Carburetor Adjustments

Hey...

I recently Rebuilt the 'Spare Carb' for my caprice. turns out its slightly different, so now I need to rebuild the original carb.

My question is, What should the mixture jets be set to? The spare Carburetor was set to 5 turns and 4.75 turns. the original carb was set to 8 turns and 4.5 turns.

The spare carburetor runs fine, but wont kick down to low idle. the original carburetor ran rich at low idle.

I live 781 Feet Above Sea Level if that makes any difference.

Also, when looking at the carburetor 'in operating position' there is an electric solenoid on the spare carburetor's front right corner that is not present on the original carb. Is this important, as the car runs without anything plugged into it?

Hey..
Also, when looking at the carburetor 'in operating position' there is an electric solenoid on the spare carburetor's front right corner that is not present on the original carb. Is this important, as the car runs without anything plugged into it?

The solenoid is an indication that it is an electronic computer controled Q-jet carb.
Not sure if the 86 came with them or not, my 89 has one.
If nothing is plugged into it, it is not performing as designed, you must not have smog checks up there.
I would keep it off if you can since it's not the best performance carb in the world unless modified..

I was checking these guys out for a rebuild on mine..

http://smicarburetor.com/products/sfID1/85/sfID2/86/sfID3/34

This is a Quadrajet, right? Your mixture screws are for the idle mixture only. As soon as you step on the gas, the carb stops using the idle mixture and transfers to the primary jets.

Both screws should be turned the same number of turns. If one is turned more than the other, you have an imbalance.

The best way to set the mixture is to use a vacuum gauge. If you don't have one, get one. They are cheap and handy to have.

Hook the gauge up to a manifold vacuum source. This vacuum is highest at idle and drops when you step on the gas.

Turn the mixture screws in all the way, but don't tighten them. Now, carefully open them 4 turns for each one. Start the engine and warm it up. With the choke opend and at low idle, look at the vacuum gause. It should read approx. 18 to 20 mmHg.

Now carefully turn both screws open one quarter turn each. Does the gauge show an increase or decrease in vacuum? Continue to turn both screws either in a bit or out a bit and watch the vacuum gauge. The correct mixture is achieved when the vacuum gauge is showing the maximum possible vacuum.

BTW, turning the screws out (opening them) richens the mixture. Turning them in (closing) leans the mixture.

FWIW, the 8 turns you had is probably too much (too rich).

Also, as noted above, don't use that electronic carb, since it will not run right unless the car is specifically designed to use one and has the appropriate ECM.

This is a Quadrajet, right? Your mixture screws are for the idle mixture only. As soon as you step on the gas, the carb stops using the idle mixture and transfers to the primary jets.

Both screws should be turned the same number of turns. If one is turned more than the other, you have an imbalance.

The best way to set the mixture is to use a vacuum gauge. If you don't have one, get one. They are cheap and handy to have.

Hook the gauge up to a manifold vacuum source. This vacuum is highest at idle and drops when you step on the gas.

Turn the mixture screws in all the way, but don't tighten them. Now, carefully open them 4 turns for each one. Start the engine and warm it up. With the choke opend and at low idle, look at the vacuum gause. It should read approx. 18 to 20 mmHg.

Now carefully turn both screws open one quarter turn each. Does the gauge show an increase or decrease in vacuum? Continue to turn both screws either in a bit or out a bit and watch the vacuum gauge. The correct mixture is achieved when the vacuum gauge is showing the maximum possible vacuum.

BTW, turning the screws out (opening them) richens the mixture. Turning them in (closing) leans the mixture.

FWIW, the 8 turns you had is probably too much (too rich).

Also, as noted above, don't use that electronic carb, since it will not run right unless the car is specifically designed to use one and has the appropriate ECM.

your mixture adjustment is good..the only thing I find off is after the max vacuum is reached you turn each mixture screw in [CW] 1/2 turn..the rpm should be around 750 when adjusting..

this was refered to as the lean drop ..

before any mixture adjustments are made the engine must be checked/repaired for any vacuum leaks...

the electric solenoid is used when the a/c compressor clutch is on..this is adjustible ..with the a/c on the idle should be slightly higher like 750 rpm in drive..with the a/c off the idle should be 600-700rpm in drive.
below this you risk stalling especially in winter..

to get the mixture adjusted better the use of the dwell meter is normally used ,,,but I have used both methods...I can get the same results ether way..

Found a repair manual online for the Quadrajet, haven't really looked through it yet, but I thought I'd post a link for all to see.

www.bdub.net/manuals/Quadrajet_Service_Manual_1981.pdf (http://www.bdub.net/manuals/Quadrajet_Service_Manual_1981.pdf)

Found a repair manual online for the Quadrajet, haven't really looked through it yet, but I thought I'd post a link for all to see.

www.bdub.net/manuals/Quadrajet_Service_Manual_1981.pdf (http://www.bdub.net/manuals/Quadrajet_Service_Manual_1981.pdf)

thanks looks good.