[angie2020]

The real answer: First the assumptions. I assume that it is in fact adjustable because you give no date of the carb. If the carb pre-dates 1972 then it is. And I assume the intake manifold is a dual plane intake. And I assume that the car starts and runs but needs the A/F ratio tweaked. If it doesn't start, then set the screws at a base setting of two turns "out". A dual plane intake separates totally the intake runners between cylinder 1,3,5,7 and 2,4,6,8. Therefore 1/2 of the intake manifold serves fuel to the right bank and and the other half to the left bank. Therefore, the adjustment screws need not and should not be turned "in sync". If using a vacuum gauge as the writer above suggests, turn each screw independently for the highest vacuum. Then back-off screw 1/4 turn.

[hippich]

4 barell rochesters used 2 adjustment screws. With the engine off adjust the screws fully inward then turn them out 2 full revolutions. Start the engine and continue turing each screw by a quarter turn in sync with each other until the idle seems correct. If you are advanced enough you can also use a vacuum gauge attached to a manifold vacuum source and watch the vacuum readings while turing the screws. If the vacuum drops too much then you leaned it out too much and you need to go back a quarter turn or until suitable. Hope this helped.

[adamjkok]

If using a tachometer, the suggested way. Then turn one screw clock-wise for highest RPM (rich condition) and then turn the screw counter-clockwise (lean condition) until engine just stumbles; turn screw clockwise 1/4 turn. Do the same for the other adjustment screw. [links]

[yurumtin]

here

[Martian]

here

[Mahkul]

more

[crazylady552]

Locate the two idle adjustment screws in the front of the two-barrel Rochester carburetor and turn both screws clockwise with a screwdriver until they are completely closed. Be careful not to over-tighten the screws.

[arturekert02]

Turn the idle speed screw on the right side a quarter turn and alternate back and forth, adjusting the screws until you get the highest rpm readings possible on the vacuum gauge with the engine running smoothly. Continue the adjustments, alternating between them until both are reading the same rpm while running smoothly.

[melvster]

Remove the rubber vacuum hose from the base of the carburetor and attach a vacuum gauge to the vacuum port at the base. Start with the idle fuel mixture screw on the left side of the carburetor, looking at it from the front of the vehicle and turn the screw a quarter turn. [links]

[Foam]

Turn the adjustment screws back, counterclockwise one and a half turns with the screwdriver to use as a starting point for your adjustments. Start the engine and let it warm up for about five minutes. here

[DJFC]

Turn the engine off. Bench adjust the mixture screws by using the double "D" tool to screw the mixture screws, located on the front lower edge of the carburetor, into the carburetor until they lightly seat. Unscrew the screws two and one half turns. here

[BrBoy]

Start the engine and allow it to run until the thermostat opens and upper radiator hose becomes hot. Many Quadrajets are computer-controlled, and operating temperature must be reached before the idle mixture can be accurately adjusted. here

[nicklink483]

The idle screws on a Rochester Quadrajet carburetor fine tune the air-fuel ratio going into the engine during idle. The most common cause of rough idle quality in engines equipped with this carburetor is an unevenly adjusted idle mixture circuit caused by incorrectly adjusted mixture screws.

[SlipperySlope]

Start the engine. Screw the left idle screw into the carburetor until the engine starts to run rough. Slowly unscrew the screw and count the number of turns it takes to make the engine run rough again. Screw the idle screw back into the carburetor one half that number of turns. Repeat the process for the right side idle screw.

[Dark_Ghost]

Test drive the vehicle to verify that the engine doesn't stall or load up at stops. Adjustments to fine tune the idle quality should be done in quarter-turn increments, and should be done to both idle screws equally to maintain the balance of the idle circuit. [links]

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