Sprint St Gen1 3000rpm Idle

Discussion in 'Technical Help' started by John Boston, Nov 30, 2020.

  1. D'Ecosse

    D'Ecosse Senior Member

    Jun 23, 2019
    271
    113
    CA, USA
    Also - on your model, the idle air mass is a combination of air past the 'not-quite-completely-closed' throttle plate and the IACV; One throttle position is fixed by the stop and the other two by the independent adjustments to balance the three together. The balance must be set using vacuum gauges. So 'closed' is not truly absolutely closed. It's conceivable that one or two of the throttles could be mis-adjusted and allowing too much air past them; this would also result in a very lumpy idle however as the IACV fights to try to counter that.

    One very quick test you can do to see how much air is not coming from the IACV - whether that be past the throttles or a leak - close off the intake to the IACV (put thumb over it) - it should stall; if it does NOT stall then it says the air is coming from some other source and you would need to look for the cause.
     
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  2. John Boston

    John Boston Member

    Nov 30, 2020
    28
    13
    Bristol
    Yes, the idle was highway it was from cold, hadn't checked water level so only ran it briefly.
    Have now topped up water/anti freeze and run til warm, idle is around 1200, perfect. Sounds great.
    Put rear bodywork back on, having resprayed the rack. All looks good.
    Then did quick pre mot check and found blown dip beam bulb ( I have twin dip conversion).
    So, change the bulb. Er. Not that simple. Rubber boot off, spring clip and "ping", off it flies. Great.
    So. Front fairing off, headlights out. Spring clip and new bulb in. Then fun trying to fit front fairing on again.
    This bike had had a tough life, it had been down on 1 side (sidecstand issue) when I got it. Fairing panels replaced. I've dropped it at least twice on slippery paving in my garden, so most of the fixing tabs are broken. Needs new bodywork really, but I can't run to that.
    Anyway, it's back together now and rode home. Includes short motorway stretch. All good.
    Forgot to take a photo though. It was dark.
    Now to book mot before I can ride it again.
     
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  3. Sprinter

    Sprinter Kinigit

    Aug 17, 2014
    6,029
    1,000
    uk
    Always good to hear the end of the problem. Well done.
     
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  4. D'Ecosse

    D'Ecosse Senior Member

    Jun 23, 2019
    271
    113
    CA, USA
    Good to hear!
    Just a note on bike being dropped on left side - on that generation, if dropped on that side with engine running, it will suck oil up into the airbox and down into cylinder one through the TB on that side; in extreme case it can 'lock' the engine by filling that cylinder with oil; but at the least it will have a LOT of oil in the airbox which will need to be cleaned out.
    Your bike may not have been running, but just some info if it should apply.
     
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  5. John Boston

    John Boston Member

    Nov 30, 2020
    28
    13
    Bristol
     
  6. John Boston

    John Boston Member

    Nov 30, 2020
    28
    13
    Bristol
    Hi,

    Thanks for the info, but is was dropped long before my ownership. Apart from cleaning out the airbox, which I did when I last changed the air filter, it's probably a bit late as I've owned it at least 5 years.
    Luckily when I dropped it in my drive it wasn't running.

    Thx, John
     
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  7. John Boston

    John Boston Member

    Nov 30, 2020
    28
    13
    Bristol
    Well. Took it for an mot. Slight play in rear wheel bearing and bottom shock link. Bit of surprise as supposedly replaced by fowlers, Bristol a few years ago. Advisers on both.
    Too much fluctuation in front brake pressure. Fail.
    So, quickly ride back to my unit. Calipers off. Pads oit. Pushed pistons out and cleaned with brake cleaner and tooth brush. Cleaned pads and filed edges a little. Much freer. Pit back together. Brakes much firmer and passed.
    Back on the road at last.
    Still didn't take photo as by then was in a rush to my next job.
     
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