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Discussion FZR250 3LN1 or 3LN3/5 Keyster kits

Discussion in 'Yamaha 250cc In-Line 4's' started by ruckusman, Nov 26, 2021.

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Hey Guys,

    Is anyone intending to purchase, or already has purchased one of these kits for their carbs?

    I would like to measure the emulsion tubes.

    If anyone is intending to purchase some - give me a holler

    This is why - the Chinese kits I bought, whilst usable for my purpose, they would suffer from accelerated needle/emulsion tube wear, and I'd like to know if the keyster kits are what they are supposed to be with respect to the emulsion tubes

    https://www.2fiftycc.com/index.php?threads/alternative-carburettors-fzr250-3ln1.11370/#post-144493
     
  2. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    I wasn't terribly impressed with the keyster orings, cant comment on the other bits as the engine died well before it should have :(
     
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  3. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Fortunately I had the o-ring and seal kit from Litetek @maelstrom - but that was well before we even knew about the keyster kits and had misdiagnosed the running problems as 5 or more things entirely - that was a real learning curve...

    Out of interest, what happened to the engine?
    Only tell that story if it won't re-traumatise you all over again
     
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  4. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    Probably should have mentioned it was a CBR250RR, not an FZR. It overheated in traffic due to a binned fan switch and I didn't realize it until way too late (someone behind me honked, I looked back and saw steam pouring out the exhaust). It managed to get me the 90 miles back home at near it's top speed with only one short break, which I'm certain is what did the most damage to it.
     
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  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I assume that warped the head or something as equally bad
     
  6. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    Bearings are screwed up, and one of the cylinders is also in bad shape. I haven't checked the head yet because I bought a different engine that wasn't restricted so I can have 45HPs ;)
     
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  7. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    It's almost a happy accident then
     
  8. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    If only the unrestricted engines upper case half wasn't damaged in shipping!
     
  9. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    OH JAYZUS, and of course the lower and upper halves are matched pairs - repairable?

    Out of interest, what are the differences, engine wise between the unrestricted -v- restricted?
     
  10. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    Matched set yes. Might have Millenium Technologies weld it up and see if I can't have them match the pistons to the cylinders. DPO is a "mechanic" and apparentely doesn't know things like those are matched on size. Head came in a bunch of pieces with all of the buckets and shims tossed in a bag so none of that is matched up either! At least he didn't pull the valves out I guess.

    from memory unrestricted/restricted differences in the engine are only
    intake port size
    exhaust port size
    Crank trigger wheel
    I think the cams may be slightly different as well.

    outside of the engine...
    carb adapter
    jetting
    header size
    ECU
    Wiring harness
    switch blocks
     
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  11. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    That's a very informative list, thank you

    So Honda change [presumably reduced] port sizes - I think I've checked valve sizes and they are unchanged as are stem diameters from MC17 onwards

    Altered static timing, [possibly retarded it slightly via the crank trigger wheel]
    Cams like the FZR250 3LN1/3/5 -> 3LN6/7 and zeal I suspect lower lift and possibly different lobe centres and possibly duration - TBD

    I'm failry certain that I have seen mention of getting MC19 cams for higher peak power

    That header size change is interesting, if it reduces and does reduce power

    ECU - less maximum advance

    I did just come across mention that the carb adapters are different between earlier and later model MC22's on the xcite bikes website - now I want to know the differences

    It's basically a list of potential small improvements, it seems that the OEM's settled on 45PS and then all had slightly different recipes for attaining that
     
  12. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    If you really want to know the differences between models grab a copy of `CBR 250 Maintenance Guide.doc` from here https://www.facebook.com/groups/2056978107961182/files (CBR250RR AUS group files section) While it says "maintenance guide" it is a gold mine of technical specs.

    ID/OD of the intake boots are only 1mm larger on the unrestricted as checked with my al cheapo calipers, I don't have a good way to measure the exhaust port but the ID is the same between them. I spotted the difference when I met up with an MC19 a few years back (idiot sold that bike for pennies on the dollar because he didn't know how to list it on craigslist, I would have scooped that sucker up in a heartbeat!)

    Valves themselves are identical between the models.

    MC19 is the sweet cam to have by the numbers.
     
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  13. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    I've just applied to join that group - thanks

    When you say ID OD of the intake boots, I've got a rock hard set here, goes from carb throat diameter of ~30.5mm down 26mm at the other end in a fairly steep taper - these are off of VP20a carbs - is that restricted or unrestricted?
     
  14. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  15. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    restricted: 29mm
    unrestricted 30mm
    measured at the narrowest part of the port
     
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  16. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Awesome, and that specifications document is great thanks @GreyImport - I know that is a page on the forum, but it's great to have a document

    Seem I have the unrestricted carbs and carb boots - WHOOT WHOOH

    Now I just have to make them fit...;) - it's doable
     
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  17. thebeefsalad

    thebeefsalad Well-Known Member Premium Member

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    Carbs are identical between restricted/unrestricted, only jetting differs.
     
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