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Help Bandit 250 problem.

Discussion in 'Suzuki 250cc In-line 4's' started by Alibongobingo, Mar 18, 2018.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    When this, or what was describes as, 'chugging' was being investigated in the past, @ruckusman would turn his fuel tap off and the problem would go away then he would have to turn the tap back on. As I recall.
     
  2. ruckusman

    ruckusman Well-Known Member Premium Member Dirty Wheel Club

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    This is a well worn path for the Fizzer owners amongst us - I think some of us would be guilty of having tried to blame the phase of the moon for the intermittent irregular behaviour...I know I howled at it frequently enough

    It's the needles and emulsion tubes
     
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  3. ruckusman

    ruckusman Well-Known Member Premium Member Dirty Wheel Club

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    https://www.aliexpress.com/item/1-s...t-Configuration-Jet-needle-J/32787900867.html

    @maelstrom has recalled correctly - I commuted on the Fizzer 5 days a week, riding it 7 days a week for over 12 months, doing in excess of 20,000 kms on the thing
    Turning the fuel tap off would slowly deplete the fuel in the carbs, eventually leaning it off enough to get going - that seemingly insignificant oval wear on the emulsion tube would allow significant amounts of extra fuel to enter the air stream when the engine was idling or close to idle speed - figuring out why this would seemingly happen at random is something best left to quantum physicists.

    Litetek seal kits are also highly recommended
     
  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    This is a badly worn needle (FZR1000)

    worn12.gif
    And this is a worn emulsion tube (left)
    The centre hole will be slightly oval shaped if worn or worse

    emulsion_tube_end.jpg
     
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  5. Alibongobingo

    Alibongobingo Member

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    Yes. I've discovered that shutting the fuel off seems to make it come back quicker
     
  6. Alibongobingo

    Alibongobingo Member

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    My Bike:
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    So I get new emulsion tubes?

    Really appreciate all the help guys.

    Meanwhile..out of interest.. My ZZR600 developed sympathy pains. Ha (I'm probably not allowed to talk about non 250's here.) It was flooding at the lights and bogging.
    Anyway. That was easy to sort. The spring in the float valve of cylinder 1 was stuck in, thus effectively raising the float height on cylinder 1 to unacceptable levels. Easy issue to find and fix.

    So i can fix bikes. Lol.
    I just wish this little Bandit would be so forthcoming with its issues.

    Al.
     
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  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Well a visual inspection of the needles and emulsion tubes would be the first step.
     
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  8. ruckusman

    ruckusman Well-Known Member Premium Member Dirty Wheel Club

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    My original mistake was a visual inspection which didn't see the minuscule amount of wear which is sufficient to cause problems
     
  9. Alibongobingo

    Alibongobingo Member

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    Bearing in mind I have stripped, cleaned and rebuilt these carbies twice and didn't see any obvious wear.
    But then i wasn't looking for miniscule wear so......

    Lets take em off and apart again.
     
  10. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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  11. ruckusman

    ruckusman Well-Known Member Premium Member Dirty Wheel Club

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    @maelstrom had a chart with needle diameters - the clearance between the two is tiny at the idle position

    the various emulsion tube (needle jet) diameters and the relevant - notice the steps are in 0.005 millimetre increments

    I believe the bandit 250 is O-1 - 2.605mm - now if you can find the needle diameter you subtract one from the other to get the clearance for the thickest part of the needle - it's a really tiny amount...

    202004d1299590703-tm-38-press-needle-jets-needle-jet-size-chart.jpg
     
  12. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    You don't want to know how many time's my tank and carby's have been off, and played with then tuned etc.


    Going by the spec's listed below the needle's are 2.5mm at the widest point, so the needle when sitting inside the emulsion tube has .0525mm clearance all round

    You can buy the needle and emulsion tube's seperately too,
    Suzuki Bandit 250,
    5CF9-3 needle and O-1 emulsion tube $13 per pair inc delivery
    But that jet plate gasket is something that can leak, so you are probably better off buying the full kit

    https://www.aliexpress.com/item/1-s...id=b33aa023-4efd-42e7-b51d-026546c07620&tpp=1
     
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    Last edited: Mar 30, 2018
  13. Alibongobingo

    Alibongobingo Member

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    Stripped and dismantled again.
    Thise needles are near perfect, shiney. Tubes look good, even under a magnifying glass. This does not mean they are good i suppose.

