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Help FZR250 3LN3 carb problem.

Discussion in 'Yamaha 250cc In-Line 4's' started by Gert, Jun 15, 2016.

  1. Cj Ryder

    Cj Ryder Member

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    Are the zeal carbs 3ln carbs? Or 3yx-14900-00 confused if that's a single part number or the whole assembly of the mikuni carbs

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  2. Cj Ryder

    Cj Ryder Member

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    That's severe, Did it run prior to removing the piston heads? I stopped attempting cranking the engine when the wrong sparks are inside

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  3. Gert

    Gert Well-Known Member Premium Member

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    I take care too, but under WOT at about 250 km/h it was too late....
     
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  4. Gert

    Gert Well-Known Member Premium Member

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    Installed the carbs, started, warmed up, sprayed some brake cleaner at the bottom of the boot and the engine immediately responded...huh??
    Took a closer look and discovered many tiny little hair cracks.
    So, no ali boots for me, new Yamaha boots are going to be ordered.
     
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  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Yes sometimes u have to really squish them to show the cracks

    carb boots.png
     
  6. Gert

    Gert Well-Known Member Premium Member

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    Man, I must be blind :oops::oops:

    [​IMG]
     
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  7. tryin from China

    tryin from China Active Member Premium Member

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    Not really because the slide has a different housing which will not retrofit to the 3LN1. Sorry.

    But since I have all 3 generations of carburetors, I will make an effort to photograph the differences side by side for compatibility and contrast.
     
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  8. Gert

    Gert Well-Known Member Premium Member

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    Well, bad news. Yamaha Europe does not deliver the carburator joints (anymore?). So I am stick to AliExpress or try to repair the old ones.
    A local guy told me last week, he glued all of his cracks (Suzuki joints) and drove for years without any problems.

    Anyway, I will try some other oversea sellers and see what happens.
     
  9. Gert

    Gert Well-Known Member Premium Member

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    Got message from the Ali that the joints are in my country already. For security I also ordered the cheap Ali joints. Better bad boots than no boots.

    Got mail from Impex (https://en.impex-jp.com/) that they can deliver the oem carburator joints. So I ordered there. Now, let's hope they are really in the position to arrange real oem Yamaha boots and that they don't buy them from China and put them in a Yamaha bag and ship them. Who knows?

    When I ordered some electronic parts for my E34 M5 lately, the dealer provided me an exact copy of the China part I ordered some days earlier. On both parts the BMW logo was missing, except that the dealer had sticked an litte white sticker on the part with "BMW" printed on it..... hmmm suspicious.....
     
  10. Gert

    Gert Well-Known Member Premium Member

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    Well the saga continues.
    The China carb joints did already arrive. Measured them, they fit. Around the carb throat, the rubber is less thick. And the synchronise screw is smaller in diameter.
    Anyway, the joint does seal good top and bottom.
    I think in the issue in an 'running' engine or an 'no running' engine, these China boots are te best bet there is.

    But, ofcourse, the next problem knocked on the door.
    The choke pipe fall off:

    [​IMG]

    Probably my own fault, but that does not help. How do I solve this?
    Must I find me a second hand set of carbs? Or one? Or can this be fixed? Anyone?
     
  11. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    You could flare the brass a tiny bit, reinsert it and then put a tiny amount of epoxy around in a ring over the top, it needs to be spotlessly clean for it to work obviously
     
  12. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Yep just epoxy it back on

    choke pipe.jpg

    Choke pipe 2.JPG
     
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  13. Gert

    Gert Well-Known Member Premium Member

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    Took the carbs to my friend, who does have experience with epoxy. He glued the pipe in place and made some sort of support. Okay with me.
    If this is not going to work, he told me he wil drill the pipes out, add little nipples and connect them with an hose. Whatever, if it works I am happy.
    Checked the pipe for blockage, but it is open, nice.

    [​IMG]


    Received the China carburator joints too. So I layed them down together and made some pics.

    The throat is 2 mm smaller (carb side). Head side is like stock.
    The rubber is pretty flexible, so installing the carbs was not to hard. Dunno how big the throat is from the stock Yamaha joints (if new)?
    My old Yamaha joints are hardened and cracked.

    Left China, right old Yamaha.

    [​IMG]

    China = smaller synch screw. Body Yamaha is all metal, China is first rubber and metal inside.

    [​IMG]

    Throat:

    [​IMG]

    [​IMG]

    Outside:

    [​IMG]

    [​IMG]

    Notch for clamp, Yamaha = much bigger. But installed on the carb, the China boot does seal good with clamp:

    [​IMG]

    [​IMG]

    Anyway, installed the boots on the bike and started her. She runs pretty good. Carb settings all stock now. Exact fuel level, new Mikuni emulsion pipes and old Yamaha needles.

