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Help FZR250 3LN3 carb problem.

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

  1. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    You say you've checked the spark - checked each plug for carbon buildup?

    Ignition timing isn't adjustable on these things
     
  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Not sure if i've mentioned it before but have you checked the hole's at the bottom of the mixture screw thread's in the base of the carby's are open, and you can see through them into the main bore of the carby?
    Mine was running a bit intermittant on number one carb, so i pulled the mixture screw out and found a small slither of rubber that would sometime's block the tiny port
    If these port's are blocked then you won't get it to idle, especially without choke
    Also have you tried raising the idle speed a little bit ?

    [​IMG]
     
  3. Gert

    Gert Well-Known Member Premium Member

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    Have you checked with a timing light if there is an spark with starting?

    If you have fuel there, and there is an spark, she should run. Except there is no compression. But I can hardly believe that there is no compression on each cilinder.
     
  4. G1D1

    G1D1 Member

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    @ruckusman yep I’ve had the spark plugs out several times, and they have been replaced in this process. Spark is strong in them, I found a loose connection to the coil pack which I suspect was the intermittent loss of power and sluggishness that would appear and disappear (similar to your problem no??).

    @my67xr good call, I will check these holes. The o-ring in each of these was difficult to get out, it was pretty much stuck in there and needed scraping out, each one came out in tiny little pieces so I will check to see if I missed any little bits. Good advice, thanks. Do you think it wouldn’t be starting if the mixture screws aren’t set correctly? So far I’ve tried 1.75 turns out and 3 turns out, nothing in between. It runs with a little bit of fuel down each carb so not sure why it isn’t starting!!

    @Gert haven’t tried a timing light, but that would be next step today. Not 100% sure on how to do this? Any advice would be grand. Thanks!
     
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  5. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    It would be nice to have found and solved an electrical cause for the occasional misbehaviour.

    Hopefully @my67xr has solved the not starting issue with the potential of blocked jets
     
  6. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    This is the complete pilot circuit ... all those passageways and holes need checking for that reason

    remove the bung carefully

    https://litetek.co/Guide_MikuniPilotMergeChamber.html


    Pilot Merge Chamber.png
     
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  7. G1D1

    G1D1 Member

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    Thanks @GreyImport, got it running!

    My process so far was:
    1) change pilot merge chamber bung o-ring; put back together and no change
    2) new spark plugs, tested and running but very poorly
    3) rebuild carbs with keyster kits, cleaned and sprayed compressed air through. Note: did not re-remove bungs for this. I fear this was my fatal error.
    4) put back together and still not running; diagnosed fuel delivery system and checked spark, bike running from dropping fuel down each carb. Noticed connector to coil very loose and corroded, leads me to think initial problem was this coil pack intermittently dropping in and out, leading to sluggishness that would appear and disappear at random.
    5) stripped carbs INCLUDING bung to pilot merge chamber, sprayed with compressed air and re-assembled. @my67xr i checked mixture screw and realised first time round I had assembled cylinder 4 with o-ring and washer on the wrong way, which wouldn’t have been helping.
    6) re-assembled and started first try. Needs some tinkering with mixture screws to iron out flat spots on rev range, and also might need to adjust exup valve to get smooth revs from 6-10,000 rpm. Now just putting new plugs and terminals on connection to coil pack, and time to do some test runs!

    Thanks for your help @GreyImport, @ruckusman and @my67xr, wouldn’t have been able to do it without you
     
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  8. ruckusman

    ruckusman White Mans Magic Master Premium Member Dirty Wheel Club

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    Great work - it gets tricky and frustrating when there's more than one issue in play as the symptoms can be contradictory
     
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  9. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  10. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Correct me if I am wrong, but once you removed the bungs and blew out the pilot circuit it was good?
     
  11. G1D1

    G1D1 Member

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    Correct, however also swapped over the o-ring and washer on cyl 4 mixture screw. They were in the incorrect order.

    I have diagnosed the original problem I was having with sluggish intermittent throttle to a bad connection between the coil pack, but cleaning out the pilot circuit seems to be what allowed it to start.
     
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  12. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Speaking of the pilot merge bung. I made a tool with a flat on it. Fit into the bung and just jiggle lightly side to side and it comes out easily. You cannot rotate the bung because it has a flat on the outside as well.
    PilotMergeBungTool.jpg
     
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  13. Gert

    Gert Well-Known Member Premium Member

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    Well now, five years later and since the Keyster kit, (cold)startup is not what I hoped.
    Because I think that can be better, I ordered the emulsion tubes from Yamaha, the needles are not available anymore.

    When I rebuilded the carbs five years ago, I forgot to clean the bungs. So I do that now. The were pretty easy to achieve, but I don't have new seals.
    I asked Blair for help and he told me he has them. I asked if he would ship them and how much he wants, but since then, it is silent. Dunno why? Perhaps, from Holland Blair is impossible to reach?

    So, I installed the bungs with the old seals and put the carbs on the bike. Further nothing changed this time.
    The bike started good, but will not rev past ± 6.000 rpm.

    With my new original tubes I installed the old Yamaha needles. Perhaps those were to worn too?
    So, I swappeld the needles with the Keyster ones, but that does not help.

    Added my A/F meter and I see that she is way too lean. Hmm, since I adjusted fuel level with the new Keyster tubes, I problably have to do that again with the new Yamaha tubes.
    Or I can reïnstall the Keyster tubes and leave everything in place. Actually, warm she ran fine with the Keyster stuff.

    I have to sleep a night over it and see what I will do.
     
  14. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Gert I sent you an email telling you that I can send them but I received no reply.
    Just sent you a private message.
    Cheers
    Blair
     
    Last edited: Jan 27, 2021
  15. Gert

    Gert Well-Known Member Premium Member

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    I know, I replied multiple times, but never got response. I will sent now one again.
     
  16. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Okay got it and replied.
     
  17. Gert

    Gert Well-Known Member Premium Member

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    Decided to install the Keyster tubes again and see what happens. Now she revs freely, so I can be sure that the Keyster tubes differ from the Yamaha ones.
    Changing the needles did not make much difference.
    Downside, one cilinder quit working. Problably due to messing around with all this tubes and needles.

    Now I wait for the seals Blair is going to sent me and then I am giving all carbs an complete cleanup and rebuild them with the Yamaha tubes and (old) Yamaha needles. That means I have to adjust fuel level again, but hey, why not.
     
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  18. Cj Ryder

    Cj Ryder Member

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    This does seem out of place although I managed to brush all the numbers of my carbs when I rebuilt them and took’em for a deep cleanse outside and in


    Sent from my iPhone using Tapatalk
     
  19. driftwood

    driftwood Member

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    @my67xr , do you know of a cross-section diag anywhere? I can't see thru the pilot screw hole on any carbs, let alone the one that's giving me the shiites. This one keeps weeping fuel down, which doesn't seem to be coming from the emulsion tube - more like the hole adjacent butterfly.
     

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  20. driftwood

    driftwood Member

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    Dohhhh, pls disregard my last.... 3 are clear. One won't open up - can't get a 0.3mm carb wire in, for any. Anyone know what size the pilot hole in the throat is?
     

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