If your vehicle’s engine is powered by a fuel injection system, you must know the importance of maintaining fuel ratio or AFR. A balanced air-fuel ratio helps for preventing detonation and makes cooler combustion products inside your fuel injection, so you have to maintain the air-fuel ratio.

Adjusting the air-fuel ratio decides the speed of your engine running. So it is high time you need to learn how to adjust air fuel ratio fuel injection.

What is fuel injection?

What is fuel injection

Fuel injection is the process of injecting the fuel into the internal combustion engine of your vehicle. There are fuel injectors through which you can introduce fuel. These fuel injectors last about 1 billion cycles of your vehicle. Injecting fuel gives new life to your engine every time.

Efficiency is increased, a cleaner environment is ensured, and burning remains healthier after the fuel injection. Fuel injection technology removes the need for a carburetor. It enables the engine of your car to supply the fuel to the cylinder straight. Some sensors locate the level and ratio of the fuel that was injected. These are electronic sensors.

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What is the air fuel ratio?

What is the air fuel ratio

The Air fuel ratio or ideal air fuel ratio is a proportion of air to fuel. It ensures that there is no oxygen and fuel left after combustion. The exact air fuel ratio is approximately 14.71:1. That means you need to keep 14.71 portions of air for 1 portion of the fuel. But it varies from car to car.

Like, the sprint car has two air fuel ratios according to its cooling system. They are 6:1 or 3.4:1. It also depends on the experience of the tuner. When combustion happens, the air fuel ratio is made. Gas and air go into the cylinder, and CO2 and water are made. This works as the air pressure.

Why adjusting the air fuel ratio is important?

Why adjusting the air fuel ratio is important

If you have a gasoline engine, the air fuel ratio is a good indicator to measure its performance. Controlling and tuning the engine also depends on the air fuel ratio.

How to adjust air fuel ratio in fuel injection?

adjust air fuel ratio in fuel injection

There are many ways to perform the task, but here I’ll show you two ways. You have to select one method according to the tools available to you, your engine carburetor, and the tuning of the carburetor.

Method no 1 : Tightening the screw

Tightening the screw

There is a little screw named the air-fuel ratio screw. It is situated at the right on the metering block in the holly carburetor. If yours is an Edelbrock carburetor, you will find the screws (usually two) in the front of the four-barrel.

These screws control how much air is mixed with the fuel. Adjusting the screw works as adjusting the air fuel ratio in fuel injection. It also works on how fast and how slow your engine idles. The engine’s running smoothness is also measured by the tightening of the screw. This process is also called listening to the RPM (revolution per minute) of your injector.

Step 1

Warm up the engine by starting it. Keep it like that for 5 minutes. Let it idle.

Step 2

Take the screwdriver and turn the screw clockwise. Keep turning until you hear the engine sound. It may be a little rough cause the engine is slowing down.

Step 3

Pull out the screw-like a half-turn, and you can see the engine’s speed is backing up.

Do the screw thing on both sides of the carburetor. If your carburetor has four screws, then cover up the fours.

Method 2 : Vacuum Gauge

Vacuum Gauge

For the non-tuned carburetor, you can use an innovative vacuum meter to measure the air fuel ratio and adjust it to the ideal mark.

Step 1

Hook up one side of the vacuum meter with the cigarette lighter, and the other O2 sensor will be connected to the exhaust. You can use an adapter while putting the O2 sensor into the exhaust.

Step 2

Power the vacuum meter up and check the O2 sensor.

Step 3

Now the adjusting part is near. If you can see the ratio at 14.7:1 through the vacuum meter, you are set, but if you witness any changes in the number, go and set some of the springs, jacks, and needles.

Put the needle inside the carburetor and recheck the air fuel ratio. This will work immediately. You may have to change the main gaze sometimes. After getting all the glitches done, the innovative vacuum meter will show the perfect result of your air fuel ratio.

No matter how well you think, your air fuel ratio is, there can be some problems in estimation. So measuring the air fuel ratio with the vacuum gauge is a good option.

Things you need to remember:

  1. Always adjust the air fuel ratio in the fuel injection of your car while the engine is warm.
  2. Do not lose or tighten any of the screws without being sure of it. Your ignorance and overconfidence can ruin your engine.
  3. If the adjusting screw is tightened, the air fuel ratio becomes leaner and lowers the RPM. This ensures the engine is idled.
  4. You can adjust the flow rate of the fuel injector by changing its size of it. You may change it until you catch the ideal air fuel ratio.

Frequently Asked Questions

1. Can I adjust the fuel injector?

Answer: No, you can’t adjust the fuel injector. If you try to get higher pressure than the limit of your injector, then it can harm your engine.

2. Explain the ideal air fuel ratio?

Answer: The exact air-fuel ratio is fixed. It is 14.7:1. That means the “stoichiometric” mixture of air and fuel. If you have 14.7 parts of air, 1 part will be the fuel.

Final Words

Balancing the air fuel ratio is necessary for your engine’s health. Your engine will run too lean if the air fuel ratio is imbalanced. Now, as you know how to adjust air fuel ratio fuel injection, it’s time to grab the tools and get to work.


Hi, my name is Gabrielle. I have been into Automotive Industry for over 15 years. If you’re anything like me, then building, maintaining and improving your Automotive Industry/Projects is all part of the Automotive experience. My goal with this blog is to share my experience with and help you discover new and exciting things about Automotive.