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Project My '90 FZR250 3LN3

Discussion in 'Your 250cc Projects' started by my67xr, Jun 19, 2016.

  1. my67xr

    my67xr Well-Known Member Premium Member

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    I have been looking at the carby's tonight trying to solve this flat spot.
    I've dropped the float's back down to 16.2mm,
    the only thing is they only move maybe 1mm at the most from the closed position to the open position
    When i blow though the fuel inlet into the needle and seat you can hear it's restricted.

    Another problem, @ruckusman mentioned the Keyster needle's had different spring's in them, yes i can now confirm this.
    With the float tab clip's removed from the needle's, if i push the Keyster needle pin against the genuine needle pin, the genuine needles' pin compress's all the way in before the Keyster pin start's to move.
    The Keyster needle must have a spring with twice the tension as the original one
    So that would mean that the Keyster one will shut off the fuel flow earlier than the original needle, possibly giving it a lower float level

     

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  2. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Very interesting. In a static situation the fuel should shut off as soon as the Viton coated tip seats, which would negate the spring difference, but under running conditions we can expect something else.
    I am thinking that the spring acts like a shock absorber. If we imagine the extreme case, no spring, the needle would tend to bounce off the seat as the fuel sloshes around in the bowl and the bike moves as a result of bumps etc, so it implies that the spring would help to keep the valve closed under those conditions. Therefore the stronger spring will behave more like the former and be more likely to flood than the OEM part.

    I love the video @my67xr, can't argue against that evidence.
     
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    Last edited: Oct 4, 2017
  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Taking it to the next step, the more pressure against the float the stronger the required spring. If the float only has a small arc of possible movement before seating then you would expect to use a weaker spring and vice versa. So I could guess that the BDST (downdraft carbs) would have small arcs of movement and weak springs and the BST carbs will have the opposite.
     
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  4. my67xr

    my67xr Well-Known Member Premium Member

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    I've messaged Keyster via their Facebook page (they were showing as online) asking about the spring in the float needle, also asked them about the bigger main jet's in the 2x centre caby's
    Just waiting to hear back from them now.
    https://2fiftycc.com/index.php?threads/fzr250r-3ln3-bdst28-carburetors.9643/

    The adjustment tab on the float would be lucky to move 1mm with the float height set at 16.2mm.

    I had a decent look through the 3LN service manual supplement for the 3LN3 carby spec's, jet's and float height/fuel level etc but can't find mention of it anywhere.
    There is spec's on the 3LN1 carby's, infact they are in 2 place's of the service manual?


    Anyway i have the FZR back together again, carb's etc and have just tuned it and re synced the carby's
    About to put the tank back on and give it a run.


    I made that video showing the float needle spring difference, incase Keyster was also interested.
    A couple of year's ago i was chasing some spring's for one of my bike's, i went to a spring maker and he let me have a look through his old stock.
    I asked how to tell the difference in spring tension when comparing spring, he told me that trick ^, and if you want to compare spring extension rate's, you hook the 2 springs together end on end and pull them apart.
    You can soon see which spring has less tension.
     
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    Last edited: Oct 4, 2017
  5. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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  6. my67xr

    my67xr Well-Known Member Premium Member

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    I have only seen the pdf copy of the genuine service manual supplement that is uploaded here in the resource's area.
    All the jet size's etc are in the part's catalogue, just no float height / fuel level etc
    And being that the 3LN1 carby's are different to the 3LN3 carby's and the jetting is different etc, i wondered if the float level is different too ?
     
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Yes that one was donated by me. It is a Webike copy of the OEM. The paper is rubbish so you are better off buying a second hand OEM one off the Japanese auction sites.
     
  8. beano

    beano Well-Known Member Premium Member

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    I have collated all the info i could find on these carbies into a table below, it seems the only real info missing is the fuel levels on the 3ln-3 on machines.

    Carb Chart.PNG

    Apart from finding someone from Japan that may be able to find out this info (and i have tried messaging owners on twitter, facebook etc to no avail) and even messaged some guys that have owners blogs for example here:

    http://www.pushpushpush.net/archives/2017/03/19161201.php

    So i think purchasing the supplement is going to be the only way to find out, i have no problem throwing a few bucks into the ring if it will benefit the forum, ye guys are what made my rebuild possible so iv'e no problem giving a little back if its required, just a thought anyway...........
     
