4th Gen idle hangs

Discussion in '3rd & 4th Generation 1990-1997' started by dgp, Mar 2, 2021.

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  1. dgp

    dgp New Member

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    Hi everyone,
    I’m new here and have just picked up a 1995 model with 73k on the clock.
    I am looking for some assistance to point me in the right direction in fixing a hanging idle before I make a mistake I might regret.
    The bike starts fine on choke, but if you blip the throttle on choke, it bogs down and wants to stall.
    When the bike is warm, no choke, when changing gears, the revs do not come down quickly as they should, they hang at about 2k and drop slowly back to idle. This of course makes changing gears an issue, as the idle is too high when selecting the next gear while cruising around.
    I have read a lot on these pages, I am not a mechanic but am no stranger to tools.
    I figured it may be a vacuum leak so was going to start chasing that first, but I did read that this condition spikes the idle, so possibly not the issue.
    I bought the bike of an older rider who had not started the bike in over 12 months. It was running rough so they had their mechanic drain the fuel and refresh it. That didn’t seem to help. I don’t know what the mechanics diagnosis was, and perhaps that is the reason the bike was sold.
    Should I start with a valve adjustment and then move on to pulling the carbs for a clean?
    I am not familiar with working on carbies so don’t really have an understanding of where all the internal passages go.
    I downloaded the workshop manual so that is a help.
    I do understand the rich/lean conditions but have to think about it a bit to be clear.
    I don’t understand how the carbs move from the idle circuit to the main jets though.
    Any help or pointers will be appreciated.
    Thanks
    David
     
  2. iLikeThat

    iLikeThat New Member

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    Sound like a vacuum leak yes, how the bike reacts to a vacuum leak may differ with how much and what conditions it is getting. Would try to check the throttle body's for cracks and leaks. You can try spraying starter gas around the boots to check for differing idling. If the idle spikes you have a leak and the bike is pulling false air in which results in weird conditions.
     
  3. dgp

    dgp New Member

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    Thanks iLikeThat, I will start by looking for a vacuum leak.
     
  4. jethro

    jethro New Member

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    I would start with a strong tank mix of Chevron techron fuel system cleaner. With the bike running the techron will clean things up nicely and you don't have to take the carbs off. If the bike isn't running then the carbs for sure need to come off. If you don't find a vacuum leak I would see where the carbs are as far as sync goes. Carbs way out of sync can do terrible things running wise.
     
  5. dgp

    dgp New Member

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    Thanks jethro, i will certainly try the fuel system cleaner before i start pulling things apart.
     
  6. upwinger

    upwinger New Member

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    If you don't have a carb synchronizer, you can make your own with a yard stick, clear plastic tubing, some plastic or brass tee's and some 2 stroke oil.

    Sent from my Pixel 3 using Tapatalk
     
  7. dgp

    dgp New Member

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    Thanks for the tip upwinger, but i have a carbtune on the way, might take a while though with COVID :(
     
  8. dgp

    dgp New Member

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    But of an update, I used aerostart to spray the manifold insulator boots with the bike running, and the revs jumped when I sprayed both front cylinder boots.
    The clamps were tight, so no option but to remove carbies. The boots are rock solid, no wonder they didn’t seal. I have ordered replacements.
    While everything is apart, I have given everything a really good clean, removed the radiator, and am also undertaking a valve clearance check, I have made another post about this as I have questions specifically related to the timing and cams removal.
     
  9. dgp

    dgp New Member

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    Hi all, some more updates.
    I am slowly cleaning the bike and carbs while I wait for some parts to arrive. I have ordered new manifold insulators, jets, bowl gaskets, needle valve and some o rings.
    #1 carby
    Idle jet blocked
    Emulsion tube blocked (used the 0.012” guitar string trick)
    #2 carby
    Idle jet partially blocked
    Emulsion tube partially blocked
    #3 carby
    All clear
    #4 carby
    Idle jet blocked

    All jets are standard Keihin
    All diaphragms are in good condition, I couldn’t figure out how to seperate the needles from them though.

    I have a few questions about some of the components of the carbies, pictures below,
    1. What is this solid copper tube in the float bowl?
    2. Is the needle seat replaceable or you just put a new needle in?
    3. What are these, what part do they play in the operation?
    4. I have an Omrae slip on, do I need to change jetting from the standard idle-40, and main-125?

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  10. squirrelman

    squirrelman Member

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    ^^^ with rubber-tipped needles the seats don't suffer wear. #3 are air corrector jets used to fine tune fuel mixture at higher air velocities. unless you are installing jet kit needles, no need to remove them from slides.

    rejetting for new muffler is a good idea, and how much needs experimentation or a couple of dyno runs.
     
    Last edited: Mar 11, 2021
  11. dgp

    dgp New Member

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    Thanks squirrelman.
     
  12. dgp

    dgp New Member

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    New jets, gaskets, bowl drain screws. Gave everything a nice clean before re-assembly.
    Hooked up the drip, no leaks.
    Waiting on the new insulator boots before I can put back on bike.
    Also waiting on shim kit so I can do the valves before I put the carbys back on.
    Secondary air filter is non existent.

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  13. COS_VFR

    COS_VFR New Member

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    You shouldn't need to remove the needles from the diaphragm, but if you want to, page 6-20 of the service manual shows how.
    VFR_service6-20.png
     
  14. squirrelman

    squirrelman Member

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    i don't recommend removing needle from slide as the plastic there is weak and there is risk of damage. above diagram may not be correct as far as i know since the slides i've dealt with have a plastic 8mm nut as part of the top of the slide.
     
  15. dgp

    dgp New Member

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    Thanks guys, I don’t know how I missed that in the manual.
    I have buttoned the carbies back up and am waiting on my insulators before I can reinstall on the bike.
    My shim kit turned up but all the shims have a layer of rust on them, so they have to be returned and new ones sent out, further delaying the process.
    Anyway, gives me time to repair some fairings and re grease the head stem bearings. I have also ordered new fork seals, bushes an guides, but they are on back order from Japan so will just replace the oil for now until the bits come in.
     
  16. dgp

    dgp New Member

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    One of my needles did have a suspect area though where it has worn very shiny, there is no discernible indentation on the needle though.
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  17. squirrelman

    squirrelman Member

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    how many miles on your bike ?? head bearings are usually shot and needing replacement by about 35k miles. be sure to wash out the forks with solvent two or three times.
     
  18. dgp

    dgp New Member

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    The bike has 45k miles, 73k km’s on it. I’ll pull the head stem and check, but looks like I might be up for bearings too.
     
  19. dgp

    dgp New Member

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    Well, massive f-up from me last night, I was completing the valve shims, buttoned up the rear inlet cam, re-checked and needed to replace one of the new shims, so removed the cam again, and when I re-installed it, the cam did not seat correctly, and I snapped it in half.
    I think what happened is the secondary gear on the cam, that I assume prevents backlash, did not mesh correctly with the drive sprocket which then applied undue force when I did up the cam retaining bolts. And I was bloody careful too, going in the pattern specified in the workshop manual, I must have touched each bolt at least a dozen times during the process.
    What’s the deal with those smaller tooth gears, nothing about them in the manual, how do you ensure they are aligned to the gear drive?

    Needless to say, I’m devastated by my mistake.

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  20. squirrelman

    squirrelman Member

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    sad story :(

    you must have had some warning that things weren't going back together correctly when too much torque was needed on the socket drive. using a torque wrench ??

    the smaller spring-loaded gears naturally line up with the cam gears with a little fiddling and snap into position, although a bit of alignment might be needed with the point of a screwdriver.
     
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