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Thread: Loss of power/engine noise

  1. #1
    FaustFest's Avatar
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    Loss of power/engine noise

    Dear all,

    I have a 99' st11 with ~50k miles. I bought it maybe 6 months ago.

    I was riding at a steady speed of ~70mph (engine was warmed up) and I started to notice a loss of power. It would stutter and all of a sudden gain power again and judder forward. I have had this with a previous bike and it turned out to just be a fuel pipe. However, I tried to nurse it home as best I could but a couple of miles down the road I heard a couple of REALLY LOUD bangs that sounded like they were coming from the engine. At this point I pulled over, the engine died and I had to get recovered. The bike will start now, but obviously I am not sure what's wrong with it. It felt like it wasnt running on all four cylinders.

    I am pretty new to Pans but the engine also sounds more noisy to me now, but I am not an expert on how it should sound. I just know it sounds different to me now. I am hoping it is something simple!

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    Upt' North's Avatar
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    Re: Loss of power/engine noise

    More info would be good.
    Bang like a back fire?
    When you re started was there any blue smoke from exhaust.
    What's the oil level like.
    Had you done any work recently.
    Have you had the plugs out to see if they say anything other than loveliness.
    Upt'North.

  3. #3
    Oldbikefixr's Avatar
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    Re: Loss of power/engine noise

    Any other symptoms you noticed?
    -fuel smells
    -over temp reading
    -water or oil leaks
    -water level
    -oil level
    -any indications of overtemp in the wiring around the battery or alternator?
    -what is the corrosion like in the area of the alternator...or around the rear of the alternator?

  4. #4
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    FaustFest's Avatar
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    Re: Loss of power/engine noise

    Hi both,

    I will try and provide as much information as possible.
    Unfortunately due to the fact I wear earplugs I couldn't distinguish the 'bang' very well - except that is was very loud and didn't seem to be associated with any particular RPM or speed, it happened maybe three times in the course of a minute. I pulled over after.
    After pulling over there did seem to be a 'hot smell' that didn't reappear when I started the bike up again. When I started the bike up again there was no blue smoke, or any smoke at all. At no point was the temp gauge over 1/2 during the journey.

    I haven't done any work on the bike recently - all the fluid levels are adequate and within range, there are no visible water/oil leaks.

    I plan on taking the bike apart in the next few days and investigating the plugs and thoroughly inspect the alternator and wiring.

  5. #5
    Site Supporter Uncle Phil's Avatar
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    Re: Loss of power/engine noise

    First stop would be to check your fuel flow. If the carbs got 'loaded up', it could create a very loud backfire.

    97 ST1100 STD +150,000 / 02 ST1100 ABS +114,000/ 97 ST1100 ABS +75,000
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  7. #6
    Slydynbye's Avatar
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    Re: Loss of power/engine noise

    Loss of power makes me think your Fuel cutoff diaphragm is failing. Bypass it and perhaps replace fuel filter before diving in deeper.

  8. #7
    kiltman's Avatar
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    Re: Loss of power/engine noise

    Check the red connector to the main relay. under the left panel. Put it on the Center stand start it, leave it neutral and deploy the side stand, if it shuts off then jump the two green wires on the side stand switch.
    what you describe happens when there is a poor electrical connection at the main relay or shut off switch, the engine may run rough like it’s missing and backfire.
    that’s my take on the situation

  9. #8
    John Heath jfheath's Avatar
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    Re: Loss of power/engine noise

    It is possible that one of the four vacuum hoses has become detached. They are short lengths of black tube that protrude from behind each cylinder head (roughly above the spark plugs) and are used to plug in vacuum gauges when balancing the carbs. In the UK they are capped off. The cap is removed in order to connect the gauge, which saves having to access the connection at the base of each carburettor, way down in the Vee, but it is not unknown for the cap to come off, or the other end to be pulled during a service, to become 'unplugged' at some point in the future. If it is this, you need a flashlight and a set of long nosed pliers to get it back on.

    If one of these comes off, the symptoms are a serious loss of power, a lot of backfiring, and it feels / sounds like it is a cylinder down.

    Sorry, I don't have an 1100 any more and can't provide a picture. Someone else may chip in.

    [Edit]
    Forgot to say - one of the four tubes isn't blanked off like the other three. This is the rear one on the right hand side. It is connected to the petrol shut-off valve - the suction from the engine keeps the valve open. If that is sucking air from outside, the 'petcock' will not be kept open and the engine will not get its fuel.
    [/Edit]
    Last edited by jfheath; 12-07-2017 at 04:33 AM.

  10. #9
    Site Supporter Jim Van's Avatar
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    Re: Loss of power/engine noise

    Interesting problem. Sounds like gas may have been building up in the muffler due to no spark. And then when the spark returns, BAM !!!

    But that's just a WAG, for sure !!!!

    Now that the bike is running, take it for a ride at 60 mph, then turn the RUN/STOP switch to the "STOP" position until the speed gets down to say, 45 mph and then turn the RUN/STOP switch to the "RUN" position and see if the "BAM" occurs. WARNING : Of course you may also damage your muffler by doing this.
    IBA #35372
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    Re: Loss of power/engine noise

    Stupid question...how is your battery? I’ve had 2 bikes (V30 Magna and my 00 ST) with bad batteries and in both cases, when on the road, it would backfire and run terribly. It would have been running on the alternator at that time and a new battery solved everything. Carb issues can definitely be at fault here, but I’d check the voltage of the battery, just to be sure.
    Bob 2000 ST1100/1994 ST1100 ABS

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