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  9. my67xr

    my67xr Well-Known Member Premium Member

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    My Bike:
    Yamaha's, FZR250 3LN3 1990, XT250TS 57R 1986, IT200L 43G 1984
    Tried the bike out this arvo, still no good with the 16.2mm float height
    Will have to try it higher again
     
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  10. my67xr

    my67xr Well-Known Member Premium Member

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    My Bike:
    Yamaha's, FZR250 3LN3 1990, XT250TS 57R 1986, IT200L 43G 1984
    I'm trying to work out if my EXUP servo isnt working properly?
    When the key is turned on it cycles as it should, and the flap sits slightly open when the bike is idling.
    When it's revved in neutral, the flap opens a bit.
    With the exup disconnected from the TCI, i get a reading of 0 Ohms with it closed and 2.52K Ohms open so.the potentiometer is working?
    Has anyone else had an EXUP servo fail ?
     
    Last edited: Oct 4, 2017
  11. ruckusman

    ruckusman Well-Known Member Premium Member

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    I'd be looking a frayed cable preventing the EXUP from working properly - I had a cable snap once and it wouldn't rev properly for the last 5Kms home.

    Only detail I can recall is that it open gradually so the performance hit you're suffering sounds symptomatic of something related to the EXUP
     
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  12. my67xr

    my67xr Well-Known Member Premium Member

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    It open's smoothly, the cable's were taken off a year ago and lubed too
    Just seem's to be rich down low, and slow to rev, engine sound is deep when accelerating
     
  13. ruckusman

    ruckusman Well-Known Member Premium Member

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    I always found lean made the exhaust sound deeper, a bit like Tibetan throat singing - like when you forget to turn the fuel tap on and it runs out, not that I've ever done that

    Only thing I can think of is have the air passage holes in the bottom of the slides been drilled? Supposedly this makes them more responsive, but I could see it leaning things off briefly as fuel flow increases to adjust
     
  14. Joker

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

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    I have two spares if you need a replacement.
     
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  15. my67xr

    my67xr Well-Known Member Premium Member

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    My Bike:
    Yamaha's, FZR250 3LN3 1990, XT250TS 57R 1986, IT200L 43G 1984
    Finally had a win today.
    Took fuel bowl's off and raised the float's to 14.7mm
    Found an easy way to bend the float tab's, there's a small hole toward's the float end of the tab.
    I just put a needle into the hole and the tab bend's really easy, easy to keep the tab square to the float too.

    20171007_125800.jpg 20171007_125446.jpg

    Put the float's back in and bowl's on, primed the pump a few time's to fill the bowl's and started it up.
    Engine sounded a lot better, so i let it warm up and adjusted the mixture screw's once it was warm.
    Started at 2.5 turn's out, and ended up at 2 1/4 turn's out, it's responsive and almost crisp sounding now.
    Took it out for a short ride, when i gave it a blip rev going out my driveway i thought it felt a lot better.
    Out on the road it has never gone this good since i've owned it !
    Going out for another longer ride in a little while, just about to refit the fairing's

    I'll give it a better tune some time in the next few day's,
    will get the Carbtune onto it again to sync the carb's, and get the mixture's closer to perfect.
     
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  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    So can you recap?
    • You fitted COP
    • Rebuilt the TCI
    • Changed any carb jets, needles etc?
    • current float height at 14.7mm
     
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  17. my67xr

    my67xr Well-Known Member Premium Member

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    Yeah, it has been a bit drawn out
    Fitted Keyster carby kit's and had the hestation at 3500 - 4000 rpm
    Tried various float level's etc and settled with it at 16mm, with a hesitation.

