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Help FZR250R 3LN5 rough running and slow to rev

Discussion in 'Yamaha 250cc In-Line 4's' started by sumthingdarkside, Mar 31, 2020.

  1. sumthingdarkside

    sumthingdarkside Member Premium Member

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    yea spark at every cylinder, all cylinders are running. have replaced all the spark plugs and have rethreaded the caps on the leads also
     
  2. jmw76

    jmw76 Well-Known Member Premium Member

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    If you remove the plug leads one by one and then start the engine can you isolate the problem down to a particular cylinder or pair of cylinders. I have put new plugs in before only to find that I had a duff one. Have you checked each plug with a megger or multimeter on megohm range. You can check them in the bike. With lead removed, test between the top of the plug and the cylinder head. Anything other than an open circuit is an issue.
     
  3. Wolfgang

    Wolfgang Member Premium Member

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    Hi there,
    I currently have an Fvr400 and am trying to introduce myself and get involved with the Forum. However, I seem to have to sit on the sidelines before i can introduce myself and get involved. Watching threads in anticipation of having to ask questions in the future. Hope you get it sorted :)
     
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  4. sumthingdarkside

    sumthingdarkside Member Premium Member

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    @jmw76 yes i checked the plugs before i put them in and all were the exact same reading on the multimeter, is there any way of testing the ignition coils maybe?
     
  5. jmw76

    jmw76 Well-Known Member Premium Member

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    ???? What was the reading on your multimeter? It should have been 100's megohms or even higher, if you could get a reading at all. If you are getting a really good spark at each plug lead (from lead to cylinder head) then most likely not a coil issue. Were you able to determine which cylinder(s) are giving you problems?
     
  6. jmw76

    jmw76 Well-Known Member Premium Member

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    Humour me. Check your plugs again while in the bike. Report back with all readings if anything other than open circuit (infinite resistance).
     
  7. sumthingdarkside

    sumthingdarkside Member Premium Member

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    @jmw76 checked all plugs in the bike with multimeter set to ohms and all plugs report as open circuit, old plugs that came out all test at ~5k ohms when measured from threaded end to electrode
     
  8. sumthingdarkside

    sumthingdarkside Member Premium Member

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    found @GreyImport 's article on testing the coils,

    primary windings of both coils test as 3.2ohms and cylinder 1,4 secondary was 15k and cylinder 2,3 secondary was 14.5kohms. nothing looks out of the ordinary. While i was in there, there were 2 wires that had been cut, on blue and one blue with red trace both looked like they went to the cluster, would these be for the speed cut?
     
  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I don't think there's any problem's starting thread's here, maybe @GreyImport can have a look, or message you to sort it out?
     
  10. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Working on it :thumb_ups:
     
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  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Here's a couple of question's you need to answer so we can help you sort the issue
    First one is how many turn's out are the mixture screw's set at now?
    The factory mixture screw setting's are ok to get the bike up and running, but they still need to be tuned to suit your engine with the km's it has now, it's no longer a new engine
    You need to warm the bike up to normal operating temperature first by taking it out for a 10 minute ride, then you can tune the individual mixture screw's to get the highest/smoothest idle in each carby (drop back idle speed to 1600 rpm after adjusting each mixture screw)
    A non contact digital thermometer pointed at each exhaust pipe up near the head will help you tune it, try and get the highest temp reading)
    Second question, what is the fuel level in each carby atm ?
    Turn the ignition on and off a few time's so the fuel pump prime's the carby's properly and turn's off straight away when you turn the ignition key to the On position, then turn the key off
    Fit some 3mm i/d pvc hose to each of the fuel bowl drain's and run it up to about the top of the airbox and secure each one.
    Now open the drain screw's on each carby float bowl and you will see fuel run into the pvc tubing and it will travel upward's
    Turn the ignition on and off a couple of time's again to check the fuel bowl's are full, with the pump turning off pretty much straight after you turn the key on.
    Now measure the fuel level's in each carby, they are measured from the line on each fuel bowl and upward's,
    and let us know what they are


    With the exup cable's, how tight are they ?
    eg how much up and down movement in each cable before the wheel start's to turn when you move the cable with your finger



