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Help Carbies (I think) giving me a headache

Discussion in 'Yamaha 250cc In-Line 4's' started by GREAZERSOCKS, Apr 7, 2017.

  1. GREAZERSOCKS

    GREAZERSOCKS Grease Monkey Premium Member Contributing Member

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    My Bike:
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    So, I'm now on to my 3rd engine into my FZR. And still having troubles. It's had this same issue with all 3 engine so I'm assuming it has to be the carbs.

    I've pulled down the carbs twice now and cleaned them all out, soaked the Jets and blew everything out with compressed air then synced the carbs to 3 turns out.

    Has new spark plugs and have swapped on multiple coils, and has new rubber carb mounts.

    It mainly idles ok but can here one cylinder mis-firing every now and then. And when riding, its 90% ok.

    But if I'm only holding the throttle on 1/8-1/4 a turn it breaks down and carries on. Or if I've just accelerated pretty hard up to 100 or so and then back off it does the same thing. Breaks down/misses. As soon as I throttle on it's fine. Sometimes it does the same thing whilst accelerating.

    Im just looking for some guidance please as I'm getting pretty sick of it.

    8cde400391065f2fbefddc9675c0da22.jpg

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  2. Joker

    Joker CLUB250 Staff Member Premium Member Ride and Events Crew Contributing Member

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    Have you rebuilt the carbs with keyster kits... might be time for new needles/emulsion tubes to make everything sweet again...?
     
  3. GREAZERSOCKS

    GREAZERSOCKS Grease Monkey Premium Member Contributing Member

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    Was hoping there might have been another option haha don't really have the funds to spend on it ATM

    But if that's the only option, looks like Il have to start saving

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  4. my67xr

    my67xr Well-Known Member Premium Member

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    Keyster kit's are about $220 for the set.
    When you synced the carby's did you do it with the bike running?

    Have you had a non contact infrared temp sensor on the exhaust's just to compare temp's ?
    You can get them off ebay for about $15
     
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  5. Joker

    Joker CLUB250 Staff Member Premium Member Ride and Events Crew Contributing Member

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    Also, have you tried chopping your spark plug leads back 10mm to ensure the connection is correct? May be a current flow issue. They just screw on/off.

    BTW I have a 3LN carby set of keyster kits (x4) with only a couple seals missing I could do you a deal on if you are interested. I won't get around to rebuilding my carbies for some time (also the bike ran fine with them) and I've also got a 3LN5 set of carbies which look in very good condition so I'm not sure I'll need the kits... at least not for a while.
     
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  6. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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    Yep as Joker mentions trim your leads ... might be your misfire

    https://www.2fiftycc.com/index.php?threads/trim-your-spark-leads.8032/

    Are your HT leads setup correctly?

    https://www.2fiftycc.com/index.php?...eads-spark-plug-configuration-inline-4s.8176/

    Hows the exup?

    https://www.2fiftycc.com/index.php?...-powervalve-information-and-maintenance.1099/

    As mentioned the emulsion tubes are something u cant avoid

    Have u put a full Litetek kit thru them?

    I would also be checking the diaphragms ....
    https://www.2fiftycc.com/index.php?...agm-replacement-fzr-3ln-bdst-carburetor.8851/

    Also the the airbox to carb rubbers are available and not too expensive .... and Im assuming the original airbox is still there as the filters are pretty much unobtainable but they are cloth like and u can wash them in hot soapy water and leave them out to dry.

    Have u bench synced them (carb #2 to 3 ... then 3 to 4 ... then 1 to 2)

    Are the pilot screws set up like this?

    PilotScrewAssy.png

    Is this o ring in place under the 4 caps?

    oring.png
     
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  7. G1D1

    G1D1 Member

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    Hey @GREAZERSOCKS did you ever solve this? Was having a similar issue today.
     
  8. my67xr

    my67xr Well-Known Member Premium Member

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    @G1D1 , I think all his 3LN3's are for sale atm
    https://2fiftycc.com/index.php?threads/fzr-250-track-bike-heaps-of-parts.9619/

    Sound's like the emulsion tube's are out of round (worn), probably needle's too

    Try it with the float's all set to 14.7mm off the fuel bowl mounting face, and mixture screw's at somewhere between 2.25 turn's out and 2.75 turn's out

    And check out my thread as i have finally got mine running the best it ever has
    https://2fiftycc.com/index.php?threads/my-90-fzr250-3ln3.8776/
     
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  9. G1D1

    G1D1 Member

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    Nice one, thanks @my67xr. Is there any good links to how to go about this? Never adjusted carbs before, but keen to give it a go!


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  10. Joker

    Joker CLUB250 Staff Member Premium Member Ride and Events Crew Contributing Member

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    I'd be checking your electrics before playing with the carbies too much, just my 2c. Start with going to a shop and buying new leads.. you can get it by the meter from a roll at some bike shops (call in advance, not all have it). I did that early on and since have only really done minor tinkering with my carbies. The 3LN1 engine I just put in runs really well and I haven't touched the carby internals at all. With that said, my carbies were pretty good to start with.
     
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  11. my67xr

    my67xr Well-Known Member Premium Member

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    This is how i set my float level's, cut out a piece of ice cream container with a 14.7mm high cutaway
    Then bend the adjustment tab to suit

    float.jpg

    20171007_125446.jpg
     
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