How to Adjust a Carburetor

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At some point, you might experience a rough-running car engine or even a rough-running lawn mower. Many times, all that is needed is an adjustment to the carburetor, which can be done by adjusting the air and fuel mixture, adjusting the idle, or doing both. The correct air and fuel mixture helps with vehicle mileage (or fuel efficiency in a lawn mower) and the correct idling speed keeps the engine from running too fast or too slowly. Adjusting the carburetor in your car can be done with just a few simple steps and no special tools.

Steps

Adjusting the Air and Fuel Mixture

1. 1
   Turn the engine off if it is running.

   
   
2. 2
   Open the hood of the car.
3. 3
   Locate the air filter.
4. 4
   Remove the wing nut from the air filter.
5. 5
   Remove the air filter; the carburetor will be visible as the part to which the filter was screwed.
6. 6
   Find the 2 screws on the front of the carburetor; these are used to adjust the air and fuel mixture.
7. 7
   Restart the engine and let it warm to normal operating temperature; you will know this by the sound of the engine or you can check the temperature gauge.
8. 8
   Adjust 1 screw slowly clockwise, counting the number of turns, until the engine begins to run rough, sputter or die.
9. 9
   Adjust the second screw in the same way and for the same number of turns. Both screws must be adjusted equally to achieve the correct mixture.
10. 10
    Turn both screws, 1 at a time, back out 1/4 to 1/2 turn at a time until the engine begins to run smoothly.
11. 11
    Turn both screws counter-clockwise, 1 at a time, an additional 1/2 turn or until the engine begins to run rough again.
12. 12
    Turn both screws clockwise again, 1 at a time, to the point at which the engine ran best.
13. 13
    Replace the air filter assembly.

Adjusting the Idle

1. 1
   Turn the engine on and let it idle or drive the car until it is warmed up (as above).
2. 2
   Turn the engine off.
3. 3
   Repeat the steps above to remove the air filter.
4. 4
   Find the throttle cable and the idle adjustment screw attached to it.
5. 5
   Restart the engine.
6. 6
   Turn the idle adjustment screw 1/2 turn to the right to tighten.
7. 7
   Listen to the car's engine for sounds of roughness.
8. 8
   Wait for 30 seconds for the engine to adjust to the change.
9. 9
   Continue to turn the idle adjustment screw 1/2 turn at a time until the engine runs smoothly.
10. 10
    Replace the air filter assembly.

Video

Tips

• Tightening the idle adjustment screw increases idling speed while loosening the screw decreases idling speed.
• If your car is equipped with a tachometer, you can use this as a tool to adjust idling speed (revolutions per minute or RPMs). Check your owner's manual for the correct RPMs.
• If after adjusting the idle mechanism, the engine does not run smoothly, go back to making air and fuel adjustments and repeat the steps for both air and fuel and idling adjustments.

Warnings

• Remember that when you are working on a carburetor, you are working with a fuel source. Take all necessary precautions for working around gasoline.

Things You'll Need

• Flat-head screwdriver
• Pliers or vise grips
• Paper towels

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