1986 Virago 1100 Starting Problems

Discussion in 'Motorbike Technical Discussion' started by juggalo080, Jul 13, 2005.

  1. juggalo080

    juggalo080 Guest

    Hey, I’m new here and would like to thank anyone who helps me out with
    my problem. I got the bike from someone when it was not running.

    The enging has 150lbs of compression in both cylinders.
    I just put carb kits into the carbs. The kits had the jets,
    needle/seat and such things that I replaced. I also sprayed carb
    cleaner pretty good into there when I had the parts out.

    The pilot screw I had turned out about 3 1/2 turns after the rebuild.

    The plugs are new. I checked both plugs for spark and they look good.

    When cold I have to pull the plugs and put fuel into the cylinders to
    get the bike started. When it is started it only runs on one
    cylinder(the front one).

    In effort to get the rear cylinder to run i played around with the
    idle mixture screw and got nowhere.

    I ended up unhooked the hose that goes to the front of the carb and
    sticking my hand over it for a few seconds, then letting off. It
    would run on both cylinders for a short time after I do that until it
    runs out of the fuel I just made push into there.

    I did not clean out the tank or fuel petcock before I rebuilt the
    carbs. The fuel petcock was leaking around a piece that goes up in so
    I put a little silicone on to keep it from leaking until I get the
    bike running right and spend the money on a new or used petcock.

    I opened the drain plug on both of the carbs to check and make sure
    that there is fuel in there and there was. I do not know if the
    floats are set to the right height or if they could cause this
    problem? I’m not sure how much fuel is actually in the fuel bowl but
    I do know there was some.

    The fuel petcock has a vacuum line into it which aparently somehow
    gets the gas to flow when being started. What does "PRI" mean on
    the petcock though?

    Sorry for the long post but I figured I should give all of the
    information that I know so that the problem could be easier to

    Thanks for any info.
    juggalo080, Jul 13, 2005
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  2. You've probably opened it too far (1), but the engine does NOT rely on
    the idle circuits to start...

    Each of your carbs has a starting enrichener device instead of a choke.
    It's in a bypass passage that goes around the main carburetor bore.
    When you turn the "choke" knob ON, you're just opening a tiny valve in
    the side of the carb. The engine won't get enough fuel to start if the
    throttle butterflies are too far open. Turn the master idle knob all
    the way down and don't turn the throttle at all when you try to start
    the engine. If the engine still won't start, the starter jet in the
    float bowl might be plugged up...

    If the engine runs on the starting enrichener, but quits when the
    knob is turned OFF, the fuel/air mixture bypass passages are probably
    plugged up. Fuel is sucked up through the idle jet into the bypass
    passages that go around the throttle butterflies. There are three
    transition ports arranged in a triangle and the the throttle
    butterflies just cover them up when they are closed. If you squirt carb
    cleaner through the idle jet, it should come out through those three
    transition ports and also should come out the single pilot fuel/air
    mixture port about an inch downstream of the transition ports...
    When you hand choke the engine like that, you're sucking fuel through
    the needle jet, the idle jets, and the starter jet because you've made
    a lot of vacuum in the carbs. But if the engine doesn't keep running
    it's because there's not enough vacuum downstream of the throttle
    butterflies or because the starter jet or the idle bypass passages are
    plugged up...
    If you have a short piece of clear plastic aquarium tubing, attach it
    to the float bowl drain spigot and open the drain screws. If you hold
    the tubing in a bent "U" shape alongside the carb, you should see that
    the fuel level is about even with the float bowl gasket surface...
    PRI means "prime". The prime setting opens a port that bypasses the
    automatic vacuum operated valve on the back side of the petcock...

    (1)The idle mixture screw only adjusts ONE of four idle mixture ports.
    The other three ports bypass the throttle butterflies. When you open
    the idle mixture screw too far, you have to open the throttle
    butterflies slightly to compensate, and this uncovers the
    non-adjustable transition ports downstream of the butterflies. Then the
    engine runs far too rich and confuses the heck out of newbie tuners.
    The engine RPM "hangs up" when they blip the throttle and it takes a
    long time to idle down again.

    You will eventually have to readjust the idle mixture screw, starting
    from about one full turn open, and turning the screw in the CLOSED
    direction and turning the master idle knob DOWN until you get the
    fastest smooth idle speed for the least amount of throttle opening.

    You'll know you have the idle screws adjusted right when the engine RPM
    doesn't "hang up", the engine starts on just the "choke" without giving
    it any throttle, the engine warms up quickly, and doesn't stall when
    you roll the throttle off...

    There is nothing you can do about the exhaust backfires as you roll the
    throttle off, that's a characteristic on an engine that fires a "waste"
    spark while the exhaust valve is open. It lights off any unburned
    mixture in the pipes...

    But you can begin to understand what the piffle-piffle-SNAP! or the
    fart-POP! sound in the exhaust pipe means. That's a symptom of plugged
    up idle passages or idle jets...
    krusty kritter, Jul 13, 2005
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