    I'm still thinking what difference it makes when setting off and i keep getting back to if it's not electrical (so load) , then it is the floats being forced backwards by inertia. (Yes I know, the bike is going forwards and the fliats want to stay where they are, it's all relative)
    Anyway, given that pinching the fuel line seems to be how to get it out of chug mode I deduce that it must be lowering the fuel level in the carbs that cures it.

    So one last attempt before new parts are purchased..

    I'm going to set the float levels a bit lower than they 'should' be.

    This will probably make no difference or make it worse.

    It's a good job ive nothing better to do this easter break.

    Watch this space.
     
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  14. Wozza

    Wozza Active Member

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    Long shot...but if you have a set of micro scales (digital kitchen scales may work)weigh the floats..I had a hell of a time with my Bro inlaws 4 barrel holly carb on his ford monster truck flooding on the front. We replaced just about every component bar the float..yep it was much heavier than the rear one...we did the bubble test and shake test but missed the fact it was heavier....
     
  15. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    With all the different models of Bandit it might be tricky to find the correct float height for your model.
     
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  16. Alibongobingo

    Alibongobingo Member

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    Floats set 'too' low. (Or lower than i looked up they 'should' be. Just a puffteenth of a bee's dick.

    No chug mode :) 3 laps of the block including several set offs and hill starts and no chug. Fingers crossed .

    I feel a bit stupid if it was the float height, but glad I've fixed it, even if it's really just masking something else.
    I really hope it stays good.

    Now...let's get those pilot screws right before we move on to a sync.. I'm at 1.25 turns and getting a slight reluctance at WOT, smooth through to the redline at slightly less than WOT,
    Revs in nuetral hang slightly when dropping to idle. Idle somewhat up and down, can't get it too steady (warmed engine) will fluctuate between 700 and 1500 rpm.

    So happy it's not chugging. :)

    Thanks guys..
    20180331_165003.jpg
     
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  17. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Haha, float level are important.


    The service manual for the GJ74A say's the mixture screw's should start at 1 turn out,
    then warm up the bike and tune from there
    Does it feel flat at wot, or is it spluttering, flat is too lean (turn mixture screw out 1/4 turn and try again), spluttering is too rich (turn mixture screw in 1/4 turn)
    There is no float height listed in the service manual for the GJ74A 45hp model, just the 40hp model

    Surging idle sound's like a vacuum leak, have you tried spraying the intake manifold's with degreaser or wd40 with the bike idling, if the idle speed changes in any way there's a leak there.
    It could also be carb sync
     
  18. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I found a couple of Japanese blog's saying the float height should be 14.6mm off the fuel bowl mounting face
    Sound close to what you have ?
     
  19. Alibongobingo

    Alibongobingo Member

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    Vacuum leak was my first thought on that surging idle. I'll test tomorrow.

    Yes, flat at WOT. So I'll try a little richer. -After I sort any vacuum leaks or I'll be doing it again if i set to incorrect air.

    Incidentally. I've not much to compare to as all my smaller bikes have been singles or twins. The smallest 4 cylinder bike I've ever had is a 600. I have had two 250's. A CBR250 (single) and a GPX (twin).

    This bandit hasn't much bottom end power. I'm assuming it's supposed to be like that but it needs 4k+ on the taco to accelerate me up a hill. I'm finding I'm gearing down more to keep it on the boil.

    But then it is a dinky engine and i am 100kg so perhaps I'm just asking too much.
    I just remember my gpx feeling more sprightly. Perhaps not.

    Anyway I'm not fixing it to ride myself as I'm physically too big for the frame.

    I'll say this though. The little bugger is a hoot! Knee down on the little suburban roundabouts. It weighs nothing. I'd have to be going much, much faster on my ZZR600 to have a smile like that.
     
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  20. Alibongobingo

    Alibongobingo Member

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    I'm about 1mm above that now.
     

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