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Help XS 250 air filters

Discussion in 'Yamaha 250cc Twins' started by EBB, May 8, 2020.

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  1. EBB

    EBB Member

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    Hi guy's,
    Been fiddling around today,
    No gaskets on the inlet manifolds,
    There weren't any.
    Made some myself and coated both sides with grease. Far from ideal but good enough for the moment till some arrive.
    No difference.
    Won't start without choke (even when hot)
    Rev's @ 2k then boom, goes up to 4.5K and stays there.
    Stuck my finger in the back of the carb, slides are down !
    Where do I go next, choke, main jets?
    Took it all apart and cleaned it yesterday.
    No change.
    Regarding the vacuum pipes, they blow rather than suck. I feed the carbs via a funnel and blocked the pipe off. Doesn't make any difference on or off.
    Help !!!!!
     
    EBB, May 13, 2020
    #21
  2. EBB

    EBB Member

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    I've sprayed WD40 on the manifolds, no joy.
    So just to recap.
    Bike garaged.
    Timing set
    Open carbs
    Vacuum pipe plugged.
    Runs on choke only
    Rev's shoot up to 4K
    Throttle idle un screwed.
    Air mix screws 3 turns out.
    Thanks
    EBB
     
    EBB, May 13, 2020
    #22
  3. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    I assume you mean that without the choke it will jump up to 4000 rpm.
    Are the throttle butterflies synched?
     
    Last edited: May 13, 2020
    maelstrom, May 13, 2020
    #23
  4. Mike Green

    Mike Green Well-Known Member Premium Member

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    I used open CV carbs on an old CB360 bike I raced for a while. No stacks, no filters, and they were near perfect. Bike was out to 470cc, big cam etc. I've also used GSX750 CV carbs on a Z1, with pods, and again near perfect. There are pod filters and then there are pod filters. You get what you pay for. On this side of the world I highly recommend MikuniOZ. This page has pods and trumpets:

    https://www.mikunioz.com/product-category/air-cleaners-velocity-stacks/?v=8e3eb2c69a18.


    they also do a good range of flanges and manifolds and nearly everything else you could want.
     
    Mike Green, May 13, 2020
    #24
  5. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Were these 2x bike's running standard jetting ?
     
    my67xr, May 13, 2020
    #25
  6. Mike Green

    Mike Green Well-Known Member Premium Member

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    The carbs on the CB360 were off a KZ450 cruiser and jetted & modified. The GSX carbs on the Z1 were fitted and the bike ridden away without a single change
     
    Mike Green, May 13, 2020
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  7. EBB

    EBB Member

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    The butterflies appear to be in sync.
    I'm gonna re check the timing today.
    I don't know a lot about CV carbs
    But I know how carbs work in general.
    I'm not gonna go down the main jet road cos they don't come into play till 3/4 throttle.
    I take it the choke is a fairly simple affair, on or off so I don't think it's that either.
    Confused .com
     
    EBB, May 13, 2020
    #27
  8. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Could be a blockage in the pilot circuit somewhere ?
     
    • Agree Agree x 1
    my67xr, May 13, 2020
    #28
  9. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    upload_2020-5-13_20-42-5.png
     
    GreyImport, May 13, 2020
    #29
  10. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    I think the Chief (Greyimport) has highlighted what I was going to suggest... try going to 2 turns out (Air/fuel mix) and see what that does. if it's better, then go to 1 turn out and see what that does. If it only starts (and runs) with Choke, then idle circuit could be blocked as my67xr suggested.
     
    Frankster, May 13, 2020
    #30
  11. EBB

    EBB Member

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    Hi everyone
    Thanks for all the advice.
    Cleaned the carbs again, blew everything out.
    When I refitted them I thought
    " those carbs are being held in place by a very worn clamp"
    With no air box on all the weight
    Was on the inlet manifolds.
    Bottom line some new clamps and Bingo, the rev's go up and down.
     
    • Nice Work Nice Work x 1
    EBB, May 14, 2020
    #31
  12. EBB

    EBB Member

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    now I've got that sorted
    ( with everyone's help I hasten to add)
    I've now got a platform to work from.
    So, back to the filters,
    Original air box just ain't gonna happen ( not in the UK anyway)
    So can anyone recommend something that isn't gonna get fouled by the frame?
    This bike will never go touring, racing or try to set world records but a couple of 100 miles world be nice.
    Thanks all
    EBB
     
    EBB, May 14, 2020
    #32
  13. Xs250se

    Xs250se Active Member

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    Be aware the xs250se uses a verly different airbox to the other models and is very hard to find now especially the connecting pipes to the carbs. I am changing to clip on airfilters following the original box leaking through age. I have done so without jetting on the past and had no problems with running the 250 engines but im not a high revver myself so tend to cruise fairly sedately.

    Sent from my SM-G935F using Tapatalk
     
    Xs250se, May 14, 2020
    #33
  14. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    If you have to ditch the airbox, then a foam filter is your best bet (I think). It won't restrict the air flow like a pod filter and it will protect your engine from swallowing something it shouldn't.

    Foam filter.JPG
     
    Frankster, May 14, 2020
    #34
  15. Andych

    Andych Moderator Staff Member Premium Member Contributing Member Dirty Wheel Club

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    Andych, May 14, 2020
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  16. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    And make sure the filter's are oiled before trying it out too
     
    my67xr, May 14, 2020
    #36
  17. EBB

    EBB Member

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    Screenshot_20200514_110052_com.android.chrome.jpg any good.?

    These any good.??
     
    EBB, May 14, 2020
    #37
  18. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I heard of a couple of FZR owner's that bought these RamAir filter's,tried them out and found they needed dyno time and rejetting, so both of them sold the filter's on
    RamAir won't give you any advise on jetting/tuning for them either
     
    my67xr, May 14, 2020
    #38
  19. EBB

    EBB Member

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    OK guys,
    Just ordered those Ram Air filters,
    To be honest there isn't a lot out there, just lots of the same thing and I don't want to go down the road of getting something made.
    Anyway, got a friend to read the #'s on the main jet : 145 !
    I suspect this is Way to big.
    Your views please.
    EBB
     
    EBB, May 15, 2020
    #39
  20. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    As I posted above , stock main jet is #117.5 and if it was me thats what I would start with
     
    • Agree Agree x 2
    GreyImport, May 16, 2020
    #40
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