    A couple of other thing's,
    the jet block rubber seal's in these carby's crush and go hard after 20+ year's and the jet block's can leak air, causing running issue's
    Also the intake manifold's will start to perish and get hairline crack's in them after a few year's, it will let air in to the air/fuel mixture making the bike run lean, people try to compensate for the lean situation by richening the mixture screw's but it doesn't really help
    To test if your manifold's are leaking start the bike up and let it idle, now spray some wd40 or degreaser onto the rubber manifold's under the carby's and listen for any change's to the idle, if there is a change then the manifold's are leaking
    The only way to fix the cracked intake manifold's is by replacing them with new one's, luckily there are replacement's available off ebay china now
    They don't last as long as the genuine rubber intake manifold's but they're only about 1/16 of the price of the genuine manifold's

    https://www.ebay.com.au/itm/Carbure...114707?hash=item4d92026e93:g:7CAAAOSwpmhcuErv



    And lastly the corrosion you have in your stator cover and stator, can you post up a picture please ?
    If there's any corrosion between the stator and the engine cover, and between the pickup and engine cover it can cause bad earth's and high resistance so it may not be sending the full / correct signal to the TCI
     
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  12. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Yep Im waiting to hear how a nice cleaned up stator affects the running .... simple things first :cool:
     
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  13. sumthingdarkside

    sumthingdarkside Member Premium Member

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    alrighty bike is back together and running, nothing has made a difference, i have been running it with no airbox and have just noticed that carby number 3 diaphragm slide hardly moves when you give it throttle lags way behind the others. also if i cover carb 1,2, or 4 with my palm the bike will want to stall, but if i cover carb 3 then no change.

    I tried @jimv50 method with a spray bottle and all 4 headers are getting warm but cylinder 3 is noticeably less so.

    So im pretty stumped. Chances of a dropped valve or something? Doesnt smoke at all, starts easy peasy hot or cold, no loud clattering noises as you can hear in the video.

    and sorry @my67xr i didnt get a picture of the corrosion before i cleaned it
     
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  14. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    Sound's to me like your number 3 carby cap is missing it's o'ring

    [​IMG]
     
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  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Then remove the carbs and check the diaphragm in #3
    It may be pinched or is split

    Theres also tiny orings that fall out easy when replacing the top caps

    oring.png
     
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  16. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    This is when my #1 was pinched during reassembly

    pinched dia.jpg

     
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  17. sumthingdarkside

    sumthingdarkside Member Premium Member

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    When i had the carbs off stripped cleaned a rebuilt i checked all the diaphragms and they were in good condition no splits, and replaced those o-rings with the ones from the keyster kits so im 99% sure its not that.

    However for the sake of a sainty check i just went out pulled the carbs up, carb 3 diaphragm is in minty condition and o-ring was in situ

    nice video there @GreyImport i can see the slides not moving, mine moves more than that. Lets say if youre at 50% throttle and all the slides are even then slide 3 will be only at 25% open
     
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    Last edited by a moderator: Apr 3, 2020
  18. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    You need to work out why the carby is not getting vacuum from the engine then ?
    Is the carby manifold clamp tight ?


    Might be time to compression test it ?
     
  19. sumthingdarkside

    sumthingdarkside Member Premium Member

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    Yea im thinking compression test or inspection camera down the plug hole. Just seems weird that something to cause the cylinder to have no/low compression or leaking valve, yet it stills starts and runs and idles like it always has, bit of choke when cold and it fires right up and starts on the button once it has some heat in it.

    I would think if it had dropped a valve or broken a ring it wouldnt want to start, let alone idle and rev and would also be blowing heaps of smoke? or am i mistaken? Also surely there would be a big clattery noise?

    I'll have a further look into the carb manifolds, do they have some o-ring or something that seals them to the head? they look fine if not a bit aged from the outside.

    Might struggle to find new ones being in lockdown in nz at the moment so anymore troubleshooting might have to wait for another 3-4 weeks at the earliest. Might have to bring this thread back from the dead later on.
     
  20. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    A broken ring might start smoking once it wear's a groove in the bore.
    A valve may be burnt and not sealing properly.
    They can start and run on 3 cylinder's if a coil lead is faulty, a spark plug cap get's corrosion inside, or a spark plug foul's
    If it's just a burnt valve then it'll run with little or no compression on the cylinder without much smoke, just unburnt fuel.

    A dropped valve could do all sort's of damage to the piston, combustion chamber, bore etc, that'll make some smoke if it stay's running


    Manifold's a bit aged on the outside, it take's a lot less than this to cause drama's

    fzr250 intake manifolds.jpg


    And all of these below leak
    fr250r intake manifolds.jpg
     
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    Last edited: Apr 3, 2020

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