    Synced carb's with my home made sync tool, adjusted mixture's and got it a bit better, still had a 3500 rpm hesistation

    Replaced the rubber intake's with some better used one's, still cracked but were urethaned and sealed
    Used better Carbtune sync tool and got the carby's synced close to perfect, mixture's closer again, replaced the dirty stock air filter with a K&N custom filter fitted in stack air filter panel housing, still got the hesitation at 3000 rpm

    Fitted coil on plug's, and Irridium spark plug's, engine was running better again
    Tried hooking up more direct power to the coil's bypassing the TCI, buit that caused power feedback problem's (had a relay ticking over a lot when the ignition was turned off.

    Tried a larger pilot jet (changed the #10 to a #12) but had a too rich bottom end issue, it wouldn't rev clean off idle, or rev past 6000 rpm.

    Tried the needle clip on the 2nd position down (Leaner) but didn't help, tried it in the 4 position down (richer) and that didn't help either.
    Ended up fitting the standard #10 pilot jet back in, with needle clip back on the 3rd position down (standard), tried float level's at 14mm, and 13mm with mixture's set to 2 turn's out
    Would rev better of idle, but didn't sound right (deep), and would quickly drop after you let go of the throttle.

    Replaced the capacitor's in the TCI (most were upgraded to a low ESR, higher voltage cap), and also replaced the 2x Darlington transistor's with new oe spec tranny's
    Fitted new replacement rubber intake's, set float level to 14.7mm, mixture screw's to 3 turn's out
    Engine started and idled ok, had a slight hesitation off idle, but after warming up and a bit of tuning, set the mixture screw's back to 2.25 turn's out and hit the sweet spot !

    To get the best float level i started at 16.2mm and went by the throttle response off idle, raised it till it didn't hesitate, then tuned the mixture's to suit

    Probably missed a few more change's, adjustment's above too?

    Still going to give it a more thorough tune when i can make the time using the Carbtune sync tool, digital non contact thermometer and maybe an 02 sensor and gauge if i can rig up a basic wideband sensor in the tail pipe to suss out mixture's at idle, mid and top end.
     
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  18. ruckusman

    ruckusman Well-Known Member Premium Member

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    That's an almost full circle on the carb settings.

    Did you fit all of the keyster components to the carbs, or just the worn emulsion tubes and needles?

    From memory of carb fuel circuit charts that hesitation is on the transition from pilot to needle

    Do you consider that there would possibly be any change in airflow through the new filter.

    I assume that you cut another filter down to fit the aperture in the old filter housing. I'd love to see details of this as I've been considering doing the same thing given that the OEM filters are effectively unobtaniun
     
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  19. my67xr

    my67xr Well-Known Member Premium Member

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    Yeah pretty much fitted the full Keyster kit's, just minus the fuel bowl seal's.
    The modded filter is why i was playing around with the pilot size and needle clip height,
    i thought the modified air filter may have increased the flow, but not too sure now.
    Comparing my modified filter to a K&N panel filter i think mine has more row's of element and not so open as a K&N
    I tried it with no oil, and ended up using spray on filter oil (Castrol) on the element to richen up the mixture's a little, probably closer to the oem filter air flow ?
    There's pic's of the K&N modified filter on this thread, post #260- https://2fiftycc.com/index.php?threads/my-90-fzr250-3ln3.8776/page-13
     
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  20. my67xr

    my67xr Well-Known Member Premium Member

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    A few other thing's i have done to the FZR while i've been trying to work out the carb's

    I bought another fuel tap (used) off ebay japan for $25 inc delivery, and put the new Litetek seal's in in, thank's again to @maelstrom
    Pulled it down and bead blasted it, then fitted new seal's and some 316 socket head cap screw's
    Also fitted the new Litetek seal's to a resprayed lower water pipe housing, (same OR057 seal's as FZR400)




    1 fuel tap.jpg

    2 fuel tap.jpg

    20170914_112625.jpg
    20171007_183610.jpg

    OR-057_Fitment_Small.jpg



    I have modded the rear tail light so it now sit's flush with the surround, and trimmed down the rear number plate panels' bottom lip 25mm, so it now finishes at the number plate and remounted the reflector for a neater look.

    My left foot peg rubber was very worn on the front edge so i took it off and used an angle grinder with a 1mm cutting disc to recut some slot's into it and make it look better as well.
    I found an even better solution to this today though

    20171008_210537.jpg 20171008_210609.jpg
    .
     
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