Sudden High revs when cold starting in traffic

Discussion in 'Mechanics Garage' started by 34468 Randy, Oct 1, 2017.

  1. 34468 Randy

    34468 Randy Secret Insider

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    This is a cut an past from the What have you done for your VFR today thread. There is also a conversation going on in private messaging where it does not need to be private. I thought it should be addressed here with its own thread in the garage. Everyone's input is welcomed while I have my poor pony hunkered down in the Honda Stables.


    I really don't think it is a big issue. Just fond the issue.

    This may be over simplifying the issue but what is happening is that when cold, and starting off from a start in first gear, the bike will suddenly rev up to about 5 K and will launch me if I don't get right back on the clutch like, really fast. Bad enough for this to happen when you are going straight through, but if you are turning a corner, it is frightening. After it has done this a couple times, the problem goes away for the rest of the day for the most part. I have changed the wax sending unit to no avail and the bike is now in the shop. Honda Canada has no solutions for the tech.

    So, I apply reasoning to this and this is what I come up with:

    1. The bike is cold and when the clutch is let out, the sudden surge in RPM.
    2. This surge is consistent with the letting out of the clutch
    3. It does not take a genius to figure that RPMs will not increase if there is no fuel supply increase so there is a sudden release of fuel to the engine when the clutch is released.
    4. Whatever it is in the engine that tells the fuel to increase has told the fuel to get the lead out and flood through those injectors
    5. The bike is EFI so something is telling the injectors, "Hey...prepare. Fuel on the way"
    6. But this is only when cold so "Hey injectors, it is warm so no flooding of fuel for you today"
    7. And once it has done this a couple times in immediate succession, then the issue disappears for basically the rest of the day.

    So, my thinking is that something electronic in the bike, that is connected with the injectors, is fucking with my mind.

    Feel free to offer up your opinions. I may take them to the tech and offer them to him too. However, he will likely check anything I suggest, and of course, $$$$$,

    BTW. This did not suddenly show up after I did or had work done on the bike. It was a gradual thing that at first I thought was my imagination to increasing in intensity and consistency.
     
  2. Terry Smith

    Terry Smith Member

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    This is an interesting one Randy. Interesting for me, expensive for you....sorry about that. The more I think about this, the less I am inclined to believe the wax unit would be the culprit, although it is the one item which should be doing something different (i.e. opening the starter valves) when the engine is cold.

    When idling with the clutch pulled in, the flapper ought to be open, then when you release the clutch it should shut in response to the clutch switch opening. I would assume at the same time you are opening the throttle. I can't imagine that the flapper itself would cause any meaningful change in airflow restriction at low revs, so I would rule that out, but maybe its actuation system is the source? Do you know whether the flapper is functioning correctly?

    To get the increase in revs, you need to be getting a surge of airflow down into the engine, normally this is only controlled by the combination of the starter valves and the throttle plates. Any other air leakage path would cause a faster idle as well. I know on the flapper valve system there is a one-way valve that allows vacuum to be drawn from intake port #2 to drive the flapper via the solenoid; if the hose/solenoid were faulty then the action of the solenoid closing the flapper might trigger a surge of airflow at that point.

    Anyway, lots of idle speculation on my part, but I think the starting point should be inspecting/replacing the rubber vacuum hoses, and maybe the manifold rubbers as well. Your description does sound like a part failing with age/use.
     
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  3. 34468 Randy

    34468 Randy Secret Insider

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    We still talking about the bike here right? Cause I understand this issue quite well.

    I will share this with the tech. The bike has been ridden in some pretty nasty weather year round here in the land if igloos and politically correct politeness.
     
  4. Terry Smith

    Terry Smith Member

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    Yeah, me too!
     
  5. duccmann

    duccmann Member

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    Well hopefully they check the ECU tomorrow--- had to change mine at around 30k-- kept throwing codes with nothing wrong--


    Sent from my iPhone using Tapatalk
     
  6. carlgustav

    carlgustav New Member

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    I'll have to follow this thread as I have experienced a similar issue with my 07. Only when cold, leaving the house, or leaving work after bike parked all day. The RPMs will ramp up quick, as if I gunned her. Have to be quick on the clutch when it happens :rolleyes:. In my case, I noticed some wear on one of the throttle cables where it passes under the bottom of the ignition housing, and started thinking the cable might be catching there just enough to get pulled momentarily. I've been paying more attention to that and haven't had a re-occurrence of RPM surge in a while. Now that I've 'said' this, it'll happen to me again b/c that probably isn't the cure ...

