How to Adjust the Carburetor

Most modern cars will employ the use of computer-controlled fuel distribution systems. However, older model vehicles are still prevalent and do not have this feature. Instead, they will have a more traditional method of fuel distribution that uses a carburetor. Rather than being automatically controlled by the vehicles computer, a carburetor is a mechanical component that sometimes needed manual adjustment. Thus, knowing how to adjust the carburetor was a necessary skill.

If you notice black colored smoke, lower engine performance, backfiring, overheating, or hard starts, you may want to take a look at your carburetor to see if adjusting it may be the problem. If your car uses a carburetor for fuel delivery, it is a good idea to know how to adjust the carburetor. Luckily, this is a simple task that does not require too much time and very few tools. This article will give you a step by step method to help you easily learn how to adjust the carburetor on your vehicle.

Things You Will Need

• Set of screwdrivers
• Safety gloves
• Safety glasses
• Carburetor adjustment tool (optional)

How to Adjust Carburetor Method

1. The first thing you will need to do is make sure you park your vehicle on a level area. It is a good idea to place the parking brake in the on position for added safety while you work on your vehicle.

2. Safety is key when working on any part of your car. This includes learning how to adjust the carburetor. Use eye protection and hand protection as parts may be hot, have pinching possibilities, or debris may be thrown towards your vulnerable eyes.

3. Open the hood and ensure you lifted it securely by means of the hood prop rod.

4. Find your air box. The housing is usually a black, round box-like part that is either plastic or metal and exists near the engine and secured to a duct that runs toward the front of the car.

5. Next, you will need to remove the air filter located within that box. To do so, you will likely need to loosen a hose clamp that seals the duct and remove a few screws that hold the cover on. Some types of filter boxes will have wing nuts or quick release snaps. You should now be able to remove the filter and then the housing in order to access the carburetor.

6. Next, when learning how to adjust the carburetor, you will need to adjust your air/ fuel mixture. A proper air/ fuel mixture is important because your engine uses the combustion it creates to burn the fuel appropriately, giving you good fuel economy and stopping issues like overheating.

Once you remove the filter and its housing, you will be able to access the exposed carburetor. Locate the air/fuel adjustment screws. They are usually plain flathead screws. Depending on the type, make, and model your carburetor may have up to four adjustment screws.

7. To begin you will want to watch your engine condition by starting your car and allowing it to heat to operating temperature. Determine if your engine is running too rich (using too much fuel), or running lean (not having enough fuel).

8. To adjust your air/ fuel ratio, use either a flathead screwdriver or your carburetor adjusting tool to turn the screws on your carb. Tightening the screw will increase the used fuel amount. Be sure to only increase the fuel in small amounts, preferably in quarter turns until you reach the correct amount. Now is the time to notice if there are any issues with the fuel injector as well.

• To begin, turn the adjustment screws back until your vehicle is running slightly lean. You will know you are lean when you hear the vehicle sputter, run roughly, and eventually stall.
• Just before a stalling setting, begin to slowly tighten the screws in quarter turn increments until you hear your engine begin to run smoothly. Be sure to tighten all screws equally when making adjustments.
• A vehicle that is “running smoothly” will exhibit a steady idle free from backfiring or any vibration. It should remain shake and “popping” free even when you rev your engine through each rpm range.

9. Test your engine by observing it during idle and as you rev the engine through RPMs, both high and low. If you experience any shaking, sluggishness, backfiring or signs that you are going to stall, continue to give the ratio additional fuel by twisting the adjustment screw a bit more.

10. Once you properly set the air/ fuel mixture, the next step in learning how to adjust the carburetor is to locate the idle mixture screws. These are responsible for controlling the air/ fuel mixture during idle speed. Typically they are near the vehicle’s throttle plate. However, these screws can vary greatly between vehicles. Thus, be sure to consult your owner’s manual in order to identify the correct screws.

11. Continue to adjust these screws in a similar way you did the last set. Ensure you have a smooth idle and that your engine continues to run smoothly when you rev the engine.

12. Once you are happy with the idle speed and revving does not show sudden drops in rpm or causes stalling, you can proceed to the reinstallation of your filter and filter housing.

13. The final step in how to adjust the carburetor is to take your vehicle for a test drive. Take note of how responsive it is, that you are getting good power, fuel efficiency and that it continues to run smoothly. If you notice any negative aspects, you can go back and make more adjustments to the carb.

Finally, if you need some more information, you can watch this clip about carburetor adjustment basics:


A well-adjusted carburetor is critical to the engine performance of your vehicle. If you are experiencing poor fuel economy, backfiring, overheating, or stalling, you may have a poorly adjusted carburetor. Luckily, with a little practice, you can quickly take care of the issue yourself. So, save yourself time and money with these step by step instructions to help you learn how to adjust the carburetor.

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