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Old 16 May 2004, 03:47 pm
J & G Park
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Default 1988 Accord VERY high RPM

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 !


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Old 17 May 2004, 03:33 am
Eric
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Default Re: 1988 Accord VERY high RPM

J & G Park wrote:
>
> 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.


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
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Old 17 May 2004, 09:44 am
Aron
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Default Re: 1988 Accord VERY high RPM

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




"Eric" <say.no@spam.now> wrote in message news:40A878D2.6BAF481F@spam.now...
> J & G Park wrote:
> >
> > 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.

>
> 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



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