high idle when first start car

[ls954]

when i first start the car for the day that car just stay at high until i tap the gas peddle and once again when its warmed up a bit. A buddy of mine told me it was some type of spring, does anyone know the name of this spring and where its located?

[silicon212]

It's not a spring, it's the choke in action. This is normal behavior on a carbureted car. It has to be done this way, due to the way that fuel is atomized in a carb. With fuel injection, you get good atomization from the pressure of the fuel through the injector. On a carb, gasoline is not injected under pressure, but drawn from the carburetor float bowl from vacuum through the carb's venturi in normal operation. There is an idle circuit that delivers fuel when the throttle is closed to just off closed when there's not enough airflow to create the venturi effect. This idle mix gasoline tends more often than not to enter the intake in a stream, rather than a fine mix. When the engine is hot, the heat on and inside the intake will cause this fuel to vaporize, allowing a good burn in the cylinder. When the engine is cold, however, this gasoline will tend to pool in the intake and not properly mix, causing the engine to run sluggish due to the fact that some cylinders are rich and some are lean. Even though closing the choke helps out in this regard on a cold engine, more often than not a cold carbureted engine will stall at normal idle speeds, so something called the "curb idle speed" kicks in until the choke opens. The curb idle speed is determined by a cam on the carb that is operated directly by the choke. The idle speed screw rests against this cam, so that the throttle will be cracked open a little more when the choke is closed, causing the engine to run faster (and prevent stalling).

Hope this helps.

[ls954]

well being that is an electrice choke shouldnt it open up automatically causing the idle to drop? I know on my last caprice i had a manual choke which i had to push to open it and caused the idle to drop

[silicon212]

It will depending on how cold it is outside.

My car, FWIW, is pretty much identical to yours in the carb department. The electric choke will open up in a few seconds if it's in the 80s and higher, but if it's in the teens, etc, it could take considerably longer.

This time of year, it's about 2 minutes to heat on my car, and I live in metro Phoenix, AZ - cold temps are in the 30s and 40s this time of year. If it's colder than that, it will take longer still.

[ls954]

well its been pretty cold, like in the 20's and 30's, so ill give it a try tomorrow and check how long its stays in high idle. If the idle doesnt drop where would be a good place to start trouble shooting the problem?

[mike561]

same thing happens with mine, i took it for a drive today and i noticed after about 5 minutes of driving it the idle went way down and the engine got really quiet around where it should be.

[silicon212]

You should be able to adjust the electric choke by loosening the three screws holding the black cover plate on. IIRC, turning the cover to the right (clockwise) will enrich the choke (high idle run time increased), turning it left (counterclockwise) should lean the choke (high idle run time reduced). If, perchance, your choke cover plate is held in place with rivets instead of screws, don't worry. Although you can't loosen a rivet with a screwdriver (at least in the conventional sense), you can make the adjustment by carefully gripping the cover with channellock type pliers and then gently turning the cover in the desired direction.

[ls954]

ill have to try that adjusting method tomorrow.

This is what i did this morning. I started off by turning the ingition switch to "ON" and checked if i was getting any type of voltage to the choke, which i was, think it was like 2.8 or some where along those lines. I then proceeded to pump the gas couple of times and when i did that the two front barrels of the carb where closed, i then went ahead and started the car right up. The Two front barrels opened up slightly and i was getting 14. something volts at the choke, about 5 or 6 mins went by and the car was still at high idle and the two main barrels had opened up all the way and the car was up to normal temp. I stepped on the gas twice and the idle dropped to normal.

I did notice a clickin noise when i first turned the ignition to "ON" that lasted for couple of seconds, any idea what that is?

well like i said ill have to try your method tomorrow and see what happens.

[silicon212]

The 'clicking' sound is the sound produced by the carburetor mixture control solenoid (M/C solenoid) located within the bowl. It is produced as the computer 'pulses' it, should be a rapid clicking sound that will continue whenever the engine is running. If the key is turned to ON but the engine not started, it should click for about 5 seconds or so.

Your curb idle cam might be sticking a little if you have to press the pedal twice to get it to speed down. Try some carburetor cleaner.

[1968 Pontiac]

If you have some time on your hands you can drill out the rivets on the choke housing cover and install self tapping screws. Can't remember the size, but I think it's #6 or 8.

Also, if you decide to adjust your choke, make sure you mark where the cover was so you can go back if you have to.

Have a look at the ground at the back of your car where your exhaust exits. Is the ground black from a rich exhaust? If not, I wouldn't bother playing with the carb if everything else is running fine.

[GreyGoose006]

doesn't the high idle have a setting that makes it go down when you tap the gas pedal?
maybe i have a different carb, but mine idles high until i tap the gas, then it goes back down.

as far as i know, it stays high forever until i tap the gas, although i have never sat and waited for it more than a few minutes, or until it warms up enough to blow more than lukewarm heat in the winter...

[GreyGoose006]

also, what would the symptoms of a sticky or mal-adjusted choke be?
my car is running rich enough to foul the plugs with carbon after around 4K miles.
it also seems to stumble a lot and if i hold my nose right, i can make it backfire at will by tapping the gas when i'm driving.
also, whenever i start, i get black water out of the muffler. no oil in it, just lots of carbon.

its obviously running rich, but since i havent done any carb modifications except to rebuild, i dont know why.
the only thing i can think of is a choke sticking open
does this sound right?

sorry if this is a thread hijack, but at least its somewhat on topic...

[mike561]

yeah i have the black carbon spitting out of my tailpipe too. im going to try some carb & choke cleaner and make some adjustments on it too, hopefully that will ease things a bit.