1988 Accord VERY high RPM

Discussion in 'Accord' started by J & G Park, May 16, 2004.

  1. J & G Park

    J & G Park Guest

    My daughters 88 Accord LX starts fine and then stays at about 2000 RPM. I
    have checked for bad vacuum hoses etc. and I can't find anything broken. Can
    anyone suggest what is wrong, she needs this car for work and we can't
    afford to get another car at this time.

    THANKS IN ADVANCE !
     
    J & G Park, May 16, 2004
    #1
  2. J & G Park

    Eric Guest

    It sounds like the choke may be sticking on. There could be several things
    to cause this. First, you should verify that this is indeed the case.
    Remove the top of the air cleaner and the round brass colored screen over
    the carburetor throat. You should be able to see the choke butterfly valve
    at the top of the primary barrel. As the car warms up, this valve should
    open up. If it doesn't, then you'll need to do a little diagnosis. The
    linkage may be sticking and may simply need to be cleaned. Or, the choke
    heater coil may not be receiving current. You'll need to check that you
    have voltage on the two wires for the choke coil. Another possible cause is
    that there is a paper gasket underneath the choke heater coil which, for
    unknown reasons, deforms and in extreme cases may interfere with the
    operation of the choke. The choke heater coil, which is actually an
    electrically heated bimetal spring which opens the choke, is riveted on to
    the carb so the rivets must be drilled out in order to replace the gasket if
    you think that it's interfering with the operation of the choke.

    Eric
     
    Eric, May 17, 2004
    #2
  3. J & G Park

    Aron Guest

    If the choke stuck closed, wouldn't the RPM be low? The choke heater has
    one wire. It is white and runs from the choke cover toward the back of the
    carburetor where. There is a connector back there. You can check that it's
    getting voltage, but I think your problem would be different if it were the
    cause. I would inspect the choke opener and the fast idle unloader. If
    either is leaking, the fast idle unloader may not unload completely. Write
    back if you want a description of the tests but you need a vacuum pump and
    gauge.

    A quick visual inspection would be to open the air cleaner case and look
    in the main bore of the carburetor. This is the one that has a flap near
    the top. This flap is the choke. You may need to take the screen off the
    top of the carburetor to see it well. Just be careful not to drop the nuts
    where they don't belong. The flap should close the bore after you push the
    gas pedal to the floor and release it. It should stay closed while the key
    is in the start position and the engine is cranking but it should
    immediately open partially when the key is released. It will slowly open
    until it is opened completely or until the car warms up enough that the
    choke opener pulls it open completely. The choke should be fully open (flap
    vertical) at normal operating temperature.

    Here is how the automatic choke/fast idle system works. You need a very
    rich mixture to start the car and a leaner mixture in order to run as soon
    as it starts. You also need a mixture that becomes more lean as the car
    warms up until it is fully warmed up. Once it is warmed up no choke is
    needed and the mixture is completely regulated by other parts of the
    carburetor. When you start the car, you push the pedal to the floor and
    release it. This allows the choke spring to close the choke. With the
    pedal released the choke and throttle are now closed, cutting off as much
    air as possible. With the air mostly cut off, the vacuum from the engine
    while you are cranking it goes mostly to drawing in fuel, resulting in a
    very rich (lots of fuel and little air) mixture.

    During cranking, something called the crank leak solenoid valve, bleeds
    vacuum to the outside air, away from the choke opener stage 1 diaphragm.
    When the engine fires and you release the key, the solenoid closes off the
    vacuum leak and the vacuum is applied to the stage 1 diaphragm of the choke
    opener. The motion of this diaphragm moves a rod connected to the choke and
    opens the choke a fixed amount. This is how you get the very rich mixture
    you need to start the engine followed by a much leaner mixture needed to run
    it once it fires. At this point the choke is still partially closed and the
    choke heater is heating a bimetallic spring. This spring will slowly open
    the choke. Once the coolant temperature reaches 50C, I believe, Thermovalve
    A moves to it's stage 2. This applies vacuum to the second diaphragm of the
    choke opener, causing it to open to it's stage 2, which fully opens the
    choke. At this time vacuum is simultaneously applied to the first diaphragm
    of the fast idle unloader and the idle comes down somewhat. When the
    coolant temperature reaches the Thermovalve A stage 3 temperature, vacuum is
    applied to the second diaphragm of the fast idle unloader and the idle
    drops.

    Aron
     
    Aron, May 17, 2004
    #3
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