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Thread: Engine problems - irregular engine speed

  1. #1
    Join Date
    Jun 2017
    Location
    Sweden
    Posts
    1

    Default Engine problems - irregular engine speed

    Hi. My ducati 851, 1989 has rolled 70000 km. The engine has always run smoothly, but lately the engine has begun to go irregular when it is not loaded. I have a very smooth and safe idle speed, and when I load, the engine pulls even and strong. The problem arises when I slow down tex to a roundabout at the road and have even, non-stressing gas, and the engine starts to jerk, which also increases. I increase the gas ending the jerk, and I reduce the gas and the engine brakes stop the engine jamming. No fault is heard from the exhaust pipes. I've had this problem with a irregular engine once a time before, and then fixed it by replacing fuel filter.
    Current measures: New spark plugs, clean air filter, new fuel filter, cleaned and controlled injection, replacement of power group amplifier control unit, replacement of I.A.W. Electronic central unit.
    Unfortunately no difference!
    Able to change or adjust: Pressure Regulator, Absolute pressure sensor, Coil, synchronize injection, Synchronize Throttle Position Potentiometer.
    Is there anyone on the forum that can give me information about where to look first?
    Thanks, Magnus Sweden

  2. #2
    Join Date
    Dec 2012
    Location
    Netherlands
    Posts
    1

    Default 851 Strada 1992 68000km

    Hey,

    I'm experiencing similar problems. MOst of my rides (cold engine) It runs fine, also at constant low speed. after a while when the engine is warm it starts.
    Constant speed is very difficult, feels like constant misfiring the enigine. also the exhausts bangs now and then (explsions in the exhaust)

    I tried swapping the relais in the rear without succes, hope that someone can help.

    regards,
    Rob

  3. #3
    Join Date
    Oct 2010
    Location
    Newcastle Upon Tyne UK
    Posts
    104

    Default

    My bike has had a similar problem for quite a while and I have tried just about everything I can think of without success - fuel filter and lines, had injectors tested and cleaned, balanced throttle bodies, reset tps, swapped over ECU etc etc but nothing has fixed it and I have just learned to live with it for the time being.

    If you find an answer then please let me know what I have missed!

  4. #4
    Join Date
    Jun 2007
    Location
    Melbourne, Australia
    Posts
    1,389

    Default

    chain tension/wear, closing clearances, mixture, throttle cable slack?
    Brad The Bike Boy

    www.bikeboy.org

  5. #5
    Join Date
    Oct 2010
    Location
    Newcastle Upon Tyne UK
    Posts
    104

    Default

    Brad, yes - all have been checked.

    It does seem odd that so many early 851s seem to have similar problems and I wonder if it could be something like coils starting to break down under load due to age?
    Like others mine is worse when it gets hot.

  6. #6
    Join Date
    Jun 2007
    Location
    Bris Vegas
    Posts
    3,484

    Default

    A long shot, but fly wheel could be moving.
    Griff
    To infinity and.......

  7. #7
    Join Date
    Oct 2010
    Location
    Newcastle Upon Tyne UK
    Posts
    104

    Default

    Griff - is there any easy way to check for that?

  8. #8
    Join Date
    Jun 2007
    Location
    Bris Vegas
    Posts
    3,484

    Default

    Alternator cover has to come off. Has it had a sprague clutch change?
    Griff
    To infinity and.......

  9. #9
    Join Date
    Oct 2010
    Location
    Newcastle Upon Tyne UK
    Posts
    104

    Default

    Yes, I replaced the sprag clutch at the end of last year but the irregular running was exactly the same before that - it has been a problem for quite some time that I have just learned to put up with as the bike runs fine when on the open road and on and off the gas - it is only really a problem at low speed on a steady throttle opening.
    I guess the real answer is to get it on a dyno with a good operator to see what is happening to the mixture but that will have to wait till next year as I am laid up with a crocked back at the moment!

  10. #10
    Join Date
    Jun 2007
    Location
    Bris Vegas
    Posts
    3,484

    Default

    At what rpm are we talking about here?
    Griff
    To infinity and.......

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