A carburetor has an important function on your go-kart; it ensures that your engine receives the optimal air-fuel mixture. Running on a lean fuel mixture can lead to misfires and loss of low-end torque, whereas running on a rich fuel mixture can lead to engine knocking and poor fuel economy.
Therefore it’s extremely important to ensure that the carburetor on your go-kart is set correctly. There are two screws that you can adjust, in order to ensure that your engine receives the right fuel mixture and that it has the right idle speed.
Here are the two carburetor adjustments for your go-kart:
As you can see in the illustration below, there are two different set screws that you can adjust. The first screw is the pilot screw, which lets you adjust the air-fuel mixture. The second screw is the idle screw and let’s you set the idle speed.
In this guide, we’ll be taking a closer look at how to adjust your go-kart carburetor. You should only make adjustments if you notice your go-kart not performing optimally, if you’re setting up your carb for the first time or if your carburetor was previously incorrectly calibrated.
1. Air-Fuel Adjustment (Pilot Screw)
The first adjustment that I will guide you through is the air-fuel adjustment, which ensures that your go-kart engine receives the optimal air-fuel mixture. In order to achieve this, you’ll need to locate the pilot screw.
Where to Find the Pilot Screw
The pilot screw is usually located on the air intake side of the carburetor, which is attached to the intake manifold and the air filter. You may use the image above as a reference.
In some carburetors, the pilot screw is located on the fuel inlet instead. If the adjustment screw is located near the fuel inlet, it’s referred to as a fuel screw and if it’s located near the air intake, it’s called an air screw. Generally, these screws are referred to as pilot screws.
How to Adjust the Air-Fuel Ratio
The function of the pilot screw is to restrict or increase air/fuel flow into the carburetor depending on where it’s located (air intake or fuel inlet). By adjusting the inflow of air or fuel, you’ll be able to ensure that your engine receives the optimal air-fuel ratio.
- Lightly fasten the pilot screw – Firstly, turn the pilot screw in clockwise until it’s seated. You can do this with any compatible screwdriver. Remember not to tighten the screw and stop the moment you feel some form of light resistance.
- Return to factory setting – The first step was done to give you a reference point. Now, turn the screw counterclockwise (loosen it) by 2 full turns. This is the factory setting and should typically be optimal for your go-kart.
- Finalize air-fuel adjustment – In this step you should turn your engine on and let it run. You should listen closely and observe if your engine is receiving the right mixture of air and fuel. You will also need to take your go-kart for a ride, as you’ll also need to test it at different RPMs.
It’s important to listen to the go-kart engine sound carefully and test your carburetor adjustments. If you observe that the engine is bogging, the fuel mixture is too lean and you’ll need to adjust the pilot screw to restrict the amount of air that goes into the carburetor. You can do this by tightening the pilot screw slightly.
If the mixture is too fuel rich, you’ll notice that the engine is sputtering. In that case, loosen the pilot screw to let in more air into the mixture. Remember to always make small adjustments and test your new air-fuel settings through various RPM ranges.
Tightening the air-fuel screw restricts the air intake and makes the fuel richer.
General rule for adjusting the air-fuel mixture
Loosening the air-fuel screw increases the air intake and makes the fuel leaner.
Idle Adjustment (Idle Screw)
The second adjustment that you can set is the engine idle speed, which is done through the idle screw on your carburetor. An engine running at a low idle speed can lead to vibrations and can cause the engine to shut off. If the idle speed is too high, you’ll be burning more fuel. Therefore, having the engine run at the optimal idle speed is important.
Where to Find the Idle Screw
As you can see from the reference image above, the idle screw is typically found on the neck (center) of the carburetor and increases or reduces air-fuel flow into the go-kart engine.
As not all carburetors look the same. Therefore, some idle screws look similar to the air-fuel screw that require a screwdriver, while others are finger screws that allow for easier adjustments.
How to Adjust the Idle Speed
The function of the idle screw is to enable you to set the idle speed of your go-kart engine. The idle screw controls the amount of air and fuel enters the engine and the more you let the carburetor pump in, the higher the idle speed of the engine. Conversely, the less air and fuel enters the engine, the lower the idle speed.
Depending on the screw type, use a suitable screwdriver or your fingers to set the idle speed. You’ll need to do this with the engine switched on and in neutral gear.
Let the engine idle and observe the sounds and behaviour of the engine idling. If the engine idle speed is too low, turn the idle screw clockwise to allow more fuel and air to enter the engine.
On other hand, if the idle speed is too high, turn the idle screw counterclockwise to restrict fuel and air flow to the engine. The trick here is to try several adjustments and develop a feel for it. Practice makes perfect!
Tightening the idle screw restricts fuel and air and reduces idle speed.
General rule for adjusting the idle speed
Loosening the idle screw increases fuel and air and increases idle speed.