    ACE
     
  7. thtanner

    thtanner New Member

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    Potential sticky injector?
     
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  8. 34468 Randy

    34468 Randy Secret Insider

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    Lets keep in touch over this Carl.
     
  9. carlgustav

    carlgustav New Member

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    Will do. Although I'm old and forgetful ... :D.

    ACE
     
  10. PawnBoy

    PawnBoy New Member

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    Would extra fuel fuel alone really get the engine to rev up past 5K? I'd have thought the throttles would have to open to burn that much fuel. Otherwise, could bad readings from the O2 sensor get the injectors to deliver significantly more fuel?
     
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  11. duccmann

    duccmann Member

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    So Randy your goin to talk to the shop today right?


    Sent from my iPhone using Tapatalk
     
  12. 34468 Randy

    34468 Randy Secret Insider

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    Tomorrow. Working on a barge in Burrard Inlet for 14 or so hours. Will take screenshots of suggestions here to the shop tomorrow when I am off work
     
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  13. 34468 Randy

    34468 Randy Secret Insider

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    I went in today and spoke to the tech. This is still unresolved. He has been searching for solutions on line, including here. I gave him the thread title for him to see as I think there are some great opinions here he can consider.

    For that reason, I took the liberty to copy and past an entry to another thread from OZ VFR and copied it here.

    "That's a wierd one mate.
    The wax unit moves really slow, so that is out of the question.
    When cold a few things are under control on a 6th G, the fuel, the flapper and the VTECH.
    Is your clutch switch working? Have you checked inside the air box?
    It is always a worry when a shop has hold of it, with luck they keep you informed of progress.
    I'm sure other ideas will pop up here."

     
  14. JamesHambleton

    JamesHambleton New Member

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    I'd guess and say that it's bad ground from the clutch switch and it's going back through the circuit, maybe it could be something else like a bad wire by wire sensor? I don't know anything about your model so it's a shot in the dark.
    Maybe worth bypassing the airbox and exhaust sensors as they're used to adjust the mixture, or even clean them up to prevent a false reading (this was happening on my mums car)
    Though I'd guess it's possibly the auto choke coming on, maybe worth checking for any trapped or snapped wires or trying it and having the handle bars at different positions to see if it makes any difference.
     
  15. mlap5150

    mlap5150 New Member

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    Isn't it normal behavior for the RPM to go up a bit when letting out the clutch (at least when cold)? Not to 5k obviously, but I noticed on mine it'll creep up towards 2k without any application of throttle. Not sure what controls or causes that but maybe the dealership can find out.
     
  16. slovcan

    slovcan New Member

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    Hi Randy,

    I doubt it is vacuum related. There are a LOT of bikes here that are way older than yours and the rubber is still serviceable. However, with your mileage I fully expect it to be an electrical issue. Maybe a bad ground as was mentioned or maybe, more likely, a sensor. In a car I'd suspect the throttle body (the rheostat part of it). I don't know how the throttle bodies on bikes send the signals to the ECU. I would look at sensors with moving parts first. The worn throttle cable sounds interesting, too, but I don't see it causing a ~3000 RPM sudden surge under load - no load, maybe. Otherwise, the usual suspects - grounds, frayed wires, dirty/corroded connectors.

    If you took it to Darwin at 3D Cycle, say hi to them for me.

    Cheers,
    Glenn
     
  17. SweViffer

    SweViffer New Member

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    Correct me if I'm wrong, but just more fuel wont make the engine surge. It will actually have the opposite effect, in flooding the engine and make it run worse. You need both air and fuel for it to surge.

    My guess would be sticky throttle plates, broken vacuum somewhere or maybe something like sticky starter valves.

    I don't really buy that the throttle cable is broken, since it wouldn't be affected that much from a warm engine. More likely, in my opinion, to be the actual throttle body assembly. But as I said, just a guess.
     
  18. 34468 Randy

    34468 Randy Secret Insider

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    Agreed. I was being very general in the statement about the fuel. Read in "Whatever fuel and or air it takes"
     
  19. duccmann

    duccmann Member

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    Here ya go Randy but it's in IL

    [​IMG]



    Sent from my iPhone using Tapatalk
     
  20. 34468 Randy

    34468 Randy Secret Insider

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    Gawd! If that doesn't give me the damndest tooth ache!
     
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