hesitation when the engine is cold

Discussion in 'Motorbike Technical Discussion' started by Mike, Apr 16, 2005.

  1. Mike

    Mike Guest

    Still working with my virago, i just finished adjusting the valves to
    the proper specs, turns out they were a little tight, but now they are
    definitely in proper adjustment. Now, however, when i start my bike
    after it has cooled for a few hours it will hesitate and cut in and out
    just above idle. As i accelerate the hesitation goes away until i slow
    to that lower rpm range again. After about 3 miles of riding the bike
    stops hesitating at all and runs great. Is this hesitation simply the
    result of a cold engine, or is there something else i should be looking

    Thanks for your input once again.

    Mike, Apr 16, 2005
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  2. Mike

    fweddybear Guest

    Still working with my virago, i just finished adjusting the valves to
    Sounds like you need to adjust your carbs slightly.... but before you
    fool around with them, when was the last time you changed your spark plugs?
    or your air filter? Worn or bad plugs will tend to make a bike symptom like
    this... check plugs first... maybe even change them.. when my bike starts
    hard, a new set of plugs will make the problem go away even if they look
    good to my eye.

    good Luck

    fweddybear, Apr 16, 2005
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  3. Mike

    Calgary Guest

    I get a little hesitation or a flat spot out of mine when it is cold.
    If it only lasts for a few minutes or a few miles I don't think I
    would be concerned.

    Mine smooths out after five minutes or so.

    Don Binns

    2000 - Yamaha Venture Millennium Edition
    84 - Virago 1000

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    Calgary, Apr 16, 2005
  4. Mike

    Paul Elliot Guest

    Hi Mike, I'm going the throw in my vote with the others. It sounds
    fairly normal, these biles were set up to run very lean for low
    emissions and that results in a cold blooded bike. Did this behaviour
    become suddenly worse, or just after restoring the valve settings? Did
    you change any of the carb settings as well? It may be possible to
    slightly enrichen the mixture, but you may lower you milage and increase
    emissions as a result.
    Best of luck
    Paul Elliot, Apr 16, 2005
  5. I see that you've been having what looks like caburetion problems for
    about two years now. Have you recently removed your carbs for cleaning,
    or not. You were told about carb cleaning solutions before,
    did you ever use any of the cleaners that were recommended?

    I would suggest buying a can of Berryman's B-12 Chemtool. A pint of
    that stuff (the liquid, not the aerosol spray) will cost you less than

    On a day when you plan to burn most of a tank of gas, add about 3
    ounces of B-12 to the tank and ride the bike fairly gently. B-12
    contains alcohol and acetone that will wash the lubricating oil film
    off your cylinder walls if you use too much of it, and you don't want
    to overheat the engine or run at high RPM with B-12 in the tank...

    What you really want to do with that stuff is ride at a moderate pace,
    and even slow down and putt along with the engine at idle or just
    above. It's OK if the engine is surging a bit, and the bike speeds up
    and slows down. Just keep your eye on the mirror and be ready to get
    out of the way of cars overtaking you...

    If the B-12 does its job, you'll notice that the idle RPM is higher.
    That's because the B-12 cleaned out the idle jets and idle passages.
    You may have to keep setting the idle speed lower and lower. That's
    good, you're cleaning everything out of the carbs...

    Sometimes, though the idle jets are so plugged up with gum and varnish
    you have to use the aerosol version of Berryman's B-12 to spritz out
    the jets...

    Before I would remove the carbs to get the float bowls off and drill
    out the EPA plugs so I could remove and thoroughly clean the idle
    mixture screws, I would squirt the B-12 into the small hole in the carb
    mouth that's opposite the starting enrichener. The hole I'm talking
    about is the air intake for the idle mixture circuit. If you squirt
    B-12 through that hole while the engine is running, whatever gets
    through the hole will be burned by the engine. The B-12 will go three
    ways. It will go into the float bowls, it will go through the idle
    bypass port, and hopefully, it will clean the critical orifice that the
    idle mixture screw controls...

    If the B-12 cleans that orifice out, the engine will idle at a higher
    RPM than it was before you sprayed it in there...

    If you can't get the idle circuits cleaned out by the two above
    methods, you will need to remove the carbs for thorough cleaning and
    drilling the EPA plugs out and removing the idle mixture screws...

    I've described this process about 100 times now. You can find it if you
    google up "[email protected] +EPA +idle mixture"...

    The idle mixture screws on Yamahas usually aren't cross-drilled, so if
    you can squirt B-12 through the idle jets and have it squirt back out
    the idle air inlet, the jet isn't that badly plugged. A very fine
    sewing needle will help to gently poke out the idle jets...
    krusty kritter, Apr 16, 2005
  6. Mike

    Mike Guest

    Thank you all for the replys.

    To answer some of the questions: I have used a carb cleaner as
    recommended a few months ago. I used yamaha's cleaner that you put
    directly into the carbs and let sit, and i also used a fuel additive
    cleaner. I have not tried barryman's b12, and i may look into that.
    The carbs were thoroughly disassembed and cleaned last spring, and only
    gave me minor trouble at the beginning of this year. I'll check out
    all the little pieces in the area I was working make sure i didn't
    disturb something i didn't mean to, and if i don't find anything, and
    barrymans doesn't do anything for me, then i'll just live with it since
    it doesn't sound entirely abnormal. Thanks again for your input.

    Mike, Apr 17, 2005
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