How to Adjust the Idle on a Monte Carlo

by Carl Pruit

The Chevrolet Monte Carlo has typically come stocked with a 2 or 4 barrel carburetor, depending on the size of the engine. These carburetors have two adjustment screws to give you the best fuel efficiency for your Monte Carlo. The idle mixture screw allows the fuel to enter the carburetor at the specified amount based on how you set the mixture, while the idle speed screw adjusts the amount of rpm's that the engine will reach at idle speed. When you adjust the idle on your Monte Carlo, these two adjustments screws can give you the best possible performance for your vehicle.

Step 1

Put your vehicle transmission in park, and set the emergency brake to keep the car from rolling. Lift the hood, and remove the air cleaner from the top of the carburetor by unscrewing the wing nut on the top of the air cleaner by hand.

Step 2

Start your car, and allow it to idle until it warms up, and the carburetor choke opens up. Connect the tachometer to the engine by placing one of the lead wires on the negative ignition coil post, and the other lead wire to the vehicle frame. Remove the vacuum hose leading to the carburetor vacuum outlet valve, and attach the vacuum gauge to the outlet valve.

Step 3

Turn the idle mixture screw, the higher of the two screws, with a screwdriver clockwise until the valve is closed completely, and then turn it back (counter-clockwise) 2 full turns. Repeat this process with the idle speed screw (near the bottom of the carburetor).

Step 4

Turn the idle speed screw until the vacuum gauge reads 850 rpm's, and then turn the mixture screw clockwise about 1/4 of a turn to lean out the fuel. The idea is to reach the leanest fuel mixture possible, while allowing enough rpm's to keep the vehicle running at idle.

Step 5

Look at the vacuum gauge, and see if the rpm's have changed. Turn the idle speed screw again to return the rpm's to 850 rpm's. Turn the mixture screw another 1/4 turn clockwise to continue leaning out the fuel. Continue this process until the engine is about to starve out for fuel at idle, and turn the mixture screw the opposite direction (counter-clockwise) about 1/4 turn.

Step 6

Adjust the idle speed screw one more time, until the vacuum gauge reaches 850 rpm's. Remove the vacuum gauge from the carburetor, and put the vacuum hose back on the carburetor vacuum outlet. Detach the tachometer from the ignition coil, and put the air cleaner back on top of the carburetor. Secure the air cleaner to the carburetor with a wing nut, and turn the engine off.

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