99 vfr has vibration around 5k rpm

Discussion in 'Mechanics Garage' started by Emre, Apr 25, 2021.

  1. Emre

    Emre New Member

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    Hi all, I have 99 vfr 800, it vibrates around 5k rpm. It is around 4800-5500 rpms. This rpm range is sweet spot for EU high ways at 6th gear, means 120kmh and it annoys me.

    Also my bike always starts at thirth try when engine is cold and definately doesnt like under 3k rpm. I switch to lower gear if it is under 3k rpm but there is nothing to do if it is on fisrt gear.

    so is it a problem or not? Should I check some parts?
     
  2. Diving Pete

    Diving Pete Member

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  3. Emre

    Emre New Member

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    You mean valve sync?
     
  4. Diving Pete

    Diving Pete Member

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    yep, also when did you last change / check the plugs?
     
  5. Emre

    Emre New Member

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    I changed the plugs just 800km before, they are new. But didn’t solve the problem, btw they were in bad shape.
     
  6. Diving Pete

    Diving Pete Member

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    People more used to it than me may mention the FPR...

    Its a relatively common issue on this model I understand.
     
  7. squirrelman

    squirrelman Member

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    missing tank rubber buffers can cause resonance in the fuel tank and vibrations. also, a worn chain is a possible source, so get the real wheel up to check for a series of loose-then-tight chain tensions as the wheel turns. how many miles on the old girl ?
     
  8. Simon Edwards

    Simon Edwards New Member

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    "so is it a problem or not?" Yes it is. These V4 are silky smooth when working properly.

    120Kph is in the area for 17" and 18" wheel vibration. Have they been balanced recently? Have you lost a balance weight?

    Does the same vibration also happen in lower gears at ~5K rpm?

    You mentioned plugs being bad condition in another post. What do you mean by that?
    Are they...
    Black and sooty?
    Dark brown?
    Light brown?
    Or too white?
    Do they have different colours across different plugs?
    Are the electrodes melted, or have they eroded to larger gaps?
    Any idea how old the plugs were?
     
  9. squirrelman

    squirrelman Member

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    ^^ simon is spot-on. poor wheel balance is a likely suspect.
     
  10. Simon Edwards

    Simon Edwards New Member

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    I forgot to respond to this section of the OP.

    If the plugs are new and correctly gapped, then the fuel/air mixture is the next suspect.

    The cold start issue, coupled with the affected RPM range, appears to indicate the low speed mixture and the enrichment (choke) potentially being an issue.

    Is the air filter clogged? That would affect both of these.

    Isn't the choke automatic on the '99? If so the temperature detection and its effect on the bits its connected to would be where I would start with that.

    There are quite a few threads on automatic choke issues. I'd first take a walk through those threads. Then take a look at the connections on the bike.
     
  11. Emre

    Emre New Member

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    DABC555B-7138-4DDB-8B09-8AEC8AA5AB63.jpeg
    Thanks for help!

    vibration doesnt happen lower gears and tires are really old, front is 9 years old! Thread dept is still good previous owner didnt drive her I think:) so first thing, I will replace tires.

    milage is 44k km around 30k mile. I dont know maintenence history and I dont know the ages of previous plugs.

    I took photo when I replace plugs, I attached it.

    Start issue was there even with old plugs or new Doesnt matter for start issue.

    I always try start with full choke, it is manuel on 99’. Despite the full choke, it starts min 3rd try.

    I just bought tool for measuring starter valves pressure. I hope, problem is caused by valves pressures:)
     
    Last edited: Apr 29, 2021
  12. Diving Pete

    Diving Pete Member

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    My gut feel is your bike has had limited servicing - lol.. Thats more due to when they work, they just work.

    Crazy question, When cold does it start ONLY with full choke? As in, have you tried no choke? I'm still leaning towards the FPR however injectors may also need a clean.
     
  13. Simon Edwards

    Simon Edwards New Member

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    I'll second that suspicion. Also that is a very sensible question. The angle on the plug photos didn't show the central insulator, but the tip looked pretty coked up. Lots of sooty black as if it been running very rich for a while. If its that rich in general running it could start on as little as half choke or even less from cold. I'd bet the fuel ecconomy is not too good at the moment.

    We don't know the state of the air filter. If its really clogged it could also be causing the over-rich fueling.



    The new tyres will almost certainly solve the vibration issue.

    It is not happening in other gears. So it is an issue in a particular speed range rather than an engine issue.

    Just please make sure that they are properly balanced when they are fitted, or it will happen again even with new tyres.

    Please be aware that it could happen at a slightly different speed with new out-of-balance tyres if they get it wrong.

    Resonance vibration like this is dependent on the frequency of rotation (so, speed) plus the overall wheel and tyre combination and the amount of rotational inbalance. Different tyre types have different weights plus differing types and stiffness of construction. These will all change the resonant frequency slightly. However the resonance vibration will usually fall within the same general speed range for a given size of wheel.

    Now you have experienced it you know what to look out for and you will know it when you next feel it happening.

    The simplest test for this is... Does it smooth out again at faster or slower speeds? If so its almost certain that the wheel(s) are not balanced and that it is not a critical engine or chassis issue.

    Having said that it takes some mental strength to go faster from some of these vibrations to test the theory when it could already be trying to shake your teeth out.

    Now, you could simply have the current tyres re-balanced but for two reasons its probably best to replace them...

    1) All the tyre manufacturers claim 10 years of life is safe, but after that they won't claim safety as the aged and hardening inards could delaminate, which you can't see from the outside. At least not until it goes "pop" in a hurry. Usually when under stress, at speed.

    2) If it has been sitting in one spot for a long time, or even two or three spots over a long time, it can develop "flat spots" where the tyres rested on the ground. Sometimes these can flex back out after being ridden for a while, but sometimes they are permanent. These would create some vibration at all speeds, probably quite small ones. But in the typical resonance speed range between 105-130Kph they would give the same vibration as a poorly balanced wheel.

    So, now you have another problem - which tyres to buy. But that is a whole other question, probably best left for another thread.
     
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  14. Emre

    Emre New Member

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    I agree, I did some maintinance but needs pro’s hand, I think.

    btw, I tried to start without choke, it starts after 3rd, 4th kick. But rev remains under 1k for a time, barely contain engine keeps up. Idle rev goes higher over time.
     
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