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Help FZR rough idle

Discussion in 'Yamaha 250cc In-Line 4's' started by Turkey, Jun 15, 2017.

  1. Turkey

    Turkey Member

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    The bike is a fzr 3ln, i have had it for a little over a year now and of late it has developed a rough idle issue. It will start and run fine when the motor is up to operating temperature.
    How ever it can be very hard to start of a cold morning, im not sure if this could be related? For example could it be a blocked jet or should i be looking at valve Clarences?
    Since ive had it i have changed the spark plugs and i have replaced the voltage reg/rec, other then that it has been a great little bike.
    Can some one please help!
     
  2. Murdo

    Murdo The Good Doctor Staff Member Premium Member Ride and Events Crew Contributing Member

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    Check the valve clearances before you do anything else so you know they are right.
     
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  3. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Is it a 3LN1 or a 3LN3, 3LN5 ,3LN6 ?
     
  4. Turkey

    Turkey Member

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    The bike is a 3ln5
     
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  5. Turkey

    Turkey Member

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  6. Turkey

    Turkey Member

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    I took the carbs apart and there was a lot of dirt and it looked like old hardened fule possibly as well? I cleaned and blew out the jets both main and idle jet in all 4 carbs. However i didnt go as far as taking out the idle air screw mixture or emulsion tubes out. Could that be the issue with the rough idle and issues cold starting as my efforts didnt really change anything she still wont start in the mornings and the idle could be worse!! Please help its driving me mad. The plugs are new is and i tryed taking off the caps and re attaching the leads but there was no difference. It also has a after market exhaust on it i thought ot might be running a little rich maybe but im not sure the plugs are a little oily but nothing to bad.
     
  7. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    At the bottom of the thread's where the pilot jet's screw in, in the base of the carby, there's a tiny hole that goes through to the main bore of the carb.
    If that's blocked or partly blocked then it'll be hard to start and hesitate when you rev it

    Rough idle is more the mixture screw's and mixture screw adjustment, plus if there is any dirt in there it won't help the fuel to get through
     
  8. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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  9. Turkey

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    This is a little video of the bike just incase im not describing it well, also you might notice it sounds rough if i easy it up the rev range as well. Oh and thanks for the gide for cleaning the carbs i will have to take them off and give it a nother try.
     
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  10. Turkey

    Turkey Member

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    Also would any one be able to tel me how many turns to put on the idle air mixture screws for each carb or are they all the same?
     
  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Mixture screw's are standard at 3 turn's out, then once the engine is at operating temp you can adjust them from there



    I don't think that sound's too far off atm
    Have you synced the carby's ?
    And have you ridden it up the road yet ?
     
  12. Turkey

    Turkey Member

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    Yes i took it out for a blast after putting her back together last weekend, nothing has really changed. Also that video was taken at operating temperature.
     
  13. Turkey

    Turkey Member

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    And no i have not yet synced the carbs i though it could have been the sync a little off but im really not to sure where to start on that? if you could give me some advice on how to sync the carbs i would be great full.
     
  14. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    You really need a tool either bought or diy to sync them properly, the engine sounded a lot smoother in my FZR when i did it

    SSL11411LC.jpg

    20170204_204343_zpsgcubcmli.jpg
     
  15. Turkey

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    So in the jar is that petrol? Also do the pipes just go into the jar? Also where do you plug the pipes into the carbs? And then how do you change what ever it is you need to change?
     
  16. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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  17. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Looking at what was in your fuel bowl's i would be replacing the fuel filter in between the fuel pump and fuel tap.
    Might pay to give your tank a thorough clean out and flush too
    And take the pick up out from the boittom of the tank and clean the 2x filter's on that while you're at it.
    And clean out the fuel tap if you haven't done that already too


    I had water in there with a couple of drops of food colouring to make it easier to see, but it was a bit thin
    If i use it again i'll use some engine oil i think.
    Yeah the tube's go into the liquid, and the other end get's attatched to the vacuum port's on the bottom of your inlet manifold's
    Think i wrote a little about that home made sync tool i made in my FZR thread, the link for it is below in my signature, just click on it to have a read through

    Then when you run the engine it will suck some fluid up the tube's about 1/4 of the way and you can see if one carby is sucking more than another.
    There's adjustment screw's between each carby that you turn a little to get all the fluid level's even in the tube's
    The engine rev's rise when this happen's and then you can drop the idle speed back down to normal.

    As mentioned above you need to check and adjust your valve clearance's before balancing/syncing the carby's, if the valve's are out of spec in one cylinder it will change the vacuum that pot make's.
     
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  18. Joker

    Joker If you want me find Club250 on facebook. Premium Member Contributing Member

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    Nice bike, haven't seen another fizzer with the same scheme as mine in oz.

    Jets can get blocked in a way that compressed air won't fix alone. Try gently scrubbing them with a single wire brush strand, including the pilot holes. Have had got results on my bike with that method.

    If hard to start check pilot screw turns, you might need to make richer (ie turnout). Work in quarter turn increments.

    As originally suggested valve clearances make a big difference so check those too. It's time consuming but not that hard.
     
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  19. Turkey

    Turkey Member

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    Sweet thanks a lot guys i will try syncing the carbs this weekend hopefully and i will post updates, im keen to here her idle a little smoother. Im not sure what its suposed to sound like but my dad has a mc 22 and it doesn't share that chug chug idle. It also is a little easier to start of a morning.
     
  20. Joker

    Joker If you want me find Club250 on facebook. Premium Member Contributing Member

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    Carbs don't magically go out of sync suddenly though, it can be a slow degradation over time and might be required once or twice within a bike's life so I wouldn't think it's a commonly required procedure. I suggest trying other avenues before you spend too much time on something like that, especially if you haven't done it before.

    It may or may not make a noticeable difference, while something like valve clearances (I highly recommend doing this first), new carby seals and a jet cleanout will.

    Good luck either way.
     

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