and needle also help at full throttle

    Ideally you need to pull the carby's apart and give them a thorough clean out
    Maybe even a full carby rebuild kit from Keyster if they are available for your bike
     
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    my67xr, Apr 1, 2017
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  10. Johnny

    Johnny Well-Known Member Premium Member

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    Read this: http://www.cycleorings.com/intake.html
    Those o-rings sold on that site wouldn't fit a 250, I think, not sure though, but I wouldn't bet on that. But all the information about them and what they cause when they go bad applies for sure. So read that. I changed the intake boots and o-rings on mine, I ordered parts from Partzilla.
     
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    Johnny, Apr 1, 2017
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  11. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Ok I'll clean the jets tomorrow. Originally opened the carbs to check function and clean out old petrol. Didn't clean the jets tho as I felt I wouldn't be able to get it all back together again right! Fuel was yellow but not thick so I had hoped nothing would be blocked.

    My cylinder intake boots are solid rubber as far as I'm aware. If not I'll have leant something new tomorrow! All the rubber bits are very hard, managed to soften the carb intake funnels a bit, so I wouldn't put it past the carb-boot seal being bad.
     
    SwarleyAUS, Apr 1, 2017
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  12. SwarleyAUS

    SwarleyAUS Well-Known Member

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    One other minor question, the boots that are in the airbox, the ones that funnel air into the carb... the ones on my bike no longer fit over the carb intake opening. I assume they are meant to but have shrunk over time?
     
    SwarleyAUS, Apr 1, 2017
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  13. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    You could try heating up the carby/airbox boot's with a hair dryer, or in boiling water then quickly fit them to the carby and do up the clamp
    Could try some Dielectric grease on the boot's too, that can help to soften them up
    Supercheap etc sell a small tube of it for $11 - http://www.supercheapauto.com.au/Product/Permatex-Dielectric-Grease-33-oz/379868

    Otherwise search for some new old stock boot's,
    i was lucky enough to find a set of new old stock airbox boot's for my FZR at a decent price on ebay
     
    my67xr, Apr 1, 2017
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  14. SwarleyAUS

    SwarleyAUS Well-Known Member

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    I managed to soften them up in brake fluid, but they didn't recover - if they ever were meant to fit over the carb. Yet to find a diagram of these funnels on the web that match my bike's. I might try heating them and stretching if we diagnose the leak to be with the carb intake, cheers.
     
    SwarleyAUS, Apr 1, 2017
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  15. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    my67xr, Apr 2, 2017
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  16. Johnny

    Johnny Well-Known Member Premium Member

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    Inside of the intake boots are O-rings which start to leak first, the boot itself may still be fine. Not saying that you definitely have that problem. But at the moment, if you haven't gotten the airbox fastened to the carbs then that's where the air leak currently is! :D
     
    Johnny, Apr 2, 2017
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  17. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Yeah they're like the GS250. So are they supposed to sit over the carb intake nozzles or just butt up against them?

    Johnny when you're talking about intake boots you mean engine-carb boots still yes? I'll take a look today. Air box and engine boots all have hose clamps done up as tight as I can do them. Engine-carb boots are plastic-hard currently though.

    What I'll do today to diagnose the leak is play with the choke to get a lower idle and then spray wd40. As I said with the choke only 1/3 on the idle speed is about right at 1500rpm, so I'll start there. I didn't realise the wd40 is meant to increase the idle speed. I was looking to see the idle come down with the wd40, which it did for whatever reason, but I should be looking for the idle to go up when I apply it I now understand.
     
    SwarleyAUS, Apr 2, 2017
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  18. Johnny

    Johnny Well-Known Member Premium Member

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    Yes, the intake boots are between carbies and cylinders, and those boots have an O-ring under them that starts leaking air after some time. But the connection between an airbox and carbs is as important. And the airfilter, never run your bike without an airfilter.
     
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    Johnny, Apr 2, 2017
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  19. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    @SwarleyAUS if the idle speed change's in any way there is an airleak

    The airbox boot's slip over the flange on the carby then you tighten the clamp
    Look's like they are still available new part number # 13881 44100
    I have used the Sikaflex urethane to glue my carby/airbox boot's into my FZR airbox before i found new boot's, it worked well as a temporary fix
    My boot's had shrunk at the airbox end

    20160620_122313.jpg


    If i were you i'd pull the fuel bowl's off and at least take the Pilot jet's out and clean then up with some Threebond Super Engine Conditioner ($14 at Repco), poke a strand of fishing line through all the hole's a few time's to push out any dried fuel/gum
    May as well clean the Main jet's at the same time, the jet's are simple to remove and refit

    tbond.jpg
     
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    my67xr, Apr 2, 2017
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  20. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    You need to clean the carbs totally .... anything less and u will chase your tail forever .... take pics before u pull something apart/off ... lay everything out in neat order .... theres plenty of threads on carb cleaning ... and yes the ultimate tool is the can of Threebond

    Be thankful u only have 2 carbs to do

    I suggest u become a Premium Member and have a look at the manual and the parts diagrams of the carbs

    https://www.2fiftycc.com/index.php?resources/categories/gs250-gsx250.34/

    https://www.2fiftycc.com/index.php?account/upgrades


    Table.jpg
     
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    GreyImport, Apr 2, 2017
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