    I synchronised the carbs and sprayed some brakecleaner on the boots. I noticed that idle went a little down. But I do not know if that is due to the seals from the throttle shaft. Anyway, she did not stall like before.

    I know these China joints are not ideal, but at the moment I do not have an other option. As soon as I have time I take her out for a test drive.

    In the mean time I wait for Impex.jp if they are really able to get me some stock Yamaha carburator boots.
     
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  14. Gert

    Gert Well-Known Member Premium Member

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    Well, new problem. It is almost impossible to close the synchronise hole. *sigh*

    [​IMG]

    As you can see, the Chinese boot is having about 1 cm rubber in front of the metal thread. The Yamaha boot is all metal with an long screw, now I know why.
    Removed the screw from boot 1 and put my finger on it and I was surprised how strong the "pulse" was. No wonder that small cracks are effecting A/F that much.
    Anyway, driving around and at the same time keeping the holes closed with my fingers is probably not giving much driving pleasure, so I must find me a way to close the hole decently.

    Strange enough I was able to synchronise the carbs with the nipples provided with the carbtune. But if I install the screws provided with the boots, there is an vacuĆ¼m leak.
    Tried allen screws (and normal screws), with rings, without rings, rubber seals, big and small, but all don't work. If you tighten up, the rubber is distorted and leaks air. If not tightened up, it leaks too.
    The rubber is pretty soft, nice for the throat, but not for the screw. And warmed up, the rubber is getting softer.

    Ofcourse there are ways to close the whole, I am sure, but it would be nice if the carbs can be synchronised in the future.
    Perhaps I order another set from China, they are pretty cheap, and mess around to see if I can find me a decent way.

    In the mean time, still hoping for Impex.jp for oem Yamaha boots.
     
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  15. Gert

    Gert Well-Known Member Premium Member

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    Sealed the ali boots with kit, add a very little to the bottom too, between head and boot, installed and let dry.

    [​IMG]

    Tested yesterday and now there are no leaks anymore. If I spray brake cleaner on the boots, nothing happens. Me happy.
    Eventhough, during a testdrive I noticed there is a tiny lean spot at around 4.000 - 6.000 rpm.
    Tweaked a little with the mixture screw, but that did not help either.
    So, ripped the carbs off the bike again and raised the needles one notch = 0,5 mm.
    Started and she ran fine but no time left to test her on the streets.
    Will do that today or tomorrow.

    Anyway, news is that I received an message from Impex that the oem joints are shipped to Holland. Probably one or two weeks delivery. Let's wait. :)

    In the mean time, if these ali boots do function, I think I let them sit and see if they last one or maybe more years.
    To be continued.
     
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  16. jmw76

    jmw76 Well-Known Member Premium Member

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    Those boots look very similar in design to the ones that Suzuki use on the old GSXRs. They are very dependant on a good seal to the intake face on the cylinder head. I run fabricated metal ones on a little race car I have that then connect via silicone sleeves to the carbs (RS40s). I gave up with O rings and now just seal them to the head face with high quality petrol proof RTV. This works a treat and never leaks. The metal adaptors do not age, warp and shrink like the rubber/plastic ones.
     
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  17. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Dowty washers or washers slightly larger than the screws with an o-ring inserted into centre to seal and large head allen key screws might have been simpler

    But it's good to see that you have new sealed boots so can attend to the carb settings knowing that issue is resolved
     
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  18. Gert

    Gert Well-Known Member Premium Member

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    Can be. I do not have those laying around, and second, the rubber is getting really soft when warmed up. It is easy to move/twist the screw (from the side) making it harder to seal.
     
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  19. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    It may be worth seeking them out, dowty washers appear at places that deal with hydraulics

    Otherwise a slightly than larger than the screw belleville washer which is domed and an o-ring around the screw and into that gap would work also

    Thick molybdenum grease would complete the seal or perhaps RTV silicone beneath the washer into the gap underneath the belleville washer

    Final option would be possibly teflon gas tape around the screw itself

    Anyway food for thought in case anyone encounters the same issue with sealing
     
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  20. Gert

    Gert Well-Known Member Premium Member

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    Well, warmed up en sychronised the carbs on top, with these:
    [​IMG]

    Drove the whole weekend and hand it over to my better half, who is the actually driver of this bike.
    She is very happy now. Bike is running like never before.
    New battery, new fuel filter, new and rebuilded front brakes and excellent cleaned carbs :)
     
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