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Project FZR250 project

Discussion in 'Your 250cc Projects' started by neoncrypnid, Mar 1, 2020.

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  1. beano

    beano Well-Known Member Premium Member

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    Do as stated above, my bike had almost identical issues back in the day.

    First check that the float valve is working then set the fuel level correctly, I'd be extremely surprised if that doesn't fix it assuming that the jets/needles/mix screws haven't been messed with.
     
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    beano, Mar 8, 2020
    #21
  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The backfiring on deceleration is because you have a leaking exhaust. When you back off the exhaust sucks fresh air in which ignites unburnt fuel.
     
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    maelstrom, Mar 9, 2020
    #22
  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    What @beano said. You can download the 2KR workshop manual from the resources section once you pay to be a member.
    The fuel level is listed as 17.5 to 19.5mm on page 86.
     
    maelstrom, Mar 9, 2020
    #23
  4. neoncrypnid

    neoncrypnid Well-Known Member Premium Member

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    I think I found the exhaust leak. The bike has an EXUP exhaust with the valve cut out. When i reassembled it i forgot the metal gasket. Just found it this morning on my bench.

    I'll do the float heights now. Thanks
     
    neoncrypnid, Mar 9, 2020
    #24
  5. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Just in case, the value I gave is fuel level not float height.
     
    maelstrom, Mar 9, 2020
    #25
  6. neoncrypnid

    neoncrypnid Well-Known Member Premium Member

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    Carbs are off the bike, I followed this info for flaot height
    https://litetek.co/Guide_Mikuni_BDST_Fuel_Level.html

    , but either the flaots are set way way out or there not the original design.
    The photos a bit crap cos I was holding it with one hand, but the float is a solid 6mm from the 16mm mark. Done with needle seated, spring uncompressed


    20200309_132509.jpg
     
    neoncrypnid, Mar 9, 2020
    #26
  7. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    The 2KR carbs are different to 3LN, which is what that guide is for. Measure the highest part of the float as pictured and that is your float height. Spec will be in the base FZR250 manual, unsure if we have that in resources.
     
    Linkin, Mar 9, 2020
    #27
  8. neoncrypnid

    neoncrypnid Well-Known Member Premium Member

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    I see, you are right. My carbs are 3LN but there the 3LN6/7 ones. They are not original
     
    neoncrypnid, Mar 9, 2020
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  9. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    maelstrom, Mar 9, 2020
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  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    You have a 3HX1. From what I can see, your frame, engine and carbs are all 3HX1. On this forum we generally call all the pre 3LN series as 2KR.
     
    maelstrom, Mar 9, 2020
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  11. neoncrypnid

    neoncrypnid Well-Known Member Premium Member

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    Sorry, must be mistaken. I thought based on the slides and needle mechanism it was the later model. The needles definitely have the spring mechanism and slides have the notched bottom. I though they were exclusive to the 6/7.


    20200309_144538.jpg

    I measured all floats at 10.5mm give or take 0.5
     
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    neoncrypnid, Mar 9, 2020
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  12. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I have not seen any float heights listed for the 2KR. Someone might have done it like @ruckusman did for the 3LN
     
    maelstrom, Mar 9, 2020
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  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I suggest checking the choke circuit and the sizes of the jets that you said are new. Often people fit the wrong parts, drill jets to make them useless, and fit larger sizes to make their bikes go slower, wear rings out faster and foul plugs.
     
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    maelstrom, Mar 9, 2020
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  14. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Heres your 2KR BDS26

    2kr carb.jpg


    And the 3LN BDST28


    carb 1.jpg
     
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    GreyImport, Mar 9, 2020
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  15. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    That's beautiful work right there, I never realised we had fuel level for the 2KR - it should be simple enough to work out where the measuring point is if it isn't a similar casting line on the float bowl like the 3LN's

    Now remember that the sum of the float height AND the float level came to 25.2 - 25.4mm for the 3LN's - the inch seems to creep in here, so with a fuel level of say 17.5 - that would make the float level of approximately 8mm - IF THE 2KR IS THE SAME

    So you know that your float levels are at about 10 - 10.5mm, DON'T change anything, but now measure the fuel level and see if you can find somewhere that makes sense as a measurement point for a fuel level reading around 17.5 - 19.5mm

    If there's a sensible measuring point which is at about 15mm, I'd say the float levels are about 2mm too high, but don't go bending anything willy nilly - it's a merry-go-round that's almost impossible to get off of, I know, I've been there
     
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    ruckusman, Mar 9, 2020
    #35
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    The manual has an image of measuring the fuel level.
     
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    maelstrom, Mar 9, 2020
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  17. neoncrypnid

    neoncrypnid Well-Known Member Premium Member

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    So to measure the fuel level, I should chuck a bit of clear tubing on the drain and bring it up above the carbs so i can see how high the fuel is? Is this right?
    And just to clarify the carbs are definitely from the 2KR? Even with the different slides and spring on the needle?

    I'll pull them down again and check all the jets, not sure if they are new but they definitely looked it. I'm not sure theres a problem with richness because all the plugs are a nice brown, not black. For clarity, I'm basing fuel consumption on a mid sized dirt bike by the way, it might actually be normal.

    I coudnt find the manual in the resources page you mentioned. Sorry for all the dumb questions, I'm sure you lot talk someone like me through this stuff every few weeks lol
     
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    neoncrypnid, Mar 9, 2020
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  18. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    GreyImport, Mar 9, 2020
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  19. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    It is all there and yes it is always the same questions, but generally speaking we are a happy bunch of campers.
    Yours is a 1HX which uses the same carbs as the 2KR. Some jets and parts may be different as the 1HX runs the EXUP. You will need the supplement for the 1HX if you want to be certain of the exact fuel level for your model.
    2KR_03.jpg
     
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    maelstrom, Mar 9, 2020
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  20. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    We help you out and teach you, then when someone new comes along you'll likely step up and help to teach them and on it goes - we all get wiser around here and everybody is really helpful

    I think everybody owes everybody else a beer here from some time in the past
     
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    ruckusman, Mar 9, 2020
    #40
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