Revving

Discussion in '6th Generation 2002-2013' started by Jarman83, May 13, 2022 at 10:21 AM.

  1. Jarman83

    Jarman83 New Member

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    Has anyone resolved the revving when cold issue 2007 vfr. Thanks.
     
  2. skimad4x4

    skimad4x4 "Official" VFRWorld Greeter

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    Hi and Welcome to the MadHouse.:Welcome:

    That really is an intriguing first post as I am not sure what "revving when cold issue" you refer to.

    All I can say is that when I traded in my 6th Gen(for an 8th Gen) it had well over 200,000 km on the clock and had proved to be a fabulous mile munching machine.

    Like any machine if you want it to perform well and really last, then it is not a great idea to thrash a motorbike whilst the engine is cold, indeed it is common for the ECU on many modern motorbikes (not just VFRs) to be programmed to restrict performance until the engine is up to temperature.

    On a 6th gen the additional power from the vtec system is intentionally prevented whilst the engine is too cold - this is entirely normal and not an "issue" as such - it is the ECU doing what it is programmed to do.

    PS Please find time to tell us a bit about your riding history and your interest in VFRs. If you already own a VFR post up a photo or two - as the folks on here really like photos. It is easy just click the "Upload a file" link and follow the prompts to select and upload an image from your computer.

    Take care ATGATT


    SkiMad
     
  3. Jarman83

    Jarman83 New Member

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    Hi. Thanks for the reply. The issue I'm trying to explain is. When starting from cold and set off riding. If I come to a set of red traffic lights come to a stop pull the clutch in whilst in gear the bike will rev to about 4,500 rpm. Once the bike gets to running temperature the problem goes away. Have you any thoughts. Thanks
     
  4. Terry Smith

    Terry Smith Member

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    Most likely caused by the fast idle wax unit, there is an adjustment nut where this pulls the starter valves open, yours may need to be backed off a bit. It's meant to be unadjustable and factory set, but perhaps not in your case. Happens with the ST1300 as well, which uses a similar cold start system.
    https://www.st-owners.com/forums/threads/cold-idle-at-4-000-rpms-need-help.31374/

    The FIWU is heated by engine coolant and changes its length as the temp climbs, in the same manner as the thermostat. When stone cold, the FIWU holds the starter valves open to give a fast idle. When the coolant gets hot enough the FIWU will close the starter valves until their position is determined only by the idle screw. The idle screw has no effect on revs when the engine is cold, and the FIWU has no effect on revs when the engine is hot.
     
  5. Grum

    Grum New Member

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    When did this problem happen, was it suddenly after a service? Was it after a coolant change? Does the Idle RPM return to normal 1200rpm once warmed, and there are NO fast idle issues at normal temperatures?

    Generally speaking, in very cold climates it's good practice to let the engine warm up a little before heading off.

    If it's ONLY an issue at cold temps, as Terry mentions it most likely will be the FIWU or its adjustment.
    Perhaps there is a blockage in the coolant flow to or from the FIWU. If you are able to remove the air box, you will be able to see the FIWU in operation and its action on the Starter Valves slowly moving towards the warm idle stop position.
     
    Last edited: May 14, 2022 at 4:11 PM
  6. Jarman83

    Jarman83 New Member

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    Thanks for the reply. It started happening when I pulled the bike out of the garage after sitting doing nothing during the winter months. It only happens when the bike is below normal running temperature. No issues at all once at running temp.
     
  7. Terry Smith

    Terry Smith Member

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    The idle speed is totally controlled by air reaching the cylinders and should be managed by the starter valves, which are small air passages that go around the main throttle butterflies. he butterflies are fully closed at idle. To get a fast cold idle, the wax unit holds the starter valves open and then slowly releases them as the coolant heats up. If you are getting a high idle condition then it is most likely that the wax unit is keeping the starter valves open longer than is desirable.

    One possibility is a blockage in the water hoses leading to the FIWU, or within the unit itself. They are small diameter hoses and more prone to clogging than anywhere else in teh cooling system.

    If the coolant flow stops, then the high idle will persist until you get enough radiant heat soak onto the throttle body area to cause the FIWU to get hot and slow the idle. If you trace the water hoses to/from the FIWU you could disconnect them and see if you can force water through the system (it should flow readily). I've read of using some compressed air to blow out any blockages.

    cooling.png
     
    Last edited: May 17, 2022 at 5:47 PM
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