How to Adjust a Carburetor on a Dirt Bike?

Written by

James Stevens

Fact-checked by

Robert A. Verdin


Carburetors are an important part of a mini bike or full-sized dirt bike, as it’s responsible for proper air-fuel mixing and optimal power delivery to allow the engine to run smoothly.

Although carburetors mostly only require cleaning, such as where they are dirty, have poor throttle response, or poor idling, there are also situations where a dirt bike carb tuning is necessary.

The idea may seem challenging, but it’s actually doable on your own. To know how to adjust a carburetor on a dirt bike, continue reading below!

Ways to Adjust a Dirt Bike Carburetor


Whether you have a 2 stroke or 4 stroke dirt bike, your carburetor functions almost the same, and they require almost the same process of adjustment.

Here’s a diagram of the carburetor to help familiarize yourself.

Its are the following. Take note of these parts because they’re important for the dirt bike carburetor adjustment.

  • Pilot jet
  • Main jet
  • Air screw (between the float bowl and air intake)
  • Fuel screw (near the float bowl, downstream of the fuel entry)
  • Idle screw

Step 1: Prepare

To tune a dirt bike carburetor, here’s what you need to prepare in general:


  • Screwdriver
  • Pliers
  • Allen wrench

Step 2: Test your dirt bike.

The first step in doing carburetor adjustment is to test your dirt bike to find out what’s wrong with it. For instance, you need to check how your engine runs when it’s idling.

The idle speed pertains to how fast or slow your dirt bike moves when you release the brake while the engine is running. Thus, if your dirt bike has poor idling, it may be a sign to adjust your idle screw.

Step 3: Adjust idle screw


Your dirt bike’s idle screw is typically located on the side of the carburetor.

  • To adjust the idle, use a Phillips-head or flat-head screwdriver; turn your idle screw clockwise if you want your idle speed up but counterclockwise if you want to make it lower.
  • Make sure you adjust your idle screw once the dirt bike is already warmed up and the choke is off.

But how will you know the ideal idle speed of your dirt bike? It actually depends on the type of motorcycle.

For instance, the ideal idle speed for a 2-stroke dirt bike is around 1200 to 1500 RPM. However, for a 4 stroke dirt bike, the idle speed could be 1800 to 2000 RPM or lower.

Your best bet is to look in the motorcycle user manual and keep an eye on the tachometer while doing this step.

Make sure you test your dirt bike after each adjustment as well. If it’s running smoothly or according to your liking, you’ve perfectly adjusted your carburetor!

Step 4: Adjust the main jet


The main jet is responsible for regulating the amount of fuel that’s delivered to the engine.

  • Loosen the intake clamps and carburetor bowl or plug to access the main jet.
  • Turn your main jet screw clockwise or counterclockwise with a screwdriver, depending on whether you want to increase or reduce the amount of fuel that’s going to your engine.

However, if your engine still lacks power after adjusting your main jet, it may be time to replace it with a larger one. On the other hand, if your engine still needs a leaner fuel mixture, it may be time to have a smaller main jet.

Step 5: Adjust the air screw and pilot screw


The air screw and pilot screw of the dirt bike control the amount of air that is mixed with your fuel.

Remember, a rich fuel mixture will make your dirt bike harder to start and perform badly in higher elevations. Meanwhile, a lean fuel mixture can lead to overheating and too much idling.

  • The air screw is usually a small knob located near the air filter.
  • Once your engine is off, unscrew the air screw until it somehow bottoms out. Turn it clockwise if you want to make your air-fuel mixture richer and counterclockwise if you want to make the mixture leaner.
  • Turn the pilot screw in or out so that it has the number of turns required by the manufacturer.

During the process, use half-turn increments until you have the proper setting.

Note: Never over-tighten the air screw to avoid damaging it or making it difficult to tune.

Step 6: Test your dirt bike again.


Once the adjustment screws are all tuned up, test your dirt bike again to ensure your carburetor is working properly. If there are still issues, just repeat the process and make more adjustments.

If you feel that your dirt bike is running smoothly without the issue of poor idling and weak engine performance, congratulations! You’ve succeeded in fine-tuning your air/fuel mixture screw, main jet, and idle screw.


In summary, learning how to adjust a carburetor on a dirt bike on your own isn’t impossible at all! You only need to check what adjustment your carb needs, such as if you need a leaner or richer fuel mixture and higher or lower RPM.

Be patient if you’re not able to fine-tune your carburetor by doing a single adjustment, and just continue to follow the steps above.

Remember, with patience and practice, you can tune a dirt bike carburetor successfully. Now, you no longer have to worry about running into engine issues. Have fun tuning!

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James Stevens

James Stevens is an expert bike mechanic who knows everything from basic repairs to custom modifications. What sets him apart is his ability to explain complex concepts in a way that's easy to understand. Check out his content on Speedway if you need help with upgrades or modifications